Download Page 1 of 7 Biology 372 Name

 Biology 372 General Ecology with Jesse Brunner Name:________________________________ EXAM 2 Read questions carefully before answering. If you need clarification, just raise your hand. For multiple choice and True/False questions, please circle the best answer. For short answers, please write clearly and concisely. There is no need to repeat the question in your answer, but please write in full sentences with proper grammar. Limit your answers to the space available. Where appropriate use diagrams to illustrate your answers. Remember, you are taking an ecology test, so use the appropriate mechanisms, rules of thumb, and always, always connect the logical dots for us. Calculators are allowed. Smart phones or other “smart” devices are not allowed. The exam will end at 10:20am. Potentially useful equations €
(a) N t = N 0 λt (b) λ = N t+1 N t = exp(r ) (c) dN
= rN dt
€
€
(d) (e) €
€ (f) (g) € (h) # N&
dN
= rN%1 − ( $ K'
dt
(i) R0 = ∑ lx mx T=
∑ xl m
x
x
R0
r = ln(R0 ) /T €
⎛ N + α12 N 2 ⎞
dN1
= rN1⎜1 − 1
⎟,
K1
⎝
⎠ € (j) dt
⎛ N + α 21N1 ⎞
dN 2
= rN 2 ⎜1 − 2
⎟
dt
K2
⎝
⎠
dP
= cP(1 − P) − eP
dt
lx = n x /n 0
mx = bx /n x
€
dN prey
= rN prey − aN prey N predators,
€ (k) dt
dN predators
= abN prey N predators − mN predators
dt
€ Page 1 of 7 Probability of surviving 1 year Q1: In the logistic model of population growth, the strength of intraspecific competition will change: a) r c) Both b) K d) neither Q2: Predators or parasites might help competing species coexist by: a) Reducing the density of one or more of the species b) Altering the behavior (e.g., foraging behavior) of one or more species c) Excluding both species from part of their collective range d) a & b e) b & c Q3a: True or False: Annual plants (those that live only a single year) tend to devote more of their energy reserves to producing many more seeds than a comparable perennial plant does in a given year. (2pts) Q3b: Why? (4pts) Annuals do not need to invest in survival (they’re dying anyway) 2pts, perennials keep some reserves / invest in survival until the next reproductive event (or future resources are uncertain, so they invest less) 2pts. Q4: True or False: An organism’s realized niche need not overlap with its fundamental niche. Q5a: Draw on the axes (to the right) the relationship an ecologist would expect between the size of a seed and the chances that the germinated plant will survive a year, all else equal (i.e., don’t get too creative!). (2pts) Q5b: In two sentences, explain why an ecologist would expect this relationship. (I.e., explain your Size of seed reasoning in general, but completely.) (4pts) Larger seeds have more resources to devote to growth, maintenance and survival. They are thus better able to weather severe conditions, compete for resources, etc. Q5c: Given this relationship (i.e., higher survival at a certain seed size), why do we observe a whole range of seed sizes among plants? (Just provide one clear, direct answer.) (4pts) There is a trade-­‐off between seed size (and higher survival and competitive ability) and dispersal ability and/or the number of seeds (thus opportunities to establish) that a plant can produce. Or some other clear explanation. Page 2 of 7 Q6a: In this graph of the number (bars) and causes (stacked area graph) of human deaths at various ages in the developed world, it is clear that most mortality occurs after ~50 years of age. How do these high levels of mortality affect the growth of the human population in the developed world? (3pts) Why? (3pts) Most of these sources of mortality occur well after the reproductive age of humans and so they would have very little impact on human growth rates. (However the lower mortality rates early on, e.g., from accidents, does have some impact on the population’s growth rate) Q6b: Given this mortality data, sketch on these axes the survival curve for this human population. (4pts) Q6c (bonus): Why hasn’t natural selection over the last several hundred thousand years minimized the occurrence of (or removed the genes for) cancer and circulatory disease? (Think of this in terms of life history.) (3 pts) Since these causes of mortality occur after individuals are able to reproduce, they do not influence one’s individual fitness (although there is a hypothesis that grandmothers and grandfathers increase their inclusive fitness by caring for grandkids). Page 3 of 7 Q7a: Using the estimates of carrying capacities and competition coefficients provided in the table, draw the isoclines for species A (solid line) and species B (dashed line). Be sure to label the ends of both lines. Note: you are welcome to color-­‐code the lines as well, but please use the line types I specified. (6 pts). Species A Species B Solid lines Dashed lines KA = 150 KB = 100 αAB = 3 αBA = 1 KB KA/αAB KB/αBA KA Q7b: Now imagine that we place in a habitat 100 individuals of each species. : Draw the trajectory that these two species will follow from this point to a stable equilibrium. (Note: you do not need to include the vectors, but I will not be able to discern your logic, so you will likely not get partial credit if you veer off course for some reason.) (6pts) Q7c: Which species will persist? (2pts) Species B (but should be graded based on what you actually showed) Q7d: Would your answer be different if we started at species A’s carrying capacity and added one of species B? (2pts) Yes (but should be graded based on what you actually showed)
Page 4 of 7 Q8a: Draw on the axes below the graph showing the dynamics of a population starting from N0 = 100 and growing logistically with a carrying capacity of 1500 (solid line). The exact dynamics are not essential; we want to see the appropriate starting and ending values, and the general trend in between. (6pts) Q8b: On your graph, draw an arrow to part of the curve where the overall rate at which the population is growing is highest. (2pts) Q8c: Now, circle the part of the curve where the per capita rate of increase is highest (2pts) Q8d: Draw a dashed line showing what the curve would look like if the intrinsic rate of increase, r, were half as large as in your solid-­‐line (2pts) S8e: What would happen if the strength of competition were twice as strong? (2pts) The carrying capacity would shrink by ~ half Page 5 of 7 Q9a: Using a solid line, draw the isocline for a prey species (e.g., hare) that has a carrying capacity, assuming that the predator (e.g., lynx) has a type III functional response (e.g., prey switching). Use a dashed line to draw the predator isocline (assuming nothing other than what I have told you!). (8pts) Q9b: Draw on the axes below the densities of prey and predators starting at the star and going through time. Make sure you provide enough of the dynamics that I can see what you are thinking will happen! (6pts) Should show damped oscillations (depending on isoclines above) with predators lagging prey ~1/4 cycle Page 6 of 7 Q10: Most people assume that predators (e.g., wolves, grrr!) regulate their prey (e.g., deer)-­‐
—that is, predators keep their prey populations from reaching their carrying capacity. Focusing on the ecology of predation, the host biology, etc., provide one explanations for why this isn't always the case. Hint: you do not need to invoke the Lotka-­‐Volterra models. As always, make sure your logic is clear. (6pts) ∴ Those getting eaten might be weak, diseased, or otherwise likely to die already ∴ Might be demographically unimportant (e.g., post-­‐reproductive individuals) ∴ Might be compensating density dependence such that survival/fecundity of individuals increases to offset loss to population (must either use the term or have the gist of compensation for full points) Age
class (x)
Number
♀ alive
lx
Births
(all ♀s)
mx
l xm x
xlxmx
1
1000
1
0
0
0
0
2
500
0.5
250
0.5
0.25
0.5
3
400
0.4
600
1.5
0.6
1.8
4
50
0.05
100
2
0.1
0.4
Q12a: Finish filling out the life table above for snowshoe hares (4pts), then answer the following questions. Show your work (NOTE: we graded based on your #s) Q12b: How many offspring does the average female produce over her entire life? (3pts) 0.95 Q12c: What is the generation time of this population? (3pts) R0 = ∑lxmx = 0 + 0.25 + 0.6 + 0.1 = 0.95 T = ∑xlxmx / R0 = (0 + 0.5 + 1.8 + 0.4) / 0.95 = 2.7/0.95 = 2.84 Q12d: What is the estimate of the intrinsic growth rate of this population, r? (3pts) r =ln(R0)/T = ln(0.95)/2.84 = -­‐0.018 Q12e: Will this population grow, shrink, or stay the same? (2pts) shrink Q12f: Changing just one aspect of the life history of this organism, how could you reverse the population growth (i.e., from positive to negative, or negative to positive, or constant to growing)? (3pts) Increase survival to reproductive age OR Increase birth rate of those surviving OR lower reproductive age. Page 7 of 7