BIOE 107 Final Study Guide

What is meant by a "species-area" relationship (or species-area curve; if logged then it becomes a straight line)? Provide an example of an equation for a species area curve, pointing out what each variable means. Then, using a graph, show how species-area relationships for islands versus mainland areas demonstrate that both the size of the area assessed and its insularity (island-ness or degree of isolation) affect the number of species found in an area.

* refer to final diagram 120 The "species-area" relationship is that big islands have more species than small islands, aka the size effect. S = cA^z where S = # of species, A = area, and c + z = constants fitted to data. Based on graph, mainland is larger (takes up more space on the x-axis) and has more species than the island.

***Below is a typical Lotka-Volterra interspecific competition model shown graphically as the isoclines of two species plotted as a function of the density of species 1 (N_1) and the density of species 2 (N_2). Show with the use of arrows and vectors the joint movement of both populations for each region of the graph (each region is defined with reference to the isolines). Then describe, with reference to the isoclines, why the joint movement in each region is the way it is (why the arrows point the way they do). State what the outcome of competition is in this system (name the outcome and also show on the graph where the population will eventually stabilize). Illustrate, by drawing lines from the equilibrium point to each axis, the equilibrium population sizes of N_1 and N_2.

* refer to final diagram 83 Anywhere on each individual line is where the population is stable. If you are above the line, you are above the carrying capacity and the population is declining. If you are below the line, you are under the carrying capacity and the population is increasing. When drawing the arrows and vectors, you first look at each species' isocline separately. Species 1 will have horizontal arrows. Below the isocline, these arrows will be pointing to the right to indicate the population is growing, and above the isocline, they will be pointing left to indicate the population is declining. Species 2 will have vertical arrows. Below the isocline, these arrows will be pointing up to indicate the population is increasing, and above the isocline, they will be pointing down to indicate the population is decreasing. The vectors are drawn pointing diagonally from the combination of the other two arrows. So, under both lines, the vector points diagonally to the right and up as both species are experiencing growth. Above species 1 and under species 2, the vectors points diagonally to the left and up, as species 1 is declining and species 2 is increasing. Above both lines, the vector points diagonally left and down, as both species are declining. Above species 2, but below species 1, the vector points diagonally to the right and down, as species 2 is decreasing and species 1 is increasing. In this case, the outcome is stable coexistence and it will reach equilibrium where the lines intersect.

***Repeat the above exercise with the following graph. Below is a typical Lotka-Volterra interspecific competition model shown graphically as the isoclines of two species plotted as a function of the density of species 1 (N_1) and the density of species 2 (N_2). Show with the use of arrows and vectors the joint movement of both populations for each region of the graph (each region is defined with reference to the isolines). Then describe, with reference to the isoclines, why the joint movement in each region is the way it is (why the arrows point the way they do). State what the outcome of competition is in this system (name the outcome and also show on the graph where the population will eventually stabilize). Illustrate, by drawing lines from the equilibrium point to each axis, the equilibrium population sizes of N_1 and N_2.

* refer to final diagram 84 Underneath both isoclines, the vector points diagonally to the right and up, indicating that both populations are increasing. Underneath species 2 isocline, but above species 1 isocline, the vector points diagonally to the left and up, indicating that species 2 is growing, but species 1 is declining. Above both isoclines, the vector points diagonally to the left and down, indicating that both species are declining. The outcome here is species 2 wins and species 1 goes extinct.

In class, we modeled competition where both species have a negative impact on the other (i.e. both a and B > 0). However, experiments have shown that competition can be asymmetrical, with one species affecting the other, but not vice versa. In this case, one of the competition coefficients would be 0. What would the isoclines look like for a situation where we have stable coexistence, where species 2 affects species 1 (a > 0), but where species 1 does not affect species 2 (B = 0)? Redraw the stable-coexistence case (shown in question 4) to illustrate this new case. You can figure out the answer for this question for first principles (i.e. work through the equations for the isoclines an see what happens when (B = 0).

* refer to final diagram 86 The isoclines would still follow the regular stable-coexistence crossing (where species 1 above species 2 on left), but vectors will be different. Species 2 will always be growing, thus, illustrating no negative effect from species 1, while species 1 will have normal arrows. So, while the isoclines look the same, the vectors will always either point diagonally left and up or diagonally right and up.

The equilibrium theory of island biogeography can explain why both island size and isolation affects the number of species found on an island. Using graphs, show the basic idea behind this model. Explain clearly in words the reason why extinction and colonization rates show the relationships they do with number of species on an island (i.e. why they show negative or positive slopes). Also explain fully why it is an equilibrium model of diversity (i.e. what happens if they number of species is above or below the equilibrium number of species). For an island that is at the equilibrium number of species for a long period of time and we examined the specific species present, would our list of species remain constant across visits? Why or why not?

* refer to finals diagram 121 Based on the graphs, as area (or island size) increases, the number of species increases (positive slope). As the number of species increases, the immigration rate decreases (negative slope) and the extinction rate increases (positive slope). The immigration rate decreases because, as the number of species increases, the number of available niches decreases leaving no space for new colonizers. The extinction rate increases because, as the number of species increases, niches begin to overlap and interspecific competition ensues. When you put both the immigration rate and extinction rate graphs together, you get an equilibrium model of diversity. The point where the two lines intersect is the turnover rate, where there is a change in species composition because extinctions are balanced by immigration. When the number of species is above the equilibrium number of species, the extinction rate increases and the immigration rate decreases. When you are below, it follows the same pattern, but less dramatically. If you include island size in the equilibrium model, the model predicts that larger islands have more species because the extinction risk per species decreases due to the larger population size. For an island that is at the equilibrium number of species for a long period of time, our list of species would not remain constant. There would still be extinctions and immigrations occurring even at the equilibrium. Equilibrium just means that for each species that goes extinct, a new immigrating species will arrive to take its place.

Modeling has also taught us that the behavior of predators can stabilize population dynamics, particularly with respect to the efficiency with which individuals capture individual prey and how this changes with prey density. This relation between rate of prey capture per predator and prey density is called the functional response. With graphs, illustrate the three types of functional responses (I, II, and III; in predator-prey context). Show the corresponding relationships when these are graphed in terms of proportion of the prey population consumed, instead of the number of prey consumed per predator. With these second graphs, explain with reference to density dependence why a type III functional graph can stabilize prey populations (i.e. why predators can impose density-dependent mortality that brings the prey population to an equilibrium). Describe two mechanisms that can produce a type III functional response.

* refer to finals diagram 95 The reason why a type III functional graph can stabilize prey populations is that it is the only functional response than can impose density dependent controls of the prey population (as you can see from the graphs, because it is the only functional response that hits carrying capacity and stabilizes BOTH times). Two of the mechanisms that can produce a type III functional response are hiding spots, which allow prey to hide and there is only so many available thus it is a density-dependent resource, and prey switching in search image predation, where the predator focuses on the most common prey available so they keep competition between different prey species in check.

You have just completed your study of a cohort of your favorite organism, the wrinkle. You have compiled all of your data and found that of the original 100 newborns you followed, your summaries show that 80 survive to year 1 where they had (on average) .5 babies each, 50 survived to year 2, where they had 1 baby each, and none survived to year 3. Build a life table with these data and show whether the population is stable, decreasing, or increasing.

*refer to final diagram 64 Growing.

The following survival and birth data were obtained for an original cohort of 1000 individuals of a rare mouse, the Squishy Furball. Fill in the table and show whether this population is declining, stable, or increasing. Explain in words why the value of the variable you have calculated, R_0, tells us if the population is growing, stable, or decreasing. That is, what exactly does R_0 represent anyway. What do the terms I_x and I_x*b_x mean and why does their summed value R_0 tell us whether the population is changing or not across generations? Finally, how doe R_0 differ from or lambda?

*refer to final diagram 65 Increasing. R_0 is growth rate per generation. If R_0 is greater than one, the growth rate is greater than one, and thus the population is growing. I_x means the proportion of the original cohort that is still alive at age x. I_x*b_x is that times the number of babies per female at age x. This would give you a number that represents the growth rate of a generation each year. And summing the growth rate for each year would give you the growth rate for the entire generation, R_0. This can be used to tell us whether the population is changing or not across generations because it sets the stage for future generations (each baby born to each female) as well as still telling us how many individuals there are alive in the population (number of survivors each year). Based on these, you get a pretty good idea of whether the population is surviving at a healthy rate and if they are producing enough offspring to grow. R_0 differs from lambda because lamda is a discrete growth rate, while R_0 is continuous.

You assemble life tables for two species, A and B. When you calculate R_0 based on the life table you find that both species have the same R_0. However, the populations are not growing at the same rate. Explain with reference to generation time, G, why we see this difference. What is generation time? Which population will have the faster growth rate and why?

*refer to final diagram 66 We see this difference because species A becomes sexually mature earlier than species B. Generation time is calculated as the sum of I_x*b_x*x divided by R_0 and is defined as the average age of the mother and babies born in the life table. Species A, while they have less babies on average than species B, reproduces after one year of age while species B does not reproduce until two years of age. Therefore, it takes less time for more babies to be born in species A, thus the population grows faster.

The evolution of clutch size in birds played a central role in the development of modern life history theory, largely due to David Lack's ideas about adaptive clutch size (number of eggs a bird lays in its nest). What was Lack's idea? Propose an experiment you could perform to test this idea. Describe or show graphically what result would support Lack's hypothesis, and what would reject it. If your experiment rejected Lack's hypothesis, as many experiments have down, two important life history trade-offs could be at play. What are these important trade-offs? What additional data would you need to collect from your proposed experiment (i.e. new factors to measure that Lack ignored) to test for each of these trade-offs?

*refer to final diagram 73 Lack's principle states that "the clutch size of each species of bird has been adapted by natural selection to correspond with the largest number of young for which the parents can, on average, provide enough food". You can experimentally manipulate clutch sizes by adding or removing eggs from nests and seeing how many offspring survive on average for each number of eggs in the nest. Essentially, the parents should be able to take care of all their offspring up until a certain point and then survivorship will decline rapidly. On a graph, if Lack's hypothesis was correct, this would follow an upside-down U parabola when you have offspring survivorship on the y-axis and clutch size on the x-axis. If Lack's hypothesis were incorrect, it would not follow this curve as measuring offspring survival to parental independence is not a good measure of fitness. The two important trade-off Lack's hypothesis fails to account for are: 1. size vs. number of offspring: parents with bigger broods might have weaker offspring with reduced long-term survival 2. present vs. future reproduction for parent: if you force parents to raise larger than optimal clutch sizes you may reduce the adult's survival or reduce future fecundity. To test for these trade-offs, you would need to measure average size of offspring to make sure the broods are not weaker to begin with and you would need to measure parent's fecundity over time.

What is an "isocline"? Draw and identify prey and predator isoclines on a phase diagram of prey and predator population size for the basic Lotka-Volterra predation model (i.e. NOT competition). Identify the joint equilibrium. Any nudge of the populations will produce stable limit cycles. For such a situation, show using thin arrows for the change in each species numbers on each side of their isocline. Use fat arrows to show the joint movement of predator and prey numbers.

*refer to final diagram 92 An isocline is a line on a diagram or map connecting points of equal gradient or inclination.

mutualism effects

+ and +

consumer-resource effects

+ and -

detritivore-detritus effects

+ and 0

The antagonistic coevolution between Heliconius butterflies and Passiflora vines (passionfruit) has lead to some very interesting defenses that the plants use to reduce the risk of herbivory by butterflies. What are these defenses and how do they work.

- Incredible variation in leaf shape among passiflora vines (butterflies use visual cues to select host plants - Egg mimicry: butterfly females often avoid plants that have eggs; plant leaves have fake eggs - Plant has extrafloral nectaries to attract ant bodyguards - Fatal velcro: zillions of sharp curved hairs that trap and kill baby caterpillars

K-selected species

- Live in more stable habitats - Populations grow slowly and can be declining - Few offspring - Large offspring - Long time to maturity - Strong intraspecific competition

r-selected species

- Live in unstable habitats, disturbance keeps populations way below K - Populations always growing - Favored are traits that permit rapid population growth - Lots of offspring - Small offspring - Short time to maturity - Weak intraspecific competition

What is the optimality approach to life history?

- Trade-offs are important - Mortality patterns are critical

competition effects

-(0) and -

Describe three examples of mutualisms. For each example show how each participant benefits.

1. Cleaner shrimps and tiger groupers: the cleaner shrimp feed off dead tissues on the groupers and the groupers get cleaned and sanitized in return. 2. Honeyguides and humans: the human whistles to attract a honeyguide and the honeyguide guides them to a beehive. The human benefits from an increased rate of finding bee nests--and honey--and the honeyguide gets increased access to the wax in return. 3. ant acacia and ants: acacia provides the ants housing and food and the ants provide protection by pruning competitor plants and killing herbivores in return.

Name four types of interactions between species.

1. Competition 2. Consumer-resource (predation, herbivory, parasitism) 3. Mutualism 4. Detritivore-detritus (food is dead)

***What are three possible outcomes of competition in the real world (2 ecological, 1 evolutionary)? What patterns would each outcome be expected to produce if you were looking for evidence? For the ecological outcomes, describe a general experiment and predicted results that would support each outcome.

1. Ecological: One possible outcome is coexistence where species all occupy a niche and survive without leading to competitive exclusion. You would want to see different species using the same resources without one species outcompeting the other. 2. Ecological: One possible outcome is competitive reversal where a lesser species in one habitat is the superior species in another. 3. Evolutionary: One possible outcome is competitive exclusion where one species drives another species to extinction because it is a superior competitor.

Three different mechanisms of succession differ in whether species interactions affect the outcome of succession, and whether all species can establish after a disturbance. Outline the key differences between Facilitation, Tolerance, and Inhibition mechanisms.

1. Facilitation - Only pioneer species can tolerate early conditions - Pioneers modify habitat - Then later stages can establish ` 2. Tolerance - No pioneers, all species can establish - Stable equilibrium reached when no species exists that can invade - So could have r-type and K-type species that affect sequence 3. Inhibition - Any species can establish - Early inhabitants make habitat less suitable for other species

What is the problem with r- and K- selection?

1. Most species don't fit cleanly into r or K 2. No relation to life tables and specific population and fitness aspects. 3. For K-species, density dependence as a driver is never shown.

Evidence that herbivory has negative fitness consequences for plants comes from the ways that plants defend themselves against herbivores. What are three general defenses plants can use to reduce the risk of herbivory?

1. Physical defenses such as spines. 2. Plants have secondary plant compounds--coffee, drugs, spices--that deter herbivores. 3. Plants will develop chemical defenses to deter herbivores from eating them, such as the bitter flavor of unripe fruit not developed enough to be spread by herbivores yet.

The Lotka-Volterra models tell us what happens when competing species are able to reach equilibrium (both K's are reached). However, there are reasons why equilibrium might not be reached, so that the model does not apply. What are two of these reasons? Can you provide an example of each type?

1. Predation 2. Disturbances (fire, waves, drought, etc.) An example of predation is pisaster (the sea star) that lives on the Washington coast. It is a top predator and eats barnacles, chitons, and mussels. In an experiment, pisaster was removed and they compared species present in removal versus control plots. In removal plots, with no sea stars, mussels take over an outcompete the other prey which reduces biodiversity. In the control plots, there existed 15-18 different species. Therefore, pisaster is a keystone species, who increases species richness and keeps mussels under control. So, predation is an example of why equilibrium might not be reached because sometimes if predation is removed, competing species quickly outcompete each other and never reach equilibrium. An example of disturbance is that a disturbance knocks out superior competitors and fugitive species, who have fast life histories, take advantage of the open space before the superior competitors grow back. A specific example is the sea palm postelsia that grows in the surf zone on mussel free rock patches cleared by waves. Postelsia is an annual with a super fast life cycle and high fecundity. Thus, disturbance is an example of why equilibrium might not be reached because the competing species is always being removed, so there is no chance for equilibrium.

Name three life history trade-offs.

1. Size vs. number of offspring 2. Reproduction vs. adult survival 3. Grow vs. reproduce

Why should ecologists and conservation biologists care about metapopulations? Discuss three implications of metapopulations to ecologists and conservation biologists.

1. Spatial structure matters. - Looking at local population dynamics will not be sufficient for understanding the system - We need metapopulations to gain an understanding of these spatial dynamics. 2. Implications for species interactions. - For example, Lotka-Volterra competition models - Local populations might predict competitive exclusion - Global populations might predict coexistence if a weak competitor is a good disperser - We need metapopulations to understand the implications of species interactions. 3. Habitat loss can increase extinction loss - With fewer patches overall, absolute number occupied decreases, which increases the risk all go extinct - Each patch is farther from the others, on average, so dispersal is less successful. - We need metapopulations to prevent extinctions.

There are many ways that animals can potentially reduce the risk of predation (as demonstrated in the slide show). List four of these possible mechanisms. For one of these mechanisms, outline an experiment you could conduct to test whether the mechanism is actually operating in a species, and clearly identify the result of your experiment that would support the hypothesized mechanism.

1. aposematic coloration: bright colors to advertise danger or distastefulness; warning coloration (e.g. butterflies, coral snakes) (often associated with Batesian and Mullerian mimicry) 2. chemical defense: many insects sequester noxious chemicals; often have bridget colors to advertise (i.e. they have aposematic coloration) 3. feigning death: some predators will not eat carrion, so faking death may cause a predator to lose interest (e.g. Darwin's frog laying on back exposing brightly marked belly) 4. armor and spines: armadillo with defensive plating; porcupine with quills To test for aposematic coloration, you can take a brightly colored species (like a monarch) and put it in an environment alongside more dull colored species. You would then monitor predation and see if the predators target the brightly colored monarchs. If the experiment supported the mechanism, predators would avoid the monarchs and eat the other butterflies.

The nature and consequences of interspecific interactions is a central focus of ecology. Name three types or categories of interspecific interactions between interacting pairs of species; these can be distinguished on the basis of how each species affects the other (0, +, -). Discuss one ecological consequence (e.g. population process) and one evolutionary consequence (e.g. adaptive response) that would be expected from each type of interaction.

1. competition - Effect on species 1: - (0) - Effect on species 2: - - Ecological consequence: if they compete with one another, density-dependent mechanisms may begin to occur as the resources begin to get depleted - Evolutionary consequence: If competition continues, natural selection begins to take affect and the species or individuals best suited to collecting resources will survive 2. predation - Effect on species 1: + - Effect on species 2: - - Ecological consequence: predator-prey models may begin to emerge where their populations volley back and forth in success - Evolutionary consequence: both predator species and prey species will evolve adaptations in relation to each other to make them either better and hunting the prey or evading the predators 3. mutualism - Effect on species 1: + - Effect on species 2: + - Ecological consequence: both populations will benefit and experience growth - Evolutionary consequence: sometimes they may develop adaptations alongside one another to make the mutualistic relationship even more successful such as evolving sweet scents to attract pollinators

What is meant by metapopulation? Metapopulation theory predicts that under certain conditions, an equilibrium can be reached where a stable fraction of patches (P) is occupied. In theory, what two factors does P depend on?

A metapopulation is a group of populations that are separated by space but consist of the same species. These spatially separated populations interact as individual members move from one population to another. The two factors P depends on are: 1. Population size --> smaller populations are more likely to go extinct 2. Variation in population size

Fill in each graph below with the curve or lines predicted by the equation or phrase at the top of the graph beside the large letters. For graphs that you intend to draw a straight line, please write "straight" besides the line since it is sometimes hard to tell what you have drawn. A. Type III functional response y-axis: proportion of prey population consumed (i.e. RATE) x-axis: prey density (N) B. Type II functional response y-axis: # prey consumed/individual predator x-axis: prey density (N) C. Lack clutch size (predicted) y-axis: # offspring surviving to independence (fledging) x-axis: experimental clutch size (reduced, normal, enlarged) D. Offspring size vs. number trade-off y-axis: # offspring surviving to next year x-axis: experimental clutch size (reduced, normal, enlarged) E. Type II survivorship curve y-axis: natural log (ln) N x-axis: Age (or time) F. Stable limit population cycle y-axis: N x-axis: time (t) G. Species area curve y-axis: Log number species x-axis: Log area H. Type I survivorship curve y-axis: natural log (ln) N x-axis: age (or time)

A. Upside-down U B. L but curved and rotated 90 degrees to the right C. Upside-down U D. Straight negative sloping line E. Straight negative sloping line F. Sinusoidal curve going up and down G. Straight positive sloping line H. J but rotated 90 degrees to the left

You have just completely your study of a cohort of your favorite organism, the Fuzzy Spreader. You began your study by ear-tagging 1000 newborn females, followed the entire cohort until the last one died, and noted the number of babies each female produced, on average, at each age. You just compiled all of your data and found the following: of the original 1000 newborns (i.e. age 0) you followed, 700 survived to year 1 where they had (on average) 1 female baby each, 100 survived to year 2, where they had 3 female babies each, and none survived to year 3. Is the population growing, declining, or stable? To answer, complete the life table, calculate R_0 and explain your answer in terms of the value of R_0.

Age: x, 0, 1, 2, 3 Number alive: n_x, 1000, 700, 100, 0 Female babies/adult female: b_x, 0, 1, 3 I_x, 1.0, 0.7, 0.1 I_x * b_x, 0, 0.7, 0.3 R_0 = E(I_x * b_x) = 1.0 It is stable because R_0 = 1.0.

life table

An age-specific summary of the survival pattern of a population. - are about births and deaths, by age - we tag individuals to look at births and deaths across age - when to mature? - how many babies to have? - care for babies or not? - reproduce once or many times? - stop growing when sexually mature or keep growing? - annual or perennial? - used to look at age-structure populations

As victims of infectious disease and parasites we often focus on the symptoms from our own perspective (i.e. the bad consequences of the disease to us or other organisms). However, many symptoms of disease make sense in terms of adaptations of the parasite or disease to increase its rate of spread from host to host. Provide an example of this and explain how the symptom might work to increase the fitness of the disease.

An example of this is the coughing symptom. To us, we dislike it because it can hurt and otherwise is a nuisance to us and others around us. However, by making us have to clear our throats, the disease is able to have us eject bacteria or viruses out at fast speeds. If we are around other people, these bacteria or viruses can quickly find a new host when they end up inhaled or on the skin of the new host. This increases the fitness of the disease because it is difficult for us to stifle a cough, thus it creates an easy and surefire way for the disease to transfer quickly through small interactions among a species.

Many plants have clear mutualistic relationships with plants. Dan Janizen's work with ant-acacia trees in Costa Rica shows this nicely. How do the ants benefit from their association with the plants? What benefit do the plants gain from having an association with the ants?

Ants benefits from: - Receiving housing - Eating plant Beltian bodies for protein - Eating plant nectar from extrafloral nectaries Plant benefits from: - Ant protection through: 1. Pruning of competitor plants 2. Killing herbivores

The box below shows four species of snakes, each identified by its own letter. The snakes vary in their markings, which provide some sort of visual signal, and in their toxicity as well. Snakes with smiles are harmless; those with frowns are poisonous. The background pattern inside the box is the background on which predators would look for the snake. Identify one snake in the picture below that fits each of the following descriptions and fill in the letter of the snake next to the description: Mullerian mimic _____ Batesian mimic _____ Cryptic coloration _____

B or D A C

Evolutionary biology tells us that there is no fountain of youth. Evolutionary explanations for senescence (aging) focus on patterns of "extrinsic" mortality and the likelihood that any individual will live to an old age ("extrinsic" is mortality due to external factors, not due to trade-offs intrinsic to the organism). Explain the GENERAL evolutionary hypothesis for aging in the context of life history theory, specifically with reference to survivorship. Then provide two more specific explanations in terms of (i.) accumulation of mutations that act late in life as opposed to early in life and (ii) trade-offs between genes that are expressed early and late in life.

Because aging increases an organism's vulnerability and likelihood of mortality, it is in contradiction with Darwin's theory because shouldn't species be evolving away from increasing mortality and decreasing reproductive capacity? The general evolutionary hypothesis for aging is that extrinsic mortality (outside affects that do include aging) drives timing for deleterious genes. The idea is that, for a given life table, at some age there will be very few individuals still alive. Late acting genes that affect very few individuals, and increase mortality, are under very weak selection as these individuals likely do not produce many offspring, if any. So, survivorship of aging individuals is isn't really acted upon by natural selection, so aging continues. i. The mutation accumulation theory suggests that there is only weak selection against late acting genes, so they accumulate and are passed on regardless of whether they make the individual more fit. ii. The antagonist pleiotropy theory suggests that genes that once beneficial early in life may be costly later in life as one gene may have more than one trait.

What is the major limitation of the theory of island biogeography in terms of why it might not apply to the mainland or to large islands?

Because larger islands or the mainland tend to have more species, there is a greater chance that you will have species that is more extinction prone or you will experience massive variation in dispersal among species. The theory can be too simple to be applied to larger areas.

Destruction of habitat like forests often leaves islands or patches of suitable habitat in a sea of unsuitable habitat. This is often the case when we set aside chunks of forest habitat as reserves or parks. Ideas from both metapopulation theory (for single species) and the theory of island biogeography (for entire communities) has lead to a discussion over the design of reserves: for a given total area to be preserved, is it better to save a Single Large Or Several Small reserves, the so-called SLOSS debate. What are the benefits of creating a single large reserve and what are the benefits of creating several small reserves? Justify each benefit in terms of metapopulation theory, island biogeography theory, or other ideas learned in the course pertaining to populations or communities.

Bigger better: - More habitats in reserve, will have more total species (beta diversity higher) - Higher densities top predators; less likely to go extinct and have trophic cascades - Bigger populations of each species, on average, less inbreeding depression - Bigger populations of each species, more genetic variation, more potential for natural selection - Bigger populations of each species, less risk of extinction from stochasticity - Lower ratio edge/forest, lower predation risk or parasitism by edge species Smaller better: - More habitats saved in sum of reserves when habitat widely separated geographically, will have more total species (beta diversity higher) - Avoid putting all eggs in one basket and suffering catastrophe with disturbance or disease

The common cuckoo and the songbirds they parasitize in Europe provide convincing evidence that co-evolution has shaped traits and behavior seen in cuckoos and their hosts. Explain what is meant by coevolution and outline the hypothesized co-evolutionary process that has taken place between cuckoos and their hosts, being sure to identify traits of hosts and parasites and their role in coevolution.

Co-evolution occurs when two interacting species cause reciprocal evolution in each other: species A harms B, B then evolves traits to reduce the impact of A, B's newly evolved trait harms A, which causes natural selection in A, and so forth... In Europe, we see currently see different genetic strains of cuckoos, each specializing on parasitizing different host species and laying eggs that mimic the eggs of their hosts. Co-evolution is thought to have produced this pattern as follows. We assume that initially there was a generalist cuckoo that parasitized many species of hosts, that these hosts were "naive" and accepted any cuckoo eggs, regardless of their appearance (i.e. no mimicry yet). Step 1: Cuckoo parasitism is very costly for hosts, since the cuckoo chick kills all of the hosts' chicks; these costs lead to natural selection for host behaviors to reduce these costs. Step 2: Evolutionary response in hosts. We see the evolution of egg recognition and rejection hosts, who reject eggs that are sufficiently different in appearance from their own eggs. Step 3: Counter-evolution in cuckoos. Egg rejection by hosts reduces the fitness of the cuckoo, which is still a host generalist brood parasite. Egg rejection causes natural selection for egg-mimicry by cuckoos, which at the same time requires the evolution of host specialization (since eggs of different hosts vary, an individual female cuckoo cannot simultaneously mimic lots of different hosts and she must lay her egg in a host species with eggs similar to her own so that the match is good (mimicry).

Data for survivorship curves can be extracted from life tables. When the logarithm of n_x is plotted as a function of age (time), ecologists note three basic types of survivorship curves: I, II, and III. Draw the three types of survivorship curves, pointing out what each curve means in terms of early versus late survivorship. Provide a real example of each.

Curve I has a high survivorship early and middle in age, and a high mortality rate when old. An example of these are humans, where there is low mortality up until around 80 where we reach a steep drop-off in survivorship. Curve III is the opposite of curve I. A high mortality early on in age, however, as individuals age, their survivorship increases. An example of this is fish or plants. Curve II is the intermediate between I and III. There is a relatively equal rate of mortality throughout life. An example of this is birds after they reach adulthood.

antagonistic pleiotropy theory

Genes that are beneficial early in life, but have costs late in life.

Distinguish between "interference competition" and "exploitative competition" and give a biological example of each. (This was covered earlier in intraspecific competition and density-dependence).

In interference competition, an organism will use defenses or resources to prevent other organisms from using the resource. In other words, they will INTERFERE with the others ability to acquire resources. An example of this is neighboring coots defending their territory border using their talons or even just mussels taking up space on a rock and preventing other mussels from using that space because there just isn't any let. In exploitative competition, which is more common, organisms use up resources directly. Once used, the resource is no longer available for other species to use. In other words, one species will EXPLOIT all the resources, so there are none left over. An example of this occurs in nearly any population or group of species that experiences food scarcity. Some organisms or one species will use up all the resources directly, leaving none for the others.

Why does the value of R_0 tell you whether the population is stable, increasing, or decreasing (in other words, what does R_0 represent biologically)?

It is the total (lifetime) number of female babies born, on average, to each female that enters into the table in the first cohort. If it is greater than one, we have more than one baby next generation for each baby this generation; i.e. population growth.

In many taxa, species richness (i.e. the number of species in area) shows a striking relationship with latitude. What is this pattern? Describe four hypotheses than can potentially explain why species richness increases as one heads towards the tropics from the poles. Explain specifically the logic of each hypothesis--i.e. specifically how does hypothesized mechanism explain the change in species richness with latitude.

Latitudinal gradient in species richness --> more species as you head from either pole to the equation 1. There may be more species due to diet specialization. As you get closer to the equator, there is also more diversity in plants and insects, so you would have more animal species. 2. There may be more because there is more solar energy received around the equator, allowing for greater species richness because conditions are easier to survive in than the cold. 3. Tropics are the largest and oldest biome, so it makes sense that there would be more species around the tropics or the equator. 4. Fairly consistent temperature and humidity compared to the poles.

Aposematic warning signals will only work to reduce predation if the predator somehow recognizes that the signal means "nasty, do not eat me." How predators know to respect warning colors (i.e. the mechanisms that enable them to recognize the signal) are expected to differ for predators of prey that are simply unpalatable (as with blue jays eating monarchs) compared to potential predators of lethal prey (as in birds (motmots) that might eat coral snakes. Describe a mechanism that could be used for recognition with unpalatable prey and one that could be used for lethal prey, and explain the logic of why these mechanisms would need to differ.

Learning: for unpalatable prey since predator gets mildly sick, but lives to recall the bad encounter and learns to remember the signal Innata or Instinct: for lethal prey since there is no way the signal can be learned: a single encounter kills the predator, and dead predators cannot learn

Name three life history traits. Name three important life history trade-offs.

Life history is the series of changes undergone by an organism during its lifetime. Traits include: 1. optimal clutch size --> how many babies should you have 2. annual vs. perennial --> should you live for one season or longer 3. when to mature --> should you mature early or later (these often correlate with r or k selection --> patterns in the life histories for organisms) Trade-offs include: 1. size vs. number of offspring --> should you have big babies like elephants or a bunch of tiny ones like mice? pros and cons? 2. reproduction vs. adult survival --> should you have dazzling colors to attract your mate or do you want to stay safe from predators? pros and cons? 3. grow vs. reproduce --> do you want to keep growing or should you invest that energy into babies? pros and cons?

Senescence is the pre-programmed deterioration in performance as an organism increases in age: it is produced by genes that have nasty effects on the organism only later in life, not early. Life history theory provides an evolutionary explanation for why genes with nasty effects late in life might accumulate in populations, or even be favored by natural selection. Outline the basic idea, with reference to life tables, mortality, and the relative numbers of individuals expected to be in different age classes.

Life table analysis illustrates that with some "extrinsic" mortality (i.e. not due to senescence) there will always be more young individuals than old individuals in a stable population. Thus, even without any senescence, there will be a few really old individuals due to extrinsic mortality. Thus, nasty genes that act late in life affect few individuals, in contrast to genes that act early in life. There are two reasons why late-acting genes might accumulate in populations. First natural selection is very weak against nasty late-acting genes because they affect so few individuals, so they might just accumulate. Second, pleiotropic genes (i.e. genes with two different effects) that have good affects early in life but nasty effects late in life have a net positive effect on fitness because more individuals get the positive effects than the late nasty effects; natural selection could favor such genes. Note that with senescence, there are two sources of mortality; extrinsic and intrinsic. This is illustrated by the ringed seal mortality data which shows a constant baseline mortality (extrinsic) with a sudden increase in mortality after reproduction begins (intrinsic mortality; i.e. senescence).

Mullerian and Batesian mimicry have different sorts of dynamics in terms of whether we expect a long-term stable signal to evolve or a less stable dynamics where selection favors one species to move away from the other. Explain. Related to this, explain why frequency-dependent selection (i.e. when fitness depends on the frequency of different types) is particularly important in systems with Batesian mimicry.

Mullerian mimicry is mimicry where the appearance of two or more unpalatable species converge. In other words, convergence of the same specific aposematic coloration pattern among more than one species. In terms of dynamics, we can expect a long-term stable signal to evolve that tells predators that these species are all unpalatable (making this a mutually beneficial convergence). After a predator first tries an unpalatable species and has a bad experience, they will recognize the color pattern in the future. This recognition can even evolve to be innate and long-term information passed down genetically. On the other hand, batesian mimicry is mimicry of an unpalatable species by a palatable species. In terms of dynamics, this is less stable and selection favors one species to move away from the other. By parasitizing the honest warning signal of the model (the species being mimicked), the Batesian mimic gains an advantage, without having to go to the expense of arming itself. The model, on the other hand, is disadvantaged, along with the predator. If imposters appear in high numbers, positive experiences with the mimic may result in the model being treated as harmless. Thus, selections begins to favor one species moving away from the other. Additionally, at higher frequency of models and mimics, there is also a stronger selective advantage for the predator to distinguish mimic from model. For this reason, mimics are usually less numerous than models, an instance of frequency dependent selection, where fitness of a phenotype depends on its frequency relative to other phenotypes in given population. In negative frequency-dependent selection, the fitness of a phenotypes decreases as it becomes more common.

Are predators always bad for potential prey populations? (By potential prey, I mean things the predator could eat but does not necessarily eat. Hint: the sea star removal experiment provides the answer.)

Predators are not always bad for potential prey populations and contrary, they can actually increase species richness. This is because some predators are keystone species. In the example of pisaster, a sea star, in an experiment where two plots were set up, a control plot and a plot with no sea stars, the plot with no sea stars became overrun with mussels, one of the primary prey of sea stars, and all the other prey species were eliminated. While in the control plot, there were 15-18 more species present.

R_0 is not the same as lambda or r. How does it differ?

R_0 denotes population change on a per generation time (G) rather than on a fixed time unit.

Island biogeography has been used to think about how we should design nature reserves, because such reserves are often islands of pristine habitat in a human altered landscape. This lead to the S.L.O.S.S. debate: for a given size of area to be preserved, is it better to make a Single Large Or Several Small reserves? Discuss some of the factors that will influence this decision.

Single large? - Best to conserve top predators because they have huge home ranges --> if too small, predators disappear which leads to trophic cascades - Less edge effect --> edges of forest often poorer quality habitat in terms of light, moisture, predators, etc, so a large island has larger fragments which have a lower proportion of edge habitat - Bigger --> larger population sizes, therefore less extinction --> more species --> species area effect - Genetic diversity (evolvability) Several small? - Insurance against disaster - Marine systems --> dispersal and metapopulation structure matters - For migratory organisms, one might need global coordination so migrants have winter and breeding habitats - Habitat diversity and species ranges

The theory of "r-and-K selection" is a habitat-based view of life history, where "habitat" refers to the ecological factors that affect whether or not species are at their carrying capacity. Name some life history traits associated with an r-selected species and with a K-selected species. What is the basic difference between an r-selected and K-selected life history in terms of causal mechanism (hint: think about the two types of population models for unlimited growth versus density-dependent growth)? One of the problems with r-and-K selection is that the assumed causal mechanisms are never demonstrated. Describe an experiment that would allow you to test for the proposed causal mechanism is a K-selected species.

Some life history traits associated with r-selected species are that they have many offspring, their offspring are small, they mature quickly, and there is not much intraspecific competition. Some life history traits associated with K-selected species are that they have few offspring, their offspring are large, they mature slowly, and there is strong intraspecific competition. The basic difference is that r-selection species populations grow fast and hit carrying capacities early on, while K-selected species grow more slowly, as they are experiencing density-dependent growth continually. To test for the proposed causal mechanism in a K-selected species, you can conduct a density-dependent experiment based on intraspecific competition. You can set up two plots. In the first plot, you provide a stable amount of food and allow the population to grow and record birth and death rates. If the population hits a carrying capacity and evens out, you have intraspecific competition. In the 2nd plot, you vary the amount of food (more or less) and record the new population sizes (and birth and death rates). If the population sizes vary based on the amount of resources available (food), you have intraspecific competition. This would demonstrate the causal mechanism of K-selection, as r-selected species should experience weak intraspecific competition.

The two life tables below are for two different species. Based on life history theory--specifically the evolutionary explanation for aging--explain which species will have an earlier onset of aging (senescence). Hint: you don't need to do any calculations, you can figure it out just looking at the table. Species A: Age: X, 0, 1, 2, 3, 4 Number Alive: n_x, 1000, 500, 250, 100, 0 Babies/female: b_x, 0, 0, 2, 5, 0 Species B: Age: X, 0, 1, 2, 3, 4 Number Alive: n_x, 1000, 400, 100, 50, 0 Babies/female: b_x, 0, 2, 1, 2, 0

Species B will have earlier onset of aging because they mature earlier. Generally, those with higher annual survival have a later maturity. So, because B reproduces earlier in life, they mature earlier in life, and will age earlier in life.

demography

Study of age structure in populations.

R_0

Tells us how fast a population is changing per generation (not per year). - If R_0 = 1 --> stable - If R_0 > 1 --> growing - If R_0 < 1 --> declining - Per year growth is lambda or r, not R_0 - Generation time matters

At times, it can be difficult to distinguish predation (and other harmful interactions) from mutualism. Show that this is so by describing predation on conifer seeds by birds that cache the seeds for the future (i.e. smart birds like blue jays bury the seeds and return to find them at a later date).

The blue jays prey on trees by eating their seeds. However, this can actually be mutualistic for the tree, as sometimes the seeds will begin to grow after being buried by the blue jays. So, sometimes blue jay predation turns into a mutualism and the blue jay can enjoy more seeds in the future.

When generation time, G, is estimated, how can one convert the population growth rate per generation, R_0, to the intrinsic rate of population change, r?

The intrinsic rate of increase, r, of the Malthusian parameter, can be used to calculate the rate of increase in populations that reproduce within discrete time intervals and possess generations that do not overlap. Simply put, it is the number of births minus the number of deaths per generation time or the reproduction rate minus the death rate. To convert R_0 to r, you take the natural log of R_0 divided by G. r = ln(R_0)/G

On your trip to Alaska you discover a lemming that shows dramatic and regular population fluctuations. Two different mechanisms could account for these fluctuations, one involving interactions among species, one involving interactions within species. Describe these explanations and what you could do to distinguish between them.

The mechanism that could account for these fluctuations involving interactions among species is prey switching in search image predation. As the lemming population grows, they become the most common prey species. Predators begin to target them as they show up more often and thus, after the lemming population grows, it will begin to fall dramatically as predators focus in on them until the population falls and a new prey species becomes the target. The mechanism that could account for these fluctuations involving interactions within species is hiding spots. As the lemming population grows, territory becomes more competitive and the number of hiding spots the lemmings can retreat into declines as more and more lemmings begin to take the hiding spots in the growing populations. Individuals who can't find hiding spots, as they have all been taken, become easy pickings for predators. So, when the lemming population increases, the number of hiding spots decreases, leading to more predation which then decreases the population density dramatically. To distinguish between these two mechanisms, you could first conduct a search image predation experiment with members of the predation population.

What is the most important basic conclusion from the simple models like Lotka-Volterra and the one you examined in the lab with respect to the influence of predation on simple predator-prey systems? Do laboratory studies support or refute this conclusion?

The most basic conclusion is that populations are prone to destabilization if predators over-exploit prey, but predation may also facilitate prey coexistence depending on the predator preference and competitive interactions among prey species. Yes. Laboratory studies seem to support this, as they most often result in extinction over a short time (thus, destabilization is common). This perhaps indicates the importance of refuges from predators in natural systems.

A critical question in ecology is whether populations are limited by what they eat (bottom up) or by what eats them (top down). The answer, in some cases, depends on the number of trophic levels in the system. Discuss, with reference to the kelp-urchin-otter system, how the number of trophic levels influences community structure in kelp forest communities. Provide evidence in terms of recent reductions and additions of trophic levels to the community in different parts of the geographic range of sea otters.

The number of trophic levels in a food web can have a huge impact on the the degree to which plants (or other primary producers like kelp) are limited by nutrients that enter the system from below (bottom up) or are limited by herbivores from above (top-down regulation of plants). In California, the normal kelp community is a three trophic level system--otters eat urchins (and other invertebrates), which in turn eat kelp. In this three level system, urchins are controlled by otter predation rather than by resources (kelp). Urchin numbers are low enough that so that kelp populations are limited by resources (nutrients and light), not herbivory. Kelp is thus plentiful. In the past, otters were removed from the community through human harvest. This converted a three level community to a two trophic level system, where urchins were no longer regulated from above but became limited by their food (kelp). Intense urchin herbivory greatly suppressed kelp abundance, leading to "urchin barrens" with tons of urchins but little kelp. Recently in Alaska, a fourth trophic level has been added--killer whales have begun preying on otters, which have become very rare. This has had the same effect as the removal of otters by humans, and this four level system has also resulted in urchin barrens where urchins are everywhere and kelp is scarce.

It was originally thought that diseases would always coevolve with their hosts to become progressively more benign. However, recent evolutionary insights show that this is not always true. Discuss the evolutionary theory of disease virulence and the evidence that supports this theory. You should consider the two phases of the disease and how the presence or absence of a "vector" affect the trade-offs between the two phases.

The virulence of parasites is shaped by evolutionary trade-offs at different biological scales. At the host population scale, parasites that are able to best monopolize susceptible individuals tend to be most successful. However, the ability of a parasite to monopolize susceptible hosts is intimately tied to its ability to persist within hosts and to spread effectively between them. Because parasites must ultimately be successful at both the within- and between-host scales, virulence is expected to evolve to balance these potentially conflicting selection pressures. In other words, successful parasites must be able to infect members of a species, but also spread to other hosts. A vector is an organism that carries a disease and can transmit it to other organisms. In order for a parasite to be successful, it must be able to transfer to other individuals so that it does not die along with the host. In terms of trade-offs, for a parasite to successfully monopolize an individual, it needs to take advantage of the individual and then transfer to a new host. However, infections spread through symptoms and these symptoms can be too severe for the host and may kill the host before it can infect others. So, it order to infect others, the symptoms must be benign, however this takes time and the host may die before this takes place. This is why diseases and parasites are not always benign even though selection favors benignness.

By altering habitat and decreasing the number of patches available to a species with metapopulation dynamics, humans increase the risk of extinction for the species. Why? In terms of the simple metapopulation model, what critical thing happens that causes global extinction (i.e. P falls to zero) and why?

There are less empty patches to move to. When dispersers try to colonize a new patch, the new patch may not have been vacant long enough to undergo succession that would keep the patch healthy. When dispersers end up going to the new patch which is not ready, they run out of resources quickly. The continual fight for resources pushes the species to extinction. If P falls to 0, or global extinction, there are no empty patches to be colonized. In other words, global extinction will occur when there is no place for populations to disperse to, so they use up all their resources quickly and die out.

What type of survivorship curve (type I, II, or III) does the species with the following life table have? Explain how you came to your conclusion. x: 0, 1, 2, 3 n_x: 1000, 100, 10, 1

This species have a type II survivorship curve. The population drops by 90% after one year (1000-->100), then another 90% after another (100-->10), and another 90% after another (10-->1). Thus, the survivorship rate has remained the same every year, only ten percent survive every year.

You observe two species with quite different life history patterns. Species A lives a short time, has early maturity, and has many small babies. Species B lives considerably longer, has later maturation, and has far fewer babies. Use these two species to contrast the difference between the old r-and-K selection approach to life history evolution and the more recent optimal demography approach. Thus, explain in general terms how each of the two approaches would account for the differences between Species A and B.

Using the old r-and-K selection approach, Species A, who has a shorter life, early maturity, and many small offspring, is an r-selected species, while Species B, who has a longer life, later maturity, and few large offspring, is a K-selected species. Using the optimal demography approach, the optimal life history is demonstrated by the higher R_0, as trade-offs and mortality patterns must be considered. However, the optimality approach shows us that both life histories are viable and just different ways of looking at things because the high death rate and birth rate in Species A matches the low death rate and low birth rate in Species B. So essentially, r-and-K selection approach looks at traits, and while this works sometimes, most organisms do not cleanly fit into one category. On the other hand, the optimality demography approach offers a mathematical analysis of the life history approaches without restricting them to only two categories.

The optimal demography approach to studying the evolution of life history traits combines demography and natural selection (fitness is equated with population growth rate of different strategies). Show that you understand this approach by comparing the relative fitness of two different life histories --annual versus perennial. Write the fitness equations for each strategy and then determine the fitness of the annual and perennial by putting the specific parameter values indicated below in the equations. Finally, state which strategy would be favored by natural selection and why. B_A (babies per annual female) = 20 B_P (babies per perennial female) = 10 S_0 (survival rate of babies of both types to next year) = 0.1 S (survival rate of adult perennial to next year) = 0.5

We compare lambda for annual and lambda for perennial since approach assumes population growth rate of each strategy (lambda) is a measure of fitness. One with highest fitness (lambda) favored by selection. lambda annual = B_A * S_0 = 20 * 0.1 = 2.0 lambda perennial = B_P * S_0 + S = 10 * 0.1 + 0.5 = 1 = 0.5 = 1.5 lambda annual > lambda perennial so annual is favored by natural selection

What evidence is there that predators affect prey density?

We often observe cycles in predator and prey populations that seem to coincide with one another. For example, as the population of prey increases, so does the population of predators, likely due to the increase in resources increasing their carrying capacity. As more predators enter the population, prey populations decrease, likely due to predation from the increased number of predators. Predator populations will decrease, as their food becomes more scarce and the cycle begins again. Specifically, we have observe between hares and foxes and lynx.

If you surveyed two islands of identical size and distance from the mainland, would you expect to find an identical list of species on the two islands? Why or why not (be sure to use the term that is specifically used to address this issue)?

We would find different species due to "turnover": the equilibrium number of species on an island stays the same but the list of species changes over time due to the balance of random extinction and random immigration of species.

mutation accumulation theory

Weak selection against late-acting genes, so they accumulate.

Species cannot be described as purely mutualistic or purely harmful because the nature of their interactions with other species depends on which species they are interaction with. This point is illustrated by the biology of the honeyguide, particularly a comparison of the breeding biology (what chicks do) and the foraging ecology (how the parents get food). Explain.

While the interactions between humans and honeyguides are mutualistic, honeyguides cannot be described as purely mutualistic due to the nature of their interactions with other species. Honeyguides, like cuckoos and cowbirds, are sometimes brood parasites, and the chicks have a killing hook on their mandibles that they use to kill host chicks. Thus, a honeyguide is not purely mutualistic, nor is it purely harmful. Animals have many different types of interactions with other species and can fall into many categories.

Distinguish between a functional response and a numerical response by predators.

While they are both features that could stabilize prey populations, a functional response is the change in predator's rate of prey consumption with change in prey density and a numerical response is the change in predator density as a function of change in prey density. In other words, a functional response is when a predator adjusts the amount of prey it eats in response with how much prey is available (i.e. not overeating and not undereating so that prey populations are consistent), while a numerical response is when the actual number of predators in the area changes in response to the number of prey in the area (i.e. not creating too many mouths to feed which could harm prey populations).

It is thought that mutualisms can evolve from interactions that start out as purely parasitic relationships. What evidence from yucca moths and their relatives provides support for this idea? Your answers should include a brief description of the biology of yucca moths and their relatives.

Yucca moths have a specialized obligate relationship with plants. The yucca moth engages in active pollination when it lays its eggs. The moth enter the flower and lays 1-5 eggs per flower. It scrapes pollen off its anthers and rolls it into a ball. It then takes the ball to the next plants and places it on the stigma. In pollinating the plant, the plant will sacrifice 10-20% of its seeds to the yucca moth larvae (who feed on the seeds) in return.

Parasite cuckoos in Europe and the songbirds they parasitize provide convincing evidence that co-evolution has shaped traits and behaviors seen in the cuckoos and their hosts. a. What is co-evolution? b. Outline the hypothesized co-evolutionary process that has taken place between cuckoos and their hosts. For each of the two participants--cuckoos verses hosts--indicate specifically which trait or behavior has negatively impacts the other participant and how this has caused natural selection for a response by the harmed party. c. Outline the evidence for each of the proposed steps of the co-evolutionary process.

a. Co-evolution is a reciprocal evolutionary response in two interacting species. In other words, the influence of two closely associating species on each other in their evolution. b. - The cuckoo is a brood parasite - It lays its eggs in the nests of other species ("hosts") and the host raises the chicks. - The cuckoo chicks are much larger than the hosts, requiring more food and more space. - The host, in an attempt to keep all the chicks happy and fed, often loses its own babies to starvation as the cuckoo chick dominates the nest. - So, a co-evolutionary process has evolved between cuckoos and their hosts: - The hosts evolve egg recognition and rejection and, if they recognize a cuckoo egg in their nest, will often destroy the cuckoo egg - This has a negative impact on the cuckoo and this leads to the cuckoo mother evolving egg mimicry and host specialization to lay eggs that mimic different host eggs in response. - The cycle begins again c. An experiment to assess whether host egg rejection favors the evolution of egg mimicry: - Because in nature, current mimicry is so good that there is little egg rejection - Use fake eggs - Mimetic versus non-mimetic and look at rejection rate - Mimetic eggs are rejection 0% of the time - Non-mimetic eggs are rejected 62% of the time - So, yes, host recognition and egg rejections favors the mimetic egg

The Lotka-Volterra competition model enables a graphical approach for determining the ecological outcome of competition between two competing species. Below is a graph that needs to be completed for the following specific case: species 2 impacts the carrying capacity of species 1 (this effect is represented by the parameter a). In contrast, species 1 does not affect the carrying capacity of species 2 (the effect is represented by the parameter B). Despite the competition, both species can coexist. a. Fill in the graph below by adding the following: - the isocline for each species, indicating which one is for species 1 versus species 2 - the equilibrium point - the carrying capacities (K_1 and K_2) on their respective axes b. Are these models density-dependent or density-independent? Explain how you know. c. The Lotka-Volterra competition models explore the ecological outcome of competition. Discuss one evolutionary outcome of competition and describe a pattern or comparison that would support this evolutionary scenario.

a. Species 1 have a straight negative sloping line and species 2 has a horizontal straight line through the center. The equilibrium point is where the two lines intersect. K1 is where species 1 isocline meets the x-axis and K2 is at the species 2 isocline. b. Density dependent because: - models are based on the logistic model, which is density-dependent - or because they are based on K (carrying capacity) which leads to density-dependence c. Character displacement or divergent evolution or niche differentiation. Evidence would be that morphological traits important to competition differ more where the two species co-occur (in sympatry) than where populations of each species do not overlap (in allopatry).

A simple model of the population growth rate (lamda) of an annual versus perennial strategy provides a clear illustration of one approach to studying life history evolution. This approach assumes that natural selection favors the strategy that maximizes fitness (measured by the lambda of the strategy) in the face of extrinsic mortality (and trade-offs, though we ignored them in this simplest case). The parameters of the model for the annual and perennial strategies are: For the annual: - S_0 is the proportion of babies that survive to year 1 to breed - B_A babies are produced per adult - because it is annual, the adult dies after breeding For the perennial: - S_0 is the proportion of babies that survive to year 1 to breed - B_P babies are produced per adult - S_P is the proportion of adults that survive each year With this information: a. Show the equations for lambda for the annual and perennial strategies. b. Use these two equations to show the conditions under which being an annual is a better life history strategy than being a perennial (i.e. lambda annual > lambda perennial). c. Rearrange the equations to show that the life history trade-offs between annual and perennial reproduction entails two things: (i) the differences between the two strategies in the number of babies produced and (ii) the survival of adults relative to babies.

a. lambda_A = S_0 * B_A where lambda_A represents the growth rate of an annual population lambda_P = (S_0 * B_P) + S_P where lambda_P represents the growth rate of a perennial population b. When is annual favored over perennial? - When lambda_A > lambda_P or when B_A * S_0 > (B_P * S_0) + S_P - In other words, lambda_A is favored over lambda_P when the the number of annual babies that survive to year 1 to breed is greater than the number of perennial babies that survive to year 1 plus the adults that survived. c. - B_A * S_0 > (B_P * S_0) + S_P - Divide by S_0 to get B_A > B_P + (S_P/S_0) - Subtract B_P to get B_A - B_P > S_P/S_0

The Lotka-Volterra predation models examine the population dynamics of a specialist predator that feeds on a single species of prey. The change in prey numbers per unit time is given by the following equation: dV/dt = rV - aVP where: V = prey numbers P = predator numbers r = per capita growth rate of prey without predation a = kill efficiency (number of predator prey encounters where prey is killed) Show that you understand what is meant by doing the following: i. Convert the above equation to the equation for the prey isocline. Make sure that the final equation is arranged so that the X and/or Y variables are correctly identified so that the equation can be graphed with the X and Y axes shown below. Show all statements and steps required to indicate an understanding of the term "isocline." ii. Plot the isocline on the graph below and label the value of the axis where the line intercepts it. iii. Use arrows to indicate the direction of prey population change on each side of the prey isocline on the graph.

i. Isocline is equation for all densities of predator and prey for which prey population is stable. i.e. for which dV/dt = 0, which occurs when: rV = aVP r = aP r/a = P P = r/a this is the isocline equation ii. A straight horizontal line in the center. Value is r/a iii. Above line points to right, below line points to left.

Timing to maturity (i.e. age at first reproduction) is an important life history variable that varies enormously among species. According to life history theory, adaptive timing of maturity entails a trade-off between beginning reproduction too early and too late--waiting to begin breeding thus has costs and benefits. (i). Name one general cost (or risk: think life table) and one benefit to delaying maturity. (ii). What comparative pattern among species suggests that differences in either the cost or benefit affect the evolution of optimal timing of maturity? (iii). What experiment would one conduct to show that natural selection can change the timing of maturity (refer to the guppy paper or design your own experiment)?

i. One cost could be mortality. The longer you wait, the lower the chance of you being alive when it comes time to reproduce. One benefit could be waiting would allow you to continue growing. If you continue growing, you have a larger body size, which has proven to be a reproductive advantage (i.e. larger females produce more eggs and larger males can attract more mates). ii. A pattern that suggests that differences in either cost or benefit affect the evolution of optimal timing of maturity is that we observe variation in survival rates that correlate with age of maturity. We observe that organisms that experience a higher annual survival tend to mature later on. iii. One could conduct an experiment such as the long-term study of guppies in which the predictions of life history theory are supported: Life history differences among populations of guppies are closely associated with predator species with which guppies live. The predators apparently alter age-specific survival because they are size-specific in their choice of prey. A cichlid, the main predator at one class of localities, preys predominantly on large, sexually mature size classes of guppies. A killifish, the main predator at another class of localities, preys predominantly on small, immature size classes. Guppies from localities with cichlids mature at an earlier age, have higher reproductive effort, and have more and smaller offspring per brood than those from localities with theoretical predictions. To prove that predation of guppies caused this pattern, one can perturb a natural population of guppies by changing predation against adults to predation against juveniles and observe for 30-60 generations to see if guppies will now mature later.

Explain fully, in words, the basis of the Lotka-Volterra competition models (i.e. the basic recipe as outlined in class). Point out what simple population model serves as the starting point and what modifications are added to examine the population consequences of two competing species. How does one go from the models to isoclines and how do these isoclines tell us about the outcome of competition? What possible GENERAL outcomes are predicted by this model?

i. Two species, each have their own logistic population model dN/dt = rN(1-N/K). ii. The two species compete (i.e. consume shared resources; hog part of each other's K). iii. Competition coefficients indicate the impact of the species on each other and allow us to convert numbers of one species to numbers of the other. iv. Therefore, the carrying capacity (K) of each species is reached by mixture of individuals of both species; the isocline for a species is the equation (and line on a graph) that represents all possible combinations of densities of the two species for which the population of the focal species is stable (i.e. dN/dt = 0). v. We plot both isoclines on state space graph [population size of species 1 (N_1) on the x-axis, of species 2 (N_2) on the y-axis]. vi. We visually inspect the regions of the graph and look at the joint movement of both populations in each area to assess the outcome of competition. vii. The two general outcomes are stable coexistence or competitive exclusion.

The magnitude of the competition coefficients used in the Lotka-Volterra competition models tells us about the relative strength of two types of competition: intraspecific and interspecific competition. a is the effect of species 2 on species 1, B is the effect of species 1 on species 2. Describe the relative strength of intraspecific versus interspecific competition when: i. a = 1 ii. B > 1 iii. a < 1 iv. B = 0 v. What does is mean is a > B?

i. When a = 1, the effect of species 2 on species 1 is equal to the effect species 1 has on members of its own species. In other words, interspecific competition is equal in strength to intraspecific competition in this case. ii. When B > 1, the effect of species 1 on species 2 is greater than the effect species 2 has on members of its own species. In other words, interspecific competition is stronger in this case than intraspecific competition is. iii. When a < 1, the effect of species 2 on species 1 is less than the effect species 1 has on members of its own species. In other words, intraspecific competition is stronger in this case than interspecific competition is. iv. When B = 0, then there is no effect of species 1 on species 2, so there is no interspecific competition. v. When a > B, that means that the effect of species 2 on species 1 is greater than the effect of species 1 on species 2. in other words, species 2 is outcompeting species 1 and species 1 will go extinct.

The equilibrium theory of island biogeography was developed to explain two interesting relationships: a. the relation between diversity (number of species) and area and b. the difference in patterns of diversity between mainland areas and islands (and how far an island is from a mainland source). Fill in the graph below to illustrate how the Theory of Island Biogeography can explain why bigger islands have more species than smaller islands. Label the x-axis and all of your immigration and extinction lines and be sure to indicate the equilibrium numbers of species on each of the two islands.

x-axis: # species (S) y-axis: rate of gain or loss of species Immigration line should be a straight negative sloping line. Extinction lines of the small island and large island should both we straight positive sloping lines, but the small island line should be steeper (thus above) the large island line. The equilibrium numbers are wherever two lines intersect. The equilibrium point of the small extinction line should be labeled S_small and the equilibrium point of the large extinction line should be labeled S_large.