Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 39
39.1
1. A habitat is the part of the environment where an organism lives.
2. Population density is the number of individuals of a species in a specific unit area or unit
volume of a habitat.
3. The three kinds of dispersion in a habitat are random dispersion (in which a species is
dispersed without a discernible pattern), uniform dispersion (in which a species is dispersed in a
regular pattern), and clumped dispersion (in which a species is dispersed in groups or clusters).
4. A population will grow when its birth rate is greater than its death rate. It also will grow when
there are many more individuals in the reproductive and pre reproductive years than in the post
reproductive years.
5. The birth rate of a population is determined by the number of individuals of reproductive age in
the population. Birth rate is influenced by how many offspring are produced by each mating, by
the age at which individuals are able to mate, and by the number of times an individual
reproduces in his or her lifetime.
6. In a Type I survivorship curve, most individuals live long lives and then die. In a Type II
survivorship curve, death is constant throughout the life span for the species. In a Type III
survivorship curve, most deaths occur early in life and a few individuals survive to old age.
7. If a population has many individuals in pre-reproductive or reproductive years, the population
will grow. Conversely, if a population has few individuals in these age groups, the population will
not grow.
39.2
1. The per capita rate of increase is the difference between the birth rate and the death rate.
2. Exponential population growth is supported by unlimited space, food, mates, and other
environmental factors that promote population growth.
3. In logistic growth, the population experiences limiting factors in the environment that slow
growth and cause it to eventually level off. In exponential growth, the population increase
continues unchecked and no limiting factors retard it.
4. Environmental resistance is an external force that keeps a population from growing at a
maximal rate. It is anything that inhibits reproduction and immigration, or anything that increases
mortality or emigration. Environmental resistance helps to determine a habitat’s carrying capacity,
the maximum number of individuals of a species that a habitat can support a population.
5. A habitat’s carrying capacity can fluctuate over time, depending upon environmental conditions
such as drought, heavy rainfall, other extreme weather conditions, or catastrophes.
6. Density-dependent factors limit population size when a population reaches a certain size.
Three examples are infectious diseases, predation, and competition. Density-independent factors
limit populations, no matter how large or small they are. Examples are severe weather conditions,
geological catastrophes, floods, and oil spills.
39.3
1. K-selected species have adaptations that result in large body size, long lives, fewer young
produced, much parental care for young, and late maturation. Humans, elephants, and redwood
trees are K-selected species. In contrast, r-selected species have adaptations that result in small
body size, short lives, quick maturation, more young produced, little or no parental care for young,
and early maturation. Most insects and weeds are r-selected species.
2. Studies with guppies have shown that predators can influence populations of their prey, shifting
them towards r-selected traits or, when predation is not a component of the environment, shifting
them towards K-selected traits.
39.4
1. Less-developed countries have the greatest rates of human population growth, while more
developed countries have the lowest rates of human population growth.
2. As a nation passes through the demographic transition it passes through three general stages.
At first, birth and death rates are high so the population does not grow much. Then living
conditions improve and the death rate falls, but the birth rate remains high. The population begins
to increase. Finally, the death rate stays low as the birth rate declines. Now the rate of population
growth slows and may cease.
3. Factors that affect birth and mortality rates are family planning programs, social factors,
economic factors, education level of women, and government policies.
4. Some of the environmental consequences of human population growth include increased
demands for resources such as food, clean water, and energy. These increased demands result
in greater expansion of settlements and farms into wild lands, deforestation, soil erosion, water
pollution, introduction of pesticides, increased soil salinity, and loss of biodiversity.