Flashcards
Midterm 2 Ecology Qs pack. 3
Cards in this deck (24)
- 1Do two species always compete if they live in the same place and share a limiting resource?Yes.
- 2What happens to the strength of competition between two species over evolutionary time? How can you explain this in terms of natural selection acting on individuals of each species? How would it be manifested in the terms of the Lotka- Volterra competition model? ·The strength of competition may diminish (reflected in lower α, β) because those individuals of each species that have lower niche overlap with the other species may have higher fitness as a result.
- 3Categorize the following as exploitative competition, interference competition, apparent competition, or absence of competition a. Lions attack a pack of hyenas and steal a gazelle the hyenas have killed. · b. Predation by lions reduces the gazelle population, causing the hyena population to decrease. · c. In California chaparral communities, sagebrush (Artemisia tridentata) exudes chemicals into the soil which don't harm its own growth, but inhibit the growth of other plant species. · d. Moose tend to decline in places where white-tailed deer are common, because a parasite harbored by the deer is fatal to the moose. ·Exploitation: Species A affects Species B by diminishing the supply of a shared limiting resource (Kangaroo rats, mice, ants reduce one another‘s seed supply)
Interference: Species A affects Species B by reducing Species B’s ability to exploit a limiting resource (Kangaroo rats harass mice)
Apparent competition: Species A affects Species B by increasing the abundance of a shared predator or disease (See moose-deer example in study questions)
a. Interference, bc the lion is directly interfering with hyenas
b. exploitation
c. interference
d. apparent competition, bc they share a predatory disease - 4Species A and B grow in the same region, but Species A is more abundant on cooler north-facing slopes, and Species B is more abundant on warmer south-facing slopes. a. State two rival hypotheses to explain the distribution of species A, one invoking interspecific competition and the other not. · b. Describe an experiment that would test the competition hypothesis. State your treatments, controls, and what outcome would support the hypothesis. ·Competition- A can grow on both slopes but is outcompeted on warm slopes by B Non-competition- A cannot grow on warm slopes regardless of B
Experiment-controls where B is not not removed. Competition is supported if it can grow there but only in absence of B - 5American gray squirrels have invaded England, and the native red squirrel has declined; this may or may not be because of competition. If you couldn't do an experiment, what observational evidence would help you decide whether it's because of competition or not? ·Exploitation: do they share resources that are in short supply? Interference: is the gray squirrel aggressive toward the red squirrel?
- 6List and define each term (symbol) in the Lotka-Volterra competition equations. Then use these terms to express each of the following situations: a. competition is “asymmetric” b. competition is caused by small amount of overlap in resource use c. competition is caused by almost complete overlap in resource use d. species 1 is affected more by species 2 than by itselfa. α < > β
b. α & β small
c. α & β almost 1
d. α > 1 - 7Carefully explain one particular way in which real-world competition might be too complex to predict using the Lotka-Volterra model. ·(1) competition may occur only between close neighbors; (2) the strength of competition may vary in time and/or space; (3) competitors may be held below their joint carrying capacities by predators or disturbances
- 8Draw a graph representing Types I, II, and III functional responses, being sure to label the axes correctly. For the Type III response, describe in words what it means, what causes it, what effect it has on predator-prey dynamics, and why it has this effect.Each predator has a fixed maximum number of prey it can consume per unit time. In addition, each predator consumes fewer prey when prey are scarce. It stabilizes predator-prey dynamics because as the prey population becomes very scarce, a lower percentage of prey are eaten, allowing the prey population to recover.
- 9Starting from the simplest possible assumptions, the Lotka-Volterra model predicts regular cycles in predator and prey (victim) abundance. a.What are two features that can be added to the Lotka-Volterra predation model to stabilize it (i.e. get rid of cycles)? · b. Which of these two features is most compatible with the predator exerting a high degree of control of the prey population? Find an example of a predator- prey interaction in the text (Ch. 14) that shows this feature. ·a. A prey (victim) carrying capacity or a type III functional response
b. type III functional response - 1013. A predatory rotifer preys on a species of Paramecium. The dynamics of this simple laboratory system can be described by the following Lotka-Volterra equations. Find the equilibrium population sizes of predator and victim.#13
3 and 100 - 1114. Because the predators are so efficient at finding prey, we have difficulty maintaining this system in the laboratory. If we increase the size of the container, however, the rotifers have more difficulty finding prey and the system becomes easier to maintain. If the predators are now one-third as efficient at locating prey, what is the new equilibrium population size of predators? Why is it that the system is now easier to maintain?The system is easier to maintain when the predator is inefficient, because the equilibrium predator population is higher, making the predator population less likely to crash to extinction.
- 12What are three features of a predator that enable it to successfully control its prey population? Which of these is most compatible with stable coexistence? (See text, pp. 306-308). ·High r, high K, high searching ability, no self-interference, alternative prey, and Type III functional response are all acceptable answers The Type III functional response is the most compatible with stability
Predator have high Carrying capacity (self-interference) =not compatible - 13Devise an explanation, consistent with what you have learned about predator- victim dynamics, for why lions and other large predators of the Serengeti do not appear to control populations of wildebeests and other large migratory ungulates (see text p. 199). ·these predators appear to have a low carrying capacity set by the availability of resident prey in the dry season
- 14An alternative to the classic theory of biological control, where the predator holds the victim to a low stable equilibrium, is the metapopulation predator-victim model (see text pp. 195-196 and 307-308). Look at book a.Describe in words how this model works. · b. Describe how this model was tested in mites and the results of this test. ·a. Predators may eliminate prey within patches of habitat, but then the predator goes extinct within that patch. Prey survive by colonizing patches where predators are absent, and both species persist in a constant game of hide and seek
b. A mite predator and its mite prey were able to coexist for many weeks in a large set of oranges that were connected by a small amount of mite dispersal. The predator could wipe out the prey on one orange at a time, but not everywhere at once. In contrast, the predator and prey could not coexist in simpler settings, such as sets of oranges that were completely connected or completely unconnected. This result supported the model. - 15What experiment can you use to tell if a distasteful chemical that a plant produces is really a defensive adaptation against herbivores, as opposed to just being a metabolic by-product? ·You can compare the fitness of individuals with higher versus lower levels of this chemical in two treatments: herbivores present and absent. If you find that individuals with more of the chemical have higher fitness in the presence of the herbivores, but also have lower fitness in the absence of the herbivores, it supports the idea that the chemical is a defense.
- 16Some studies have concluded that insect damage has less effect on the fitness of plants than plant traits (such as foliar chemistry) have on the fitness of herbivorous insects. If this is true, how might Ehrlich and Raven’s “coevolutionary arms race theory” of insect-plant interactions need to be modified? ·Plants are unlikely to evolve in response to the opportunity caused by a new anti-insect defense, but insects may still evolve in response to the opportunity caused by overcoming a plant defense
- 17What kinds of defenses do oaks have against Lepidopteran folivores (pp. 215- 216)? How do these defenses affect the insects, and what counteradaptations do the insects show?"See text"
- 18In the ant-acacia mutualism (pp. 216-217), what are the benefits for the ant? What are the benefits for the plant, and what experiment was used to demonstrate them? ·(a) A place to live and specialized food bodies produced by the plant; (b) protection from herbivores; (c) ant removal followed by measurement of herbivory on the acacia trees
- 19What condition must be met for a disease to spread in a population (in both symbols and words)? ·R0 >1, in other words each infected individual must infect >1 new individual
- 20If a disease evolves the ability to go undetected by the host’s immune system, how will this affect the disease’s rate of spread, the threshold population size for the disease to persist, and the fraction of the population that must be vaccinated to stop its spread? ·These quantities will increase, decrease, and increase
- 2125. The simple model for a directly transmitted disease presented by Krebs (pp. 236- 237) finds that R0 = β/γ, where the units of β are individuals per unit time, and the units of γ are time-1. a. What does this model assume about the effects of population size (N) on the rate at which the disease spreads, and what is a reasonable alternative assumption (for a hint, see Figure 13.3 on p. 239)? b. An alternative model that accounts for a higher rate of contact and thus faster disease spread in larger populations is Ro = Nβ/γ. In this model, what is NT, the threshold population size for the disease to spread?a. In this model, N does not affect the rate of spread. Each infected individual contacts a relatively constant number of susceptible individuals, regardless of N. Alternatively, it could be assumed that in larger populations, each infected individual comes into contact with more susceptible individuals, and thus you would need a model in which the disease spread rate also depends on N.
b.For the disease to spread, R0 must be >1. Therefore, it must be true that Nβ/γ > 1, and thus N > γ/β, so NT = γ/β.
Ro(infected individuals) only exceeds as long as N is greater than gamma
>Solving for N so you can find min. Of N which allows disease to spread
N comes into play when an equilibrium is reached
Disease can only spread to a certain number and would only change if pop. is so small, which then changes the rate of spread of disease - 22According to theory, a vectored disease like malaria can be eradicated by reducing the vector (mosquito) population below a certain critical level. Let’s say that human malaria was wiped out from a region when the extent of wetlands was reduced by 50%, but soon afterward, a gold rush caused the human population to triple. Would you expect malaria to return as a result? Explain. · No, because higher human population would still further reduce the vector-to-host ratio, which must reach a critical minimum for a vectored disease to spreadNo, because higher human population would still further reduce the vector-to-host ratio, which must reach a critical minimum for a vectored disease to spread
- 23A classic idea held that “the well-adapted parasite is benign” (p. 251). a. Describe the evidence for and against this idea. · b. What are some traits that diseases can evolve that achieve high fitness of the disease in spite of high virulence? ·a. Some diseases, like myxoma, have been observed to evolve reduced virulence; but many other diseases have remained highly virulent.
b. A high rate of transmission (achieved by high disease reproductive rate or disease-induced behavioral alterations of the host), or a low rate of recovery (achieved by defeating the host immune system or various other means) - 24Under the Red Queen Hypothesis, where would you expect to find more asexual organisms: the humid tropics or desert? Explain. ·In the desert, because there are fewer species of pathogens than in the tropics, and thus less selective pressure to reproduce sexually as a way of (co)evolving pathogen resistance
Think about competition pressures (Nich)
Can never hold still so you have constant change in allele frequencies
“must run as fast as she can just to stay in one place”
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- Flashcards on Midterm 2 Ecology Qs pack. 3, created by Daniel Oropeza on 15/11/2017.
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