45.E: Population and Community Ecology (Exercises)
45.1: Population Demography
Populations are dynamic entities. Populations consist all of the species living within a specific area, and populations fluctuate based on a number of factors: seasonal and yearly changes in the environment, natural disasters such as forest fires and volcanic eruptions, and competition for resources between and within species. The statistical study of population dynamics, demography, uses a series of mathematical tools to investigate how populations respond to changes in their environments.
Review Questions
Which of the following methods will tell an ecologist about both the size and density of a population?
- mark and recapture
- mark and release
- quadrat
- life table
- Answer
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C
Which of the following is best at showing the life expectancy of an individual within a population?
- quadrat
- mark and recapture
- survivorship curve
- life table
- Answer
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D
Humans have which type of survivorship curve?
- Type I
- Type II
- Type III
- Type IV
- Answer
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A
Free Response
Describe how a researcher would determine the size of a penguin population in Antarctica using the mark and release method.
- Answer
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The researcher would mark a certain number of penguins with a tag, release them back into the population, and, at a later time, recapture penguins to see what percentage of the recaptured penguins was tagged. This percentage would allow an estimation of the size of the penguin population.
45.2: Life Histories and Natural Selection
A species’ life history describes the series of events over its lifetime, such as how resources are allocated for growth, maintenance, and reproduction. Life history traits affect the life table of an organism. A species’ life history is genetically determined and shaped by the environment and natural selection.
Review Questions
Which of the following is associated with long-term parental care?
- few offspring
- many offspring
- semelparity
- fecundity
- Answer
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A
Which of the following is associated with multiple reproductive episodes during a species’ lifetime?
- semiparity
- iteroparity
- semelparity
- fecundity
- Answer
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B
Which of the following is associated with the reproductive potential of a species?
- few offspring
- many offspring
- semelparity
- fecundity
- Answer
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D
Free Response
Why is long-term parental care not associated with having many offspring during a reproductive episode?
- Answer
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Parental care is not feasible for organisms having many offspring because they do not have the energy available to take care of offspring. Most of their energy budget is used in the formation of seeds or offspring, so there is little left for parental care. Also, the sheer number of offspring would make individual parental care impossible.
45.3: Environmental Limits to Population Growth
Although life histories describe the way many characteristics of a population (such as their age structure) change over time in a general way, population ecologists make use of a variety of methods to model population dynamics mathematically. These more precise models can then be used to accurately describe changes occurring in a population and better predict future changes.
Review Questions
Species with limited resources usually exhibit a(n) ________ growth curve.
- logistic
- logical
- experimental
- exponential
- Answer
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A
The maximum rate of increased characteristic of a species is called its ________.
- limit
- carrying capacity
- biotic potential
- exponential growth pattern
- Answer
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C
The population size of a species capable of being supported by the environment is called its ________.
- limit
- carrying capacity
- biotic potential
- logistic growth pattern
- Answer
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B
Free Response
Describe the rate of population growth that would be expected at various parts of the S-shaped curve of logistic growth.
- Answer
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In the first part of the curve, when few individuals of the species are present and resources are plentiful, growth is exponential, similar to a J-shaped curve. Later, growth slows due to the species using up resources. Finally, the population levels off at the carrying capacity of the environment, and it is relatively stable over time.
45.4: Population Dynamics and Regulation
The logistic model of population growth, while valid in many natural populations and a useful model, is a simplification of real-world population dynamics. Implicit in the model is that the carrying capacity of the environment does not change, which is not the case. The carrying capacity varies annually: for example, some summers are hot and dry whereas others are cold and wet. In many areas, the carrying capacity during the winter is much lower than it is during the summer.
Review Questions
Species that have many offspring at one time are usually:
- r -selected
- K -selected
- both r - and K -selected
- not selected
- Answer
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A
A forest fire is an example of ________ regulation.
- density-dependent
- density-independent
- r -selected
- K -selected
- Answer
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B
Primates are examples of:
- density-dependent species
- density-independent species
- r -selected species
- K -selected species
- Answer
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D
Free Response
Give an example of how density-dependent and density-independent factors might interact.
- Answer
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If a natural disaster such as a fire happened in the winter, when populations are low, it would have a greater effect on the overall population and its recovery than if the same disaster occurred during the summer, when population levels are high.
45.5: Human Population Growth
Although humans have increased the carrying capacity of their environment, the technologies used to achieve this transformation have caused unprecedented changes to Earth’s environment, altering ecosystems to the point where some may be in danger of collapse. The depletion of the ozone layer, erosion due to acid rain, and damage from global climate change are caused by human activities. The ultimate effect of these changes on our carrying capacity is unknown.
Review Questions
A country with zero population growth is likely to be ________.
- in Africa
- in Asia
- economically developed
- economically underdeveloped
- Answer
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D
Which type of country has the greatest proportion of young individuals?
- economically developed
- economically underdeveloped
- countries with zero population growth
- countries in Europe
- Answer
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B
Which of the following is not a way that humans have increased the carrying capacity of the environment?
- agriculture
- using large amounts of natural resources
- domestication of animals
- use of language
- Answer
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B
Free Response
Describe the age structures in rapidly growing countries, slowly growing countries, and countries with zero population growth.
- Answer
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Rapidly growing countries have a large segment of the population at a reproductive age or younger. Slower growing populations have a lower percentage of these individuals, and countries with zero population growth have an even lower percentage. On the other hand, a high proportion of older individuals is seen mostly in countries with zero growth, and a low proportion is most common in rapidly growing countries.
45.6: Community Ecology
Populations rarely, if ever, live in isolation from populations of other species. In most cases, numerous species share a habitat. The interactions between these populations play a major role in regulating population growth and abundance. All populations occupying the same habitat form a community: populations inhabiting a specific area at the same time. The number of species occupying the same habitat and their relative abundance is known as species diversity.
Review Questions
The first species to live on new land, such as that formed from volcanic lava, are called ________.
- climax community
- keystone species
- foundation species
- pioneer species
- Answer
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D
Which type of mimicry involves multiple species with similar warning coloration that are all toxic to predators?
- Batesian mimicry
- Müllerian mimicry
- Emsleyan/Mertensian mimicry
- Mertensian mimicry
- Answer
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B
A symbiotic relationship where both of the coexisting species benefit from the interaction is called ________.
- commensalism
- parasitism
- mutualism
- communism
- Answer
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C
Free Response
Describe the competitive exclusion principle and its effects on competing species.
- Answer
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The competitive exclusion principle states that no two species competing for the same resources at the same time and place can coexist over time. Thus, one of the competing species will eventually dominate. On the other hand, if the species evolve such that they use resources from different parts of the habitat or at different times of day, the two species can exist together indefinitely.
45.7: Behavioral Biology: Proximate and Ultimate Causes of Behavior
One goal of behavioral biology is to dissect out the innate behaviors, which have a strong genetic component and are largely independent of environmental influences, from the learned behaviors, which result from environmental conditioning. Innate behavior, or instinct, is important because there is no risk of an incorrect behavior being learned. They are “hard wired” into the system. On the other hand, learned behaviors, although riskier, are flexible, dynamic, and can be altered.
Review Questions
The ability of rats to learn how to run a maze is an example of ________.
- imprinting
- classical conditioning
- operant conditioning
- cognitive learning
- Answer
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D
The training of animals usually involves ________.
- imprinting
- classical conditioning
- operant conditioning
- cognitive learning
- Answer
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C
The sacrifice of the life of an individual so that the genes of relatives may be passed on is called ________.
- operant learning
- kin selection
- kinesis
- imprinting
- Answer
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B
Free Response
Describe Pavlov’s dog experiments as an example of classical conditioning.
- Answer
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Dogs salivated in response to food. This was the unconditioned stimulus and response. Dogs exposed to food had a bell rung repeatedly at the same time, eventually learning to associate the bell with food. Over time, the dogs would salivate when the bell was rung, even in the absence of food. Thus, the bell became the conditioned stimulus, and the salivation in response to the bell became the conditioned response.