BIS 2B STUDY GUIDE 19-28

Explain why application of the biological species concept is difficult or impossible in each of the following situations: (a) examples of natural hybridization, (b) the existence of strictly asexual organisms, and (c) disjunct (allopatric) distributions of species.

(a) examples of natural hybridization: grey wolves mating with coyotes=red wolves - rare but can still reproduce naturally (b) the existence of strictly asexual organisms. No reproduction/mating involved, just division (c) disjunct (allopatric) distributions of species - the species live geographically far away/separated by barrier and do not exchange genes freely in nature

Why do most evolutionary biologists agree that allopatric speciation is common but sympatric speciation is not? Focus your discussion on the fundamental difference between these two alternatives, and why that difference is likely to be important for divergence and the evolution of reproductive isolation.

-Allopatric speciation:there is a physical barrier that subdivides a species range into 2 or more populations that species can no longer freely exchange genes. It is much more common because there are clear extrinsic barriers to gene flow. Things like geographical or spatial barriers make gene flow restricted, and thus is more common to see populations diverge. Events that divide a species range are called VICARIANT events.Once vicariance has occurred, the separated populations can independently accumulate genetic differences either through (1) diversifying selection or (2) genetic drift (or both). Since there is a physical barrier, there is not going to be any selection to avoid mating because there is no opportunity to mate with other species. -In sympatric speciation however it is more subtle, and there needs to be microhabitats within the overlapping habitat. There is no obvious geographic barrier to gene flow. For there to be divergence, there would have to be essentially no gene flow between microhabitats.This could happen if a species had very little dispersal potential, or a species exhibited very strong preferences to mate with like phenotypes(positive assortative mating).In sympatric speciation, species have overlapping ranges (so it is possible for them to interact and therefore exchange genes). Sympatry should promote gene flow since there is overlap. Have the opportunity to mate with others and selection should favor the evolution of prezygotic isolation mechanisms. Sympatric species have much higher levels of prezygotic isolation than allopatric. This suggests that Reinforcement when populations become sympatric, shifts from POSTzygotic to PREzygotic.

The semelparous fish species, Oncorhynchus bistwobe, is a new major target of fishing. Most of these fish mature at five years of age and produce on average 1000eggs when they spawn. Some individuals, however, mature at four years of age and produce on average 500 eggs when they spawn. If individuals are only harvested between ages 4 and 5, what level of harvest mortality will result in natural selection favoring the earlier-‐‐spawning individuals? Assume in the absence of fishing, all individuals of age 4 survive to age 5.

50/100 = x/1000, which is x=500 .One could also set the number of individuals. For example, ages 4 is 10 and age 5 is 5, due to half dying during harvesting. So, For age 5: ½(10) x 1000 = 5000 reproduced For age 4: 10 x 500 = 5000 reproduced. So a greater than 50% mortality rate will favor earlier spawning indv.

. What is the biological species concept, and what are its main criteria for defining a species?

A species consists of groups of actually, or potentially, interbreeding natural populations of organisms that are reproductively isolated from other such groups. Species are breeding units that are evolutionarily independent from other breeding units. 1)Individuals do NOT evolve (their genetic composition barring mutation doesn't change). 2) Populations and species DO evolve. 3)Species represent separate evolutionary units that can no longer exchange genes, hence evolve independently of each other. Two individuals are members of DIFFERENT species if they DO NOT produce viable AND fertile offspring in the wild. They DO NOT freely exchange genes in nature

Explain how each of the following factors affect local species diversity. Provide an example to illustrate your answer.A. Environmental variabilityB. Foundation speciesC. Productivity (resource availability)D. Habitat complexityE. CompetitionF. Keystone predatorsG. Disturbance

A. Environmental variability: A fluctuating environment over time can promote diversity. Temporal fluctuation prevents competitive exclusion by altering competitive hierarchy. Example: plankton and algae species coexist because conditions rarely favor one species long enough to exclude others. B. Foundation species: have a large effect on community composition because of their size/abundance, example: kelp forest/trees -increases diversity - creates habitat that allows other species to live there. C. Resource Availability: Adding nutrients typically decreases diversity. Paradox of Enrichment: Increased nutrients leads to higher productivity and biomass, but decreased diversity and increased dominance. example: Rothamsted, England. Adding different types of resources might favor diversity though. D. Habitat Complexity: example:Niche partitioning. A more complex habitat could potentially house more animals.increases diversity by allowing resource partitioning by habitat type. habitat alteration (loss and fragmentation) decreases diversity. More diverse systems are more productive. More diverse systems are better able to withstand environmental variability. And prevent invasion. E. Competition: generally reduces diversity by removing inferior competitors F. Keystone predators: increases diversity by allowing inferior competitors to coexist with prey items that are competitively dominant (remove competitive dominant). Prevents competitive exclusion. Example: Otter's eat sea urchins, controlling their population. If the otters didn't eat the urchins, the urchins would eat up the habitat's kelp. Kelp, is a major source of food and shelter for the ecosystem. G. Disturbance: Community composition can be reset with disturbance. Low diversity with low disturbance AND high disturbance. Highest diversity with mediated disturbance and coexistence. The Intermediate Disturbance Hypothesis (IDH) justifies that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At high levels of disturbance, all species are at risk of going extinct. At intermediate levels of disturbance, diversity is maximized because species that thrive at both early and late successional stages can coexist. Disturbances act to disrupt stable ecosystems and clear species' habitat. As a result, disturbances lead to species movement into the newly cleared area. Once an area is cleared there is a progressive increase in species richness and competition takes place again. Once disturbance is removed, species richness decreases as competitive exclusion increases.

Why have island archipelagoes played such an important role in the development of the science of speciation? What lessons have we learned from studies of speciation in places like the Hawaiian Islands?

Archipelagos are so convenient for studying speciation because they define very clear reproductive (spatial) barriers. We can see that when members of a species happen to disperse from one archipelago to another, after generations of living in allopatry, it is likely that the two groups will diverge enough to become separate species. -Hawaiian Islands-(1)Founder effects/genetic drift + (2) diversifying selection (slightly different habitats on different kipukas) are important for the evolution of new species within an island (hawaiian flies). Essentially, a few "lucky" dispersing propagules cross a geographic barrier, and successfully colonize a new habitat. Most of the reproductive isolation evolves while the populations are allopatric, so that if the populations come back into sympatry, they are substantially isolated. In other words, "SPECIATION IS A BY-PRODUCT OF THE DIVERGENT SELECTION THAT OCCURRED DURING ALLOPATRY" Founder effect/peripatric speciation may be driven by genetic drift(especially in small, newly founded populations), along with diversifying selection. The phylogeny of Hawaiian Drosophila mirrors the order of appearance of the islands. The branching order of the different species on the phylogeny is congruent with the age of emergence of the different islands.

As a result of road building, a formerly contiguous patch of tropical rain forest is now subdivided into smaller patches. The charismatic 8-‐‐striped purple newt lives in the forest, where it has long been among the most abundant species. The newt moves slowly and so cannot cross extensive areas of open ground that lack forest cover (e.g., a road) because it will dry out and die. Conservation groups are interested in understanding the effect of all this road building on the newt, and have enlisted your services as a biological consultant. In your report, you should be able to provide short, well-‐‐justified answers to what you think the effects of road building will be on the ecology and evolution of the newt. For example, how will building roads affect: the risk of newt extinction, recolonization of patches after disturbance, gene flow among newt populations, potential for local adaptation, species richness within a patch, spread of disease, etc. Can you propose an engineering solution that might help avoid these impacts, yet still allow the roads to be built?

Building roads through the newt's habitat will divide it into smaller patches and cut it off from resources. (edge effect) Because the newt moves slowly and will dry out and die in direct sunlight, it needs its habitat to be fully enclosed forest, not the edge forest. Roads will cut off the newt's gene flow from habitat to habitat because it cannot cross from one to the other. It will also disallow recolonization in newly created patches after disturbance. Founder effect will happen in the small leftover patches in between roads and risk of extinction due to shrinking covered forest is great. A solution would be to build covered tunnels or perhaps a bridge or bypass around the edge of the forest and not through it. Wildlife corridors are one possible solution.

. For your graduate research you have chosen to study the recolonization of disturbed communities of sessile marine invertebrates like those you studied in lab. From observing a time series of plastic panels that have been submerged for varying lengths of time you observe that panels deployed for short periods of time are dominated by colonial sea squirts, whereas those left out for longer periods of time are dominated by solitary seasquirts. Describe an experiment you could perform to test whether the facilitation, inhibition or tolerance model of succession is operating. Draw a graph of your expected experimental results for each model of succession.

Compare plates at different time periods: one at three months, one at six months, one a nine months. Colonists are typically r-‐‐selected species— organisms that can grow quickly and reproduce a lot. As time passes, more K-‐‐ selected organisms start to colonize, and then at the latest time period (what is sometimes called the climax community) the habitat it typically dominated by K-‐‐ selected species. Pretty much all the r-‐‐selected species have been outcompeted and thus excluded from the habitat. Colonial sea squirts: Early pioneer species Solitary Seasquirts- Late Successional Species 1.Facilitation:Ulva could modify the environment to make it more suitable for Gigartina 2. Inhibition:Ulva may be excluding Gigartina but is removed by biotic or abiotic stresses 3. Tolerance: Gigartina is slower growing, and it just takes it longer to dominate the community.

Not all the production at one trophic level makes it to the next. Explain the main sinks for energy as it flows from producer to incorporation into new consumer biomass. Explain how and why the relative size of these sinks might change as a function of (1) consumer trophic level and (2) mode of thermoregulation (endotherm vs. ectotherm).

Conversion rates at each step depend on: 1. food quality of prey (low quality leads to low assimilation, most defecated) 2. metabolic demands of consumer (endotherms spend most assimilated energy on maintaining body temperature). Endotherms convert less energy to next level.

What are dead zones and why do they commonly form near the mouths of large rivers? Would heavy rainfall years expand or contract these dead zones? Explain your answer.

Dead zones occur when large amounts of nutrients are deposited along the coastline from rain washing nutrients downstream. Nutrients fuel rapid growth of algae (algal blooms) which eventually die and are decomposed by bacteria which use up all of the oxygen in the water, creating hypoxic conditions. This is called eutrophication. Heavy rainfall makes these conditions worse because it creates more runoff which carries more fertilizers into the ocean.

What is ecological efficiency? B. Give an average value of ecological efficiency for most ecosystems. C. Explain how ecological efficiency can place an upper limit on the number of trophic levels in an ecosystem.

Ecological efficiency = Transfer of Energy= Production at level n/Production at level n-1 = exploitation efficiency (% of prey production ingested) x assimilation efficiency (% of ingested prey that is assimilated) x production efficiency (% of assimilated prey that is converted to consumer biomass) B. AVERAGE ~ 10% (but ranges from 1% to 25%). C. If too much energy is lost with each change in level up the food chain, then there is not enough energy left to sustain another trophic level, due to energy spent digesting/assimilating food, etc.

Ecosystem A has a primary production of 1000 g C m-‐‐2 y-‐‐1 and ecological efficiency of 10%Ecosystem B has a primary production of 300 g C m-‐‐2 y-‐‐1 and ecological efficiency of 20%-‐‐which ecosystem will have more production at the carnivore trophic level?-‐‐which ecosystem is more likely to contain endothermic consumers?

Ecosystem B is more likely to have more carnivore production. Carnivores occupy the 3rd trophic level and higher, if you use the starting primary production units of energy from both ecosystems and multiply them by their ecological efficiency you will find that at the 3rd trophic level that ecosystem B has 12 units of energy while ecosystem A only has 10, so there will be more carnivore production in ecosystem B.

If forest is fragmented into 4 equal sized subregions, what happens to the edge to area ratio for this landscape? What is this effect called and how does it influence the environment of the patch and its ability to support species that live only in intact forested habitat?

Edge effect. With an increase of percentage of patch influenced by edge effects, area decreases and edges increase. With that, there's a lot of "edge" habitat and it may not support larger organisms. Interior habitat and species decreases. Edge habitat and species increase. Edges also serve as barriers to dispersal. Corridors provide access for some interior species. This is why isolated patches lose species more quickly than connected patches.

Explain how fishing can exert selection on size at maturity. What type of selection is this? What is the observed evolutionary response in fish? How might this slow down recovery of fish stocks, even if fishing is stopped altogether?

Fishing favors larger sized fish, so exerts directional selection to increase frequency of smaller fish in the gene pool which produce less eggs, lowers survival and growth rate. Even if fishing is stopped altogether, recovery will be slow because previous fishing has reduced the variation of size within fish population, selecting against large fish and limit fish size to smaller fish with lower fecundity and overall survivorship.

Distinguish between the fundamental and realized niche. B. Draw a hypothetical fundamental niche for a species of your choice on 2 niche axes. C. use this diagram to depict how niche shrinking and niche expanding factors can modify the fundamental niche to produce the realized niche.

Fundamental niche is the total possible available space for the species, the generalized requirements of the species, the abiotic charcateristics. The physical conditions under which a species can persist. The realized niche is the alteration of fundamental niche by species interactions and other biotic features. It occurs over a narrower range of nutrients due to competition from other species. Sometimes the fundamental niche grows from positive interactions such as vector-aided dispersal, predator refuge, cleaner mutualisms, and habitat amelioration

What is the paradox of the plankton and how can this apparent paradox ultimately be resolved?

How can so many species of algae coexist in the plankton when (1) the environment is so homogeneous and (2) they all compete for essentially the same resources? -Plankton communities are dynamic and conditions are not as homogeneous as we think; conditions rarely favor one species long enough for it to exclude others. Species coexist when resources are fluctuating; fluctuating environment prevents competitive exclusion. -Can be resolved by putting constant flow vs. fluctuating flow of nutrients (silicon and phosphorous)

1. A. Draw a graph to depict how species diversity varies with latitude. B. Describe three general hypotheses to explain this pattern and be able to briefly summarize the evidence for/against each.

Hypothesis: topics have higher K for species Pro: recent evidence suggests there is greater coexistence of sister species in the tropics and this is correlated with higher Net Primary Productivity (NPP) CON: More resources does NOT necessarily mean more species. Increased nutrients leads to higher productivity and biomass, but decreased diversity and increased competitive dominance. There isn't always a latitudinal gradient in productivity (oceans) that matches the latitudinal gradient in diversity. tropics have greater speciation rates pro:The tropics are a "cradle" of diversity —in other words,the tropics are where species tend to be born.Reasoning: Higher mutation rates. Species interactions relatively more important in tropics; interactions potent selective forces BUT no effect of molecular evolution on species richness was detected tropics have been around longer and there has been more time for speciation

Why might natural selection favor variants of a disease that are LESS virulent? Describe one example of this phenomenon.

If a disease is too virulent it will kill its host before it can affect others in the population, and will not live longer or reproduce. Example: myxoma virus and rabbits in Australia.

How do you think species diversity would change when you increase the mean amount of available resources vs. increasing the variation in resource types or amounts? Provide one example to support your reasoning in each case.

Increasing mean amount: Adding resources decreases diversity. More biomass fewer species. Graph comparing nutrients and diversity i. At low end adding nutrients will increase diversity; ii. At the midzone adding nutrients might decrease diversity iii. At the high end adding nutrients might not change the number of species. Furthermore, the species that already used those resources effectively will continue to do so. So merely increasing the mean amount of available resources will just aid the growth and prominence of the already successful species. "Increased nutrients leads to higher productivity and biomass, but decreased diversity and increased dominance" (lecture 5/16) increasing variation in resource types: Increasing the variation of resources might create more niches on which species can specialize.

What is meant by indirect effects B. Give an example of an indirect effect. C. Give an example of an indirect effect in a food web.

Indirect effect: effect of one species on another through its effect on a third (keystone and foundation species). Example: removing plants from a cougar/rabbit/plant cascade will cause the cougar population to decline because the rabbit population declines

Distinguish between complementarity and biological insurance as mechanisms underlying diversity effects by giving an example of each and clearly discussing the biological characteristics of the species that contribute to diversity effects in both cases.

Insurance:If an ecosystem contains more species then it will have a greater likelihood of having redundant stabilizing species, and it will have a greater number of species that respond to disturbances in different ways. This will enhance an ecosystem's ability to buffer disturbances. Complementarity: Plant species coexistence is thought to be the result of niche partitioning, or differences in resource requirements among species. By complementarity, a more diverse plant community should be able to use resources more completely, and thus be more productive. Also called niche differentiation.

compare and contrast, using a phylogeny from lecture or the book, the differences between monophyletic, paraphyletic, and polyphyletic clades/taxa. Why are Reptilia without birds (Aves) paraphyletic? Why do evolutionary biologists aim to name only monophyletic taxa? Why are non-monophyletic taxa a problem? Do sister species represent a monophyletic taxon?

Monophyletic clades are taxonomic groups that include ALL of the taxa/species descended from a specific common ancestor. Paraphyletic clade: a taxonomic group that excludes some of the descendants from a specific common ancestor. Polyphyletic clade: a taxonomic group that does not contain the most recent common ancestor of its members. -Scientists aim for monophyletic because it includes all of the species that descended from a single ancestor and non-monophyletic are a problem because it excludes some of the descendants from the common ancestor. Sister species represent a monophyletic taxon. -Birds accumulated tons of phenotypic and genotypic variation and evolved quickly. Birds are also endotherms like mammals, other than that, birds are clearly descendants from the reptilian ancestors. Feathers are modified scales, embryo development is similar, eggs are similar, etc.

How does natural selection versus genetic drift act to promote the evolution of intrinsic barriers to gene exchange in allopatric (both vicariance and peripatric/dispersal modes) versus parapatric versus sympatric models of speciation?

Natural selection exposes the population to intrinsic barriers (pre and post zygotic). In peripatric speciation genetic drift plays a very large role because speciation is generally driven by founder effects. Because of the small size of these founders, drift enhances the rate at which species can diverge, though selection is still obviously important. In vicariance, parapatric, and sympatric speciation, drift plays less of a role and diversifying selection is the main cause.

. A. Name two factors that determine the maximum number of trophic levels in an ecosystem. B. For an equivalent change in magnitude, which of these two has a stronger effect on the amount of energy available to top consumers? Explain your answer.

Number of levels limited by available energy (number of organisms) and efficiency among energy transfer in chain. Even if the energy efficiency is high, you will not have a 4th trophic level if your primary producer base is really small.

What one factor typically MOST limits primary production in the following environments: A.open ocean B. terrestrial forest? Why?

Phosphorus is limiting in freshwater because phosphorus binds tightly to clay particles on land and so it is in short supply in freshwater. -Nitrogen is limiting in marine and terrestrial because on land nitrogen is easily washed out of the soil and into lakes and rivers because it does not bind tightly to soil

What is the refuge approach to slowing unwanted evolution?

Refuges can maintain desirable genotypes in the system and reduce the fitness differentials between desirable and undesirable genotypes. •Promote the presence of desirable genotypes to slow unwanted adaptation •Reduce the strength of selection, make it variable in space or time •Minimize the difference in fitness between desirable and undesirable genotypes Provide harvest refuges to maintain genetic diversity, to reduce negative evolutionary consequences of trophy hunting. Management strategies should protect some fast‐growing males (refugia)- ensure that high‐quality males have sufficient opportunity to breed before being harvested

ympatric speciation is generally thought to be a rare event because sympatry should promote gene flow. Explain clearly the evidence that speciation occurred sympatrically in the crater lake cichilid fish inhabiting Barombi Mbo in Cameroon. In particular, explain how the phylogenetic relationships of the 11 species of cichlids in this lake support the argument for sympatric speciation. How does this contrast with the phylogenetic evidence for vicariant allopatric speciation in snapping shrimp? Be sure that you can look at a phylogenetic tree and understand whether its structure is consistent with sympatric versus allopatric scenarios for the evolution of reproductive isolation.

Speciation among the crater lake cichilid fish happened because the 11 species diverged in sympatry (overlap). Based on the phylogeny, the 11 species are monophyletic. The mechanism used was Multiple Niche Polymorphism - genetic variants in population consume different prey that select for different traits. This subdivides the population, selecting against mates that don't specialize on what they specifically eat (positive assortative mating occurs). Results in genetic differences and reproductive isolation. In the cichlids, we see that all 11 of these lake species are sister species. When we see sister species among species that are all inhabiting the same area, it suggests sympatric speciation The association of a certain microhabitat, with a particular feeding niche, and the preference to mate with individuals of their own kind reduces gene flow to such an extent that in fact these species of cichlids have been able to diverge within the lake despite their being the potential for gene flow. → Their behaviors reduce gene flow sort of like an extrinsic barrier. - For snapping shrimp, there was a physical barrier to divide a species into two or more populations where they can't freely exchange genes (allopatry). Isthmus of Panama shut off gene flow between the Pacific Ocean and Caribbean Sea (vicariant event). Seven sister species in the shrimp resulted on opposite sides of barrier (they are not monophyletic). If we look at the snapping shrimp's phylogeny, we see that the majority of sister species are inhabiting opposite sides of the Isthmus of panama. When we see sister species among species that are living in distinctly different areas, it suggests allopatric speciation

A. Name and describe the three "models" or "mechanisms" of succession. B. Be able to relate an example of succession in a real community and explain how successional change in that community is determined by one or more of these mechanisms.

Succession: Predictable changes in community composition through time. a.Facilitation: when pioneer species needed for subsequent colonization of habitat by modifying environment (Ex: Alder trees fix nitrogen in soil, improving conditions for the growth of spruces). b.Inhibition: when pioneer species inhibits subsequent colonization of habitat by making environment less suitable (Ex: Ulva and Gigartina) c.Tolerance: Early-successional species neither increase nor reduce rates of recruitment and growth of later-successional species. Species sequence is solely a function of life history. Late-successional species arrive, then grow slowly Late-successional spp. are able to grow and reproduce despite the presence of early- successional spp.

Explain the relationship between energy flow and biomass at different trophic levels in aquatic and terrestrial ecosystems.

Terrestrial biomass generally decreases at each higher trophic level (plants, herbivores, carnivores). Examples of terrestrial producers are grasses, trees and shrubs. These have a much higher biomass than the animals that consume them. The level with the least biomass are the highest predators in the food chain Ocean biomass, in a reversal of terrestrial biomass, can increase at higher trophic levels. In the ocean, the food chain typically starts with phytoplankton. Marine environments can have inverted biomass pyramids. In particular, the biomass of consumers (fish) is larger than the biomass of primary producers. The majority of the biomass in open ocean communities lies in the animals and not the plants. In terrestrial systems plants have majority biomass.

Describe the intermediate disturbance hypothesis (IDH) and use this hypothesis to predict how diversity will change throughout the course of succession.

The Intermediate Disturbance Hypothesis states that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At high levels of disturbance, all species are at risk of going extinct. At intermediate levels of disturbance, diversity is thus maximized because species that thrive at both early(r) and late(k) successional stages can coexist.

Using a specific example of an interspecific interaction from lecture, describe how the same two species can interact to produce a range of outcomes, from positive (facilitative) to negative (competitive or consumptive). B. What components of the physical or biotic environment must change to cause this switch?

The galagos finches are one example of interspecific interactions. living on their own the birds have simular beak sizes but when they live on the same island they undergo character displacement. Mycorrhizal fungi with plants - based on nutrient availability and water, the fungi's effect on the plant can range from mutualism (at low nutrient/water in soil) to commensalism (medium nutrient/water - fungus benefits while plant doesn't really need the fungus anymore) to parasitism (at high nutrients/water, fungus steals plant's carbon, while plant definitely does not need the fungus anymore).

What are life history characteristics of many pecies that typically exhibit 'unwanted' evolution like resistance to antibiotics? What are life history characteristics of species that are most threatened by human activities?

The life history of species that typically experience "unwanted" evolution are r-selected species/Early successional species like insects who develop resistance to pesticides. And the life histories of species most affected by human activity would be the K-selected species like the elephant-tusk example.

Describe an example of the effect of human-‐‐induced climate change on the distribution and abundance of species.

The oceans of the world have absorbed almost half of the CO2 emitted by humans from the )burning of fossil fuels. More acidic ocean water dissolves calcium and reduces its availability for absorption.Excess carbon in the ocean is causing the pH to lower. Many ocean creatures rely on calcium for their shells and support. Snail growth in acidified ocean water is greatly reduced. This is called ocean acidification. CO2 is easily absorbed in H20 reducing the amount of carbonate ions available for calcifying organisms. Resulting in brittle shells, disrupted life cycles of those organisms especially in their juvenile states, and dissolving corals leading to Coral Bleaching. (http://www.whoi.edu/OCB-OA/page.do?pid=112216)

Two closely related grasshopper species occur sympatrically. No hybrids have been reported in nature. However, when an evolutionary biologist brings the two species into the lab, she discovers that they can hybridize to produce fertile offspring. How can you explain these observations? Should the grasshoppers be considered separate species?

They were ecologically isolated. Even though they occupied the same habitat they did not come across each other and therefore did not mate with each other. They are considered different species since they do not produce viable and fertile offspring in the wild - they do not freely exchange genes in the wild.

2. Explain why positive interactions play a prominent role under "stressful" conditions. Draw a graph depicting how the strength of positive interactions changes along some environmental stress gradient (predation pressure, physical stress, etc).

Under stressful conditions, positive interactions can help mitagate the effects of those negative interactions. These interactions are not preformed in an attempt to help the other species but beacuse without them, their survival is threatened. These interactions can also help shape the size of the fundamental niche. Furthermore, studies show that these types of positive interactions increase as the stress level increases

1. Define the following terms: mutualism, commensalisms, positive interactions, foundation species, keystone species

mutualism: symbiosis that is beneficial to both species invloved commensalism: a type of symbiosis in which one species is benefited but one species is neutrally affected foundation species: Species that have a strong role in structuring an ecosystem Keystone species: A species that has disproportionally large affect on the ecosystem relative to its abundance

What are the characteristics of typical early successional species and late successional species?

r species - pioneer: many small propagules, are good dispersers and thrive under low competition later successional species aka k species may be facillatated, inhibiated, or simply toerate the early successional species. They are less tolerant, good competators, mature and establish themselves slowly, fewer propagules

7. Define and given an example of the following terms: trophic cascade, indirect effect. Draw a real food web (one from lecture or someplace else) that depicts each of these.

trophic Cascade: Occur when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore). Trophic cascades are an example of "top-down" regulation of community composition and plant biomass (top predator effects on trophic levels beneath it). Example: Urchins can overgraze kelps, leaving nothing but crustose coralline algae that are grazer-resistant. When otters are present, urchin densities are reduced, increasing kelp biomass. Indirect Effect: effect of one species on another through its effect on a third.