Ecology Exam 2

Graphical solutions for Lotka-Volterra predation presented in Figure 12.14.

(Read highlighted blue section on study guide Chapter 12)

induced defenses in plants

(stimulated by herbivore attack), as illustrated by individual cacti that increase their production of spines only after they have been grazed

Lotka-Volterra predator-prey model

- N-# of prey individuals - P - # of predator individuals (Read highlighted yellow section on study guide Chapter 12)

what role do fungal endophytes play in communities?

- Spend whole life here - Some are mutualistic and some don't do anything at all

Parasitoids

- insects that typically lay one or a few eggs on or in another insect (the host) - After they hatch from their eggs, the parasitoid larvae remain with the host, which they eat and usually kill -can be considered unusual parasites (because they consume most or all of their host, almost always killing it) or unusual carnivores (because over the course of their lives they eat only one individual, killing it slowly)

Batesian mimicry

-A harmless species imitates the warning signals of a harmful species -example: western coral snake vs. Mexican milk snake -example: Scarlet king snake vs. mountain king snake -the exhibition of the characteristics of a dangerous species by a harmless species to avoid predators

Avoidance in respect to plants and herbivory

-A reaction to conflict that involves ignoring the problem by doing nothing at all, or deemphasizing the disagreement. -This is known as masting- allows plants to hide (in time) from seed-eating herbivores, then overwhelm them by sheer numbers -Plants can also avoid herbivores in other ways, such as by producing leaves at times of the year when herbivores are scarce

· What are Beltian bodies, and how are they involved in insect-plant interactions?

-Beltian bodies are modified leaflet tips that are high in protein and fat - Plant secretes nectar from these and ants feed on them - The ant lays eggs inside acacia's thorns and will aggressively attack insect and even mammalian herbivores that attempt to eat the plant - The ants also maul other plants that are within 10-150 cm of their home acacia- they provide the acacia with a competitor-free zone in which to grow

Lotka-Volterra competition model

-Competition deprives species of resources and hence reduces population growth rates. -To incorporate the effects of the competitor species on one another, we can modify the logistic equation of each species by subtracting a competition coefficient, which is a constant used to indicate how strong the competitive effect of one species is on another. (Look at highlighted green section in study guide 14)

· Why might positive interactions be more common in stressful environments?

-Positive interactions may be more common in stressful environments o Positive interactions found at higher latitudes o Researchers found positive interactions at high elevation sites o Negative interactions at low elevation sites o Positive interactions more common in colder, more stressful environments and competition was more common in warmer, less stressful environments and intertidal communities - The strengths of one species may make up for weakness in another species; in harsher conditions, the weaknesses are much more prevalent and influential when it comes to survival, so positive interactions help reduce the negative effects that a species' weaknesses have on its survival.

What are some ecological consequences of mutualisms that can extend beyond the interacting pair of organisms?

-Providing species with favorable habitat can increase distribution o Ex: coral providing algae with a habitat, fungi allowing plants to live where they otherwise wouldn't, forests allowing animal and plants to survive because of lower competition - Mutualisms can increase community diversity o Ex: cleaner fish remove parasites from larger fish, allowing more species to survive and increase community diversity and abundance

· Explain how both competition and physical factors affect the distribution of intertidal barnacles in the example given in the book.

Semibalanus barnacles are excluded from the top of the intertidal zone by its sensitivity to desiccation, and Chthamalus barnacles are excluded from the lower portions of the intertidal zone due to competition for space with the Semibalanus.

type III functional response

Similar to II, slow increase, followed by dramatic increase which then levels off. This is due to saturation occurring at high density levels.

What might be an example of character displacement? a. Two species of closely related birds have divergent (or different) beak sizes when they are found in the same location. b. A species is excluded (displaced) from its native range as a result of interaction with a superior competitor. c. Multiple species evolve a similar resource-extraction phenotype (e.g. beak size) in response to similar environmental conditions. d. Two species of closely related birds have similar beak sizes when living in isolation. e. None of the above.

a.

Commensalism

an interaction in which individuals of one species benefit, while those of the other species do not benefit and are not harmed (+/0) relationship)

Consider the Lotka-Volterra state space shown. What is the arrow pointing to? (Look at image on Quiz 4 question 5) a. a modification to account for prey carrying capacity. b. the predator isocline. c. a modification of base theory to simulate metapopulation dynamics. d. the prey isocline. e. none of the above.

b.

The image shows an arrangement of isoclines representing one possibility for Lotka-Volterra competition. The white dot indicates the starting conditions. What outcome does this arrangement predict? (Question 3 on quiz look at graph) a. The second species (N2) will win, N1 goes extinct. b. Coexistence (both species persist at some intermediate density). c. The first species (N1) will win, N2 goes extinct. d. Both species driven to low densities and/or extinction. e. All of the above are possible (not knowable based on the illustrated starting conditions).

b.

What caused the downfall of the American chestnut in eastern forests? a. over-harvest by the timber industry. b. an introduced fungal pathogen. c. competition from exotic and invasive plants. d. tourism. e. all of the above.

b.

Which of the following would be an example of Batesian mimicry? a. A spider mimics moth pheromones to lure prey. b. A moth mimics spider behavior to avoid predation. c. The color pattern of a venomous snake is imitated by other snakes in the same area. d. A number of venomous snakes have converged on the same color pattern. e. A number of toxic plants have converged on a successful toxin that deters herbivores.

c.

Intraspecific

competition between the same species

Interspecific

competition between two different species due to limited resources

Habitat mutualism

one partner provides the other with shelter, a place to live, or favorable habitat o Ex: pistol shrimps form a habitat mutualism with some gobies in environments with abundant food but little protective cover § Shrimp digs burrow that it shares with goby- provides the fish with a safe habitat from danger § Goby serves as seeing-eye fish for the shrimp, which is blind

mycorrhizae

symbiotic associations between plant roots and various types of fungi that are mutualistic

What does it mean to say that the "net benefits must outweigh the net costs" for both partners in a mutualism?

-For an ecological interaction to be a mutualism, the net benefits must exceed the net costs for both partners. However, neither partner in a mutualism is in it for altruistic reasons. - Should environmental conditions change so as to reduce the benefits or increase the costs for one of the partners, the outcome of the interaction may change. o especially true if the interaction is not obligate. o Ants, for example, often form facultative relationships in which they protect other insects from competitors, predators, and parasites. In one such case, ants protect treehoppers from predators, and the treehoppers secrete honeydew (a sugar syrup substance), which the ants feed on o Treehoppers always secrete honeydew, so the ants always have access to this food source. o However, in years when predator abundances are low, the treehoppers may receive no benefit from the ants. In such years, the outcome of the interaction may shift from +/+ (a mutualism) to either +/0 (a commensalism) or +/- (parasitism), depending on whether the consumption of honeydew by ants reduces treehopper growth or reproduction.

· Describe the "nurse plant" phenomenon.

-In desert environments, the soil beneath an adult plant is often cooler and moister than the soil of an adjacent open area. - differences may be so pronounced that the seeds of many plant species can germinate and survive only in the shade provided by an adult plant; such adults are called nurse plants because they "nurse" or protect the seedlings. - A single species of nurse plant may protect the seedlings of many different species. o Ex: Desert ironwood serves as a nurse plant for 165 different species, most of which can also germinate and grow under other plant species. o This situation is typical of facultative interactions: a species that requires "nursing" may be found under a variety of nurse plant species (and hence has a facultative relationship with each of them), and the nurse plant and the beneficiary species may evolve little in response to one another.

Explain an example in which changing climatic conditions affect the spread of a disease.

-Increases in ocean temperature strongly correlate with increases in coral diseases along the Great Barrier Reef. (Bruno et al. 2007) -The number of people at risk from malaria, cholera, and the plague may increase as global temperatures continue to warm. (Ostfeld 2009)

What does it mean to say that competition is "asymmetrical"?

-It is meant that one population is so good at getting resources (rodents) that when they're removed, the smaller population (ants) thrive, but if the ants are removed, the rodents aren't affected or don't care. -When two species compete for a resource that is in short supply; one species usually gets less of the resource than it could have if the competitor were not present. Competition reduces resources available for growth, reproduction, survival of both species

Describe the natural history of the fig / fig wasp mutualism.

-Many tropical fig trees are pollinated by one or a few species of fig wasps. - Relationship is mutually beneficial and obligate for both species in that neither species can reproduce without the other. - Show clear signs of coevolution - Fig flowers are contained within structures of fleshy stem tissue known as receptacles In monoecious figs (those in which each tree has separate male and female flowers), the male and female flowers are located in different parts of the receptacle, and the male flowers mature after the female flowers. The forms of female flowers range from those with short styles to those with long styles. - A female fig wasp enters the receptacle, carrying pollen she collected from male flowers in another receptacle. Once inside, the wasp inserts her ovipositor through the styles of the female flowers to lay eggs in the ovaries (see Figure 15.6). She then deposits pollen on the stigmas of those flowers. The wasp pollinates both long-styled and short-styled flowers, and hence both flower types develop seeds. Perhaps because wasp ovipositors are not long enough to reach the ovaries of long-styled flowers, wasp larvae typically develop within short-styled flowers and feed on some of their seeds. - When the young wasps complete their development, they mate, the males burrow through the receptacle, and the females exit through the passageway the males have made. Before the females leave the receptacle, however, they visit male flowers (which are now mature), collect pollen from them, and store it in a specialized sac for use when they lay their eggs in another receptacle. The wasp's reproductive behavior is a remarkable example of a specialization that provides a benefit to another species.

What's the difference between obligate and facultative interactions? and give an example of each.

-Mutualism and commensalism range from those that are obligate (that is, required for species) to those that are facultative (not required). - Obligate examples: o The leaf-cutter ant-fungus mutualism: the ants and the fungi they cultivate have a highly specific, obligate relationship in which neither partner can survive without the other, and their interaction has led each partner to evolve unique features that benefit the other species. o Fig/fig wasp mutualism - Facultative examples: o large herbivores such as deer or moose may inadvertently eat the seeds of small herbaceous plants whose leaves they feed on. The seeds may pass unharmed through the herbivore's digestive tract and be deposited with its feces, often far from the parent plant o dispersal of offspring away from parents may be advantageous, so benefits may accrue to both the plant (whose seeds are dispersed) and the herbivore (which feeds primarily on leaves).

what role did mycorrhizae play in communities?

-Mycorrhizae provide clear benefits to the plants, improving their growth and survival in a wide range of habitats - One way mycorrhizal fungi benefit plants is by increasing the surface area over which the plants can extract water and nutrients from the soil - may also protect the plants from pathogens, while the plants typically benefit the fungi by supplying them with carbohydrates. - The name for the association between underground fungi and plant roots - Fungi make the plant roots more effective - Plant gives fungus a place to stay and some resources

What is meant by a conditional mutualism?

-Positive interactions can cease to beneficial under some circumstances - Depending on the circumstances, an interaction between two species may have either positive or negative outcomes -Ex: soil temp influences whether a pair of wetland plant species interact as commensals or competitors -Positive interactions may be more common in stressful environments -Positive interactions found at higher latitudes -Researchers found positive interactions at high elevation sites -Negative interactions at low elevation sites -Positive interactions more common in colder, more stressful environments and competition was more common in warmer, less stressful environments and intertidal communities -Mutualism can shift from being plus plus to something else given some type of variation (like in environment or time changes) The mutualism is conditional upon environment

What prevents mutualistic interactions from being broken down by "cheaters"? and understand the relevant example from yuccas and their pollinators.

-There is an inherent conflict of interest between the partners in mutualism: the benefit to each species comes at a cost to the other. - In such a situation, natural selection may favor cheaters,- individuals that increase their production of offspring by overexploiting their mutualistic partner. - When one of the partners in a mutualism over exploits the other, it becomes less likely that the mutualism will persist. But mutualisms do persist - 1) "penalties" imposed on individuals that overexploit a partner can reduce or remove any advantage gained by cheating o obligate, coevolved mutualism between the yucca plant and its exclusive pollinator, the yucca moth o Female yucca moths collect pollen from yucca plants with their unique mouthparts o After collecting pollen, a female moth typically moves to another plant, lays eggs in the ovary of a flower, and then walks up to the top of the style. There, the moth deliberately places some of the pollen she carries on the stigma, thus pollinating the plant o The larvae that hatch from the moth's eggs complete their development by eating some of the seeds, which then develop in the ovary of the flower. o The moth and the plant depend absolutely on each other for reproduction. However, the mutualism is vulnerable to overexploitation by moths that lay too many eggs and hence consume too many seeds. o **Yuccas have a mechanism to prevent such overexploitation: they selectively abort flowers in which female moths have laid too many eggs (they abort before moth larvae hatch from their eggs)**

symbiosis

-a relationship in which individual's of the two species live in close physical and/or physiological contact with each other -example: relationships between pea aphids and their bacterial symbionts; between humans and bacteria (we have a diverse set of bacteria living in our guts, many of which are beneficial -symbiotic c relationships can range from parasitism (+/-) to commensalism (+/-) to mutualism (+/+)

secondary compounds in plants

-also produce a wide variety of chemicals, that function to reduce herbivory. -some are toxic, protecting the plant from all but the relatively small number of herbivore species that can tolerate them. -Others serve as chemical cues that attract predators or parasitoids to the plant, where they attack herbivore -Some plant species, such as oak trees, produce these compounds constantly, regardless of whether herbivores have attacked the plant. -In other species, the production of these compounds is an induced defense. -Example: when attacked by herbivores, a North American tobacco species, Nicotiana attenuata, produces two induced defenses: toxic secondary compounds that deter herbivores directly, and volatile compounds that deter herbivores indirectly by attracting predators and parasitoids.

An example of a trade-off associated with defense against predation

-among four species of marine snails eaten by the green crab, the species whose shells could be crushed most rapidly by crabs were the quickest to take refuge when crabs were detected, and vice versa -The exact negative correlation between resistance to crushing and predator avoidance behavior suggests that there may be a trade-off between a snail's physical and behavioral defenses.

Defense in respect to plants and herbivory

-enormous array of structural and chemical defenses to ward off herbivores -the leaves of many plants are tough, and many plant bodies are covered with spines, thorns, sawlike edges, or pernicious (nearly invisible) hairs that can pierce the skin like miniature porcupine quills

Compensation in respect to plants and herbivory

-occurs when removal of plant tissues stimulates a plant to produce new tissues, allowing for relatively rapid replacement of the material eaten by herbivores -When full compensation occurs, herbivory causes no net loss of plant tissue -may occur when removal of leaf tissue decreases self-shading, resulting in increases plant growth, or when removal of apical buds (those at the end of a branch or shoot) allows lower buds to open and grow -if the amount of material removed from a field gentian-or any other plant-is large enough, however, or if insufficient resources are available for growth, the plant cannot fully compensate for the damage.

Mullerian mimicry

-two or more harmful species mimic each other's warning signals -is the exhibition of similar characteristics by similar species to avoid predators -example: The black and orange spider is found in the same habitat as the velvet ant and can mimic each others warning signals

Why is the parasitic lifestyle so extremely common?

1. Living on or in your primary food resources comes with some obvious advantages. 2. The parasitic lifestyle apparently facilitates specialization which we can expect to be associated with ecological success. 3. Close ecological association facilitates speciation.

Parasite

An organism that lives in or on a host organism and feeds on its tissues or body fluids.

Allelopathy

A mechanism of competition in which individuals of one species release chemicals that harm individuals of other species

Competition

A non-trophic interaction in which individuals of the same species (intraspecific) or different species (interspecific) are harmed by their shared use of a resource that limits their ability to grow, reproduce, or survive (-/- relationship).

Endoparasite

A parasite that lives inside the body of its host organism.

Ectoparasite

A parasite that lives on the surface of another organism.

character displacement

A process in which competition causes the phenotypes of competing species to evolve to become more different over time, thereby easing competition.

What are some "costs" associated with host defense and parasite counter defense?

A trait that improves a host's defenses or a parasite's counter defenses may have costs that reduce other aspects of the organism's growth, survival, or reproduction.

Paradox of enrichment

As prey populations increase dramatically, predator populations will follow suit. Once at high densities the predator population may crash, leading to local eradication or even extinction.

What are some of the advantages and disadvantages of both endo- and ectoparasitism?

Advantages of Endoparasitism= Ease of feeding, protected from external environment, safer from enemies Advantages of Ectoparasitism= Ease of dispersal, safe from host's immune system Disadvantages of Endoparasitism= Vulnerability to host's immune system, dispersal difficult Disadvantages of Ectoparasitism= Vulnerability to natural enemies, exposure to external environment, feeding more difficult

Resource availability

Allocation of resources to anti-herbivore defenses differs between species according to their growth rates. Fast-growing species in resource-rich environments suffer a high cost of diverting energy from photosynthetic tissue, but a low cost of losing tissue, so are less well defended.

Interference competition

An interaction in which species compete directly by performing antagonistic actions that interfere with the ability of their competitors to use a resource that both require, such as food or space.

exploitation competition

An interaction in which species compete indirectly through their mutual effects on the availability of a shared resource.

Host

An organism on or within which an herbivore, parasite, or mutualist lives and feeds.

How can disturbance promote coexistence?

By altering the strength and direction of consumer resource interactions. o A natural reset o A major storm may kill or damage some individuals while also creating opportunity for others. o Forests contain herbaceous plants (primrose) that require abundant sunlight and is found in areas where wind or fire create an opening in the canopy

3 broad categories of predation

Carnivory: The predator (a carnivore) and prey are both animals Herbivory: The predator (a herbivore) is an animal and the prey is a plant or alga Parasitism: The predator (a parasite) lives in symbiosis (close physical and/or physiological contact) with its prey (a host) and consumes certain tissues without necessarily killing the host - Some parasites are pathogens that cause disease in their hosts

Describe three hypotheses to explain diet specialization.

Competition: specializing in one type of prey reduces competition with other species - Can evolve to better utilize this resource Variation in Resources: a more predictable climate lends itself to a narrower diet breadth. -Species in climates with little resources are more likely to be generalists. Predator Avoidance: Diet specialization more likely if it evolves as part of crypsis/defense (trade off between predator avoidance and resource utilization)

What is meant by the "coevolution" of parasites and hosts? Understand the example of European rabbits introduced to Australia to illustrate your answer.

Host and parasite populations can evolve together, each in response to selection pressure imposed by the other. The European rabbits developed increased resistance to the virus, and the virus evolved to become less lethal.

What is meant by the idea that predation and herbivory can cause a "shift" from one community type to another?

If predation persists on particular prey types, the prey can become dispersed or removed from the community which alters it to a different community type.

Screening Hypothesis

Phytochemical diversity isitselfan anti-herbivory mechanism whereby plants produce a range of compounds, with the result that some compound or combination can be effective for a particular herbivore.

What have we learned from snowshoe hares about predation and the factors that affect prey dynamics?

Predation and food supply both impact hare population cycles, less predators or more food increases populations alone, and exponentially increases populations when combined.

Explain what Huffaker's classic experiment (in Figures 12.15 and 12.16) demonstrates about predator-prey dynamics.

Predators and prey coexist with one another with constant fluctuations in density. Both populations are susceptible to extinction when an unnatural predator is introduced.

Plant Apparency Hypothesis

The most easily found plants are the most likely to be collected and used by other species. Long-lived species invest in quantitative defenses, while ephemeral species escape in time and invest in qualitative defenses.

What caused the downfall of the American chestnut (Castanea dentata)?

The parasitic fungus Cryphonectria parasitica that causes chestnut blight, a disease the kills chestnut trees.

competitive exclusion principle

The principle that two species that use a limiting resource in the same way cannot coexist indefinitely.

Understand equation 13.1, and understand what is meant by a "threshold density" in host-pathogen population dynamics.

The threshold density is the minimum number of individuals susceptible to a disease that must be present in a population for the disease to become established and spread. (Look at Equation on study guide chapter 13, highlighted purple)

resource partitioning

The use of limiting resources by different species in a community in different ways.

How the incorporation of a victim carrying capacity modifies the Lotka-Volterra predation model. Also, how the incorporation of a predator functional response modifies the model.

When a carrying capacity is implemented the fluctuations of the predation model change significantly. As there is now a capacity to the prey, there is also a capacity to the predators. As prey decreases due to predation, predators will starve and die off and when their population levels drop, prey levels increase again.

Predation

a trophic interaction in which an individual of one species, a predator, consumes individuals (or parts of individuals of another species, its prey

Consider the Lotka-Volterra state space shown. If the white dot is the current condition, what should be happening? (Look at image on Quiz 4 question 2) a. both prey and predator densities should be increasing. b. prey density should be decreasing, while predator density should be increasing. c. prey density should be increasing, while predator density should be decreasing. d. both prey and predator densities should be decreasing. e. the system is at equilibrium (neither predator nor prey densities should be changing).

a.

The image shows an arrangement of isoclines representing one possibility for Lotka-Volterra competition. The white dot indicates the starting conditions. What outcome does this arrangement predict? (Question 4 on quiz look at graph) a. The second species (N2) will win, N1 goes extinct. b. Coexistence (both species persist at some intermediate density). c. The first species (N1) will win, N2 goes extinct. d. Both species driven to low densities and/or extinction. e. All of the above are possible (not knowable based on the illustrated starting conditions).

a.

Trophic mutualism

a mutualism in which one or both of the mutualists receives energy or nutrients from its partner o Ex: leaf-cutter ant-fungus mutualism § Each partner feeds the other (Recall that the ant and the fungus also help each other to overcome plant defenses, so each also provides the other with an ecological service.)

mutualism

a mutually beneficial interaction between individuals of two or more species (+/+ relationship)

In the example of the intertidal barnacles (from the book and discussed in lecture), there is one species (call it A) that typically lives lower in the surf, while a second species (call it B) tends to live higher up along the shore. If species A is removed, species B is able to live across the upper and lower intertidal range. If species B is removed, species A does not expand up to the highest intertidal zone. What does this suggest about the two species? a. Competition in these species is symmetrical (i.e. the effect of species A on species B is roughly equal to the effect of B on A); that symmetry is why these species are a classic textbook example. b. The fundamental niche of species A is larger (encompassing a wider range of environmental conditions) than the fundamental niche of species B. c. Competition in these species is less important than environmental factors (e.g. desiccation) in determining distribution and abundance. d. The fundamental niche of species B is larger (encompassing a wider range of environmental conditions) than the fundamental niche of species A. e. Neither of these species can withstand the desiccating conditions of the high intertidal.

d.

Which of the following might be described as a typical parasite? a. A small plant that lives on the trunk of a much larger plant, such as an orchid hanging off the side of a tree. b. Your classmate who never prepares for quizzes and tries to look at your work. c. An animal that feeds off of a large number of host individuals, killing each host before it moves on to another one. d. An animal that spends its entire life feeding off the body of one individual of another, larger species. e. None of the above.

d.

What is allelopathy? a. A mechanism of competition explaining high diversity of coexisting plants, for example in tropical forests. b. The phenomenon in which the realized niche is less than 1/2 the size of the fundamental niche. c. Parallel evolution of competitive ability (for example in closely related species). d. Evolutionary response to allee effects (for example maintaining positive population growth rates even at low density). e. The phenomenon by which one organism produces chemicals released into the environment that have a negative effect on another organism.

e.

type I functional response

exponential linear increase of prey consumed as prey population increases. This model is used in the Lotka-Volterra model.

fungal endophytes

fungi living entirely inside plant (mostly stems and leaves but can be in roots too)

type II functional response

general increase which levels off as prey population increases. Assumption that predators are limited by the capacity to process food.