Deck 55: Population Ecology

Question 1

Refer to figure 56.13. Given a trade-off between current reproductive effort and future reproductive success (the so-called cost of reproduction), would you expect old individuals to have the same "optimal" reproductive effort as young individuals

Answer 1

Natural selection favors traits that maximize the number of surviving offspring in next generation. Two factors that affect this trait: how long an individual lives, and how many young it produces each year. All organisms allocate resources either to current reproduction or to increasing their prospects of surviving and reproducing at later stages. The complete life cycle of an organism is called life history. All life histories involve significant trade-offs. As resources are in short supply, a change that increases reproduction may decrease survival and reduce future reproduction. Birds that have more offspring each year have a higher probability of dying during that year or producing smaller clutches the following year. On the other hand, individuals that delay reproduction may grow faster and larger, enhancing future reproduction. Ecologists refer to the reduction in future reproductive potential resulting from current reproductive efforts as the cost of reproduction.
Natural selection will favor the life history that maximizes lifetime reproductive success. When the cost of reproduction is low, individuals should produce as many offspring as possible because there is little cost. Low costs of reproduction may occur when resources are abundant and may also be relatively low when overall mortality rates are high. In the latter case, individuals may be unlikely to survive to the next breeding season, so the incremental effect of increased reproductive efforts may have little effect on future survival. Alternatively, when costs of reproduction are high, lifetime reproductive success may be maximized by deferring or minimizing current reproduction to enhance growth and survival rates. This situation may occur when costs of reproduction significantly affect the ability of an individual affect the ability of an individual to survive, or decrease the number of offspring that can be produced in future.

Question 2

Geographic ranges of populations

A) were static until human disturbance led to extinction and introductions.
B) are never affected by the distribution and abundance of predators.
C) do not respond to long-term climatic changes.
D) None of the above.

Answer 2

(A) A population's geographical distribution is termed its range. Population ranges are not static but change through time. These changes occur either due to environmental changes or populations expand their ranges when they are able to circumvent inhospitable habitat to colonize suitable, previously unoccupied areas. By altering the environment, humans have allowed some species to expand their ranges and move into areas they previously did not occupy. Humans have also served as an agent of dispersal for many species.

Question 3

Refer to figure 56.14. Because the number of offspring that a parent can produce is often a trade-off with the size of individual offspring, many circumstances lead to an intermediate number and size of offspring being favored. If the size of an offspring was completely unrelated to the quality of that offspring (its chances of surviving until it reaches reproductive age), would you expect parents to fall on the left or right side of the x -axis (clutch size) Explain.

Answer 3

In natural selection, the number of offspring produced is not as important as how many of those offspring survive to reproduce. As the amount of energy invested in offspring is limited, a balance must be reached between the number of offspring produced and the size of each offspring. This trade-off was demonstrated in side-blotched lizard, which normally lays 4-5 eggs at a time. When some of the eggs are removed surgically early in the reproductive cycle, the female lizard produces only one to three eggs, but supplied each of these eggs with greater amount of yolk, producing eggs and, subsequently, hatchlings that are much larger than normal. However when yolk was removed from eggs, smaller young would be produced. The size of offspring critically affects their survival prospects - larger offspring have a greater chance of survival. Producing many offspring with little chance of survival might not be the best strategy, but producing a single, extraordinary robust offspring also would not maximize the number of surviving offspring. Rather, am alternative situation, in which several fairly large offspring are produced, should maximize the number of surviving offspring. So, if the size of an offspring is completely unrelated to the quality of that offspring then parents would fall on the right side of the x-axis.

Question 4

Source-sink metapopulations are distinct from other types of metapopulations because

A) exchange of individuals only occurs in the former.
B) populations with negative growth rates are a part of the former.
C) populations never go extinct in the former.
D) all populations eventually go extinct in the former.

Question 5

Refer to figure 56.26. Would increasing the mean generation time have the same kind of effect on population growth rate as reducing the number of children that an individual female has over her lifetime Which effect would have a bigger influence on population growth rate Explain

Question 6

I would expect the potential for social interactions among individuals to be maximized when individuals

A) are randomly distributed in their environment.
B) are uniformly distributed in their environment.
C) have a clumped distribution in their environment.
D) are non-randomly distributed in their environment.

Question 7

When ecologists talk about the cost of reproduction they mean

A) the reduction in future reproductive output as a consequence of current reproduction.
B) the amount of calories it takes for all the activity used in successful reproduction.
C) the amount of calories contained in eggs or offspring.
D) None of the above

Question 8

A life history trade-off between clutch size and offspring size

A) means that as clutch size increases, offspring size increases.
B) means that as clutch size increases, offspring size decreases.
C) means that as clutch size increases, adult size increases.
D) means that as clutch size increases, adult size decreases.

Question 9

The difference between exponential and logistic growth rates is

A) exponential growth depends on birth and death rates and logistic does not.
B) in logistic growth, emigration and immigration are unimportant.
C) that both are affected by density, but logistic growth is slower.
D) that only logistic growth reflects density-dependent effects on births or deaths.

Question 10

Humans are an example of an organism with a type I survivorship curve. This means

A) mortality rates are highest for younger individuals.
B) mortality rates are highest for older individuals.
C) mortality rates are constant over the life span of individuals.
D) the population growth rate is high.

Question 11

According to the Population Reference Bureau (2002), the worldwide intrinsic rate of human population growth ( r ) is currently 1.3%. In the United States, r = 0.6%. How will the U.S. population change relative to the world population

A) The world population will grow, while the population of the United States will decline.
B) The world population will grow, while the population of the United States will remain the same.
C) Both the world and the U.S. populations will grow, but the world population will grow more rapidly.

Question 12

The logistic population growth model, dN / dt = rN [( K - N )/ K ], describes a population's growth when an upper limit to growth is assumed. As N approaches (numerically) the value of K

A) dN / dt increases rapidly.
B) dN / dt approaches 0.
C) dN / dt increases slowly.
D) the population becomes threatened by extinction.

Question 13

Which of the following is an example of a density-dependent effect on population growth

A) An extremely cold winter
B) A tornado
C) An extremely hot summer in which cool burrow retreats are fewer than number of individuals in the population
D) A drought

Question 14

Refer to figure 56.8. What are the implications for evolutionary divergence among populations that are part of a metapopulation versus populations that are independent of other populations

Question 15

When individuals respond physiologically to an environmental change

A) natural selection has occurred.
B) differences among individuals could lead to evolution by natural selection.
C) they cannot respond simultaneously through changes in behavior and morphology.
D) None of the above.