53 Chapter Flashcards
Population ecology explores how biotic and abiotic factors influence the density, distribution, size, and age structure of populations.
True
Population
A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring.
Populations are often described by their boundaries and size (the number of individuals living within those boundaries).
True
Density of a population
The number of individuals per unit area or volume.
Dispersion
The pattern of spacing among individuals within the boundaries of a population.
Mark-recapture method
A sampling technique used to estimate the size of animal populations.
Addition of new individuals occur through…
Birth and immigration
Immigration
The influx of new individuals from other areas.
The factors that remove individuals from a population are…
Death and emigration
Emigration
The movement of individuals out of a population and into other locations.
Patterns of dispersion:
Clumped
Uniform
Random
Clumped dispersion
Individuals are aggregated in patches.
Plants and fungi are often clumped where soil conditions and other environmental factors favor germination and growth.
True
Uniform dispersion
Evenly spaced dispersion
A uniform pattern of dispersion may result from…
Direct interactions between individuals in the population.
Territoriality
A behavior in which an animal defends a bounded physical space against encroachment by other individuals, usually of its own species.
Random dispersion
Unpredictable spacing
-The position of each individual in a population is independent of other individuals.
What are the factors that influence population density and dispersion patterns?
The ecological needs of a species, structure of the environment, and interactions among individuals within the population.
Demography
The study of changes over time in the vital statistics of populations, especially birth rates and death rates.
Life table
An age-specific summary of the survival pattern of a population.
Cohort
A group of individuals of the same age
Survivorship curve
A plot of the number of members that are still alive at each age; one way to represent age-specific mortality.
Survivorship curves can be classified into three general types:
Type I curve
Type II curve
Type III curve
Type I curve
Is a general type of survivorship curve that is flat at the start, reflecting low death rates during early and middle life, and then drops steeply as death rates increase among older age-groups.
-Many larger mammals, including humans, that produce few offspring but provide them with good care exhibit this kind of curve.
Type III curve
A general type of survivorship curves in which the curve drops sharply at the start, reflecting very high death rates for the young, but flattens out as death rates decline for those few individuals that survive the early period of die-off.
-This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long-lived plants, many fishes, and most marine invertebrates.
Type II curve
A general type of survivorship curve in which the curves are intermediate, with a constant death rate over the organism’s life span.
-This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, invertebrates, lizards, and annual plants.
In populations not experiencing immigration or emigration, what are the two key factors determining changes in population size?
Survivorship and reproductive rate.
Demographers who study sexually reproducing species generally ignore the males and concentrate on the females in a population because only females produce offspring. Therefore, demographers view populations in terms of females giving rise to new females. The simplest way to describe the reproductive pattern of a population is to ask how reproductive output varies with the number of females and their ages.
True
Reproductive table
An age-specific summary of the reproductive rates in a population.
The exponential growth model describes population growth in an idealized, unlimited environment.
True
Change in population size =
Births + Immigrants - Deaths - Emigrants
Per capita birth rate
The number of offspring produced per unit time by an average member of the population.
Per capita rate of increase
r = b - m
b is the per capita birth rate and m is the per capita death (mortality) rate
Zero population growth (ZPG)
A period of stability in population size, when additions to the population through births and immigration are balanced by subtractions through deaths and emigration.
Exponential population growth
-Occurs when instantaneous per capita rate of increase (r) is greater than zero and is constant at each instant in time.
Growth of a population in an ideal, unlimited environment, represented by a J-shaped curve when population size is plotted over time.
The J-shaped curve of exponential growth is characteristic of…
Some populations that are introduced into a new environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding.
Carrying capacity (K)
The maximum population size that can be supported by the available resources, symbolized as K.
In the logistic population growth model, the per capita rate of increase approaches zero as the population size nears the carrying capacity.
True
Logistic population growth
Population growth that levels off as population size approaches carrying capacity.
Logistic model equation
dN/dt = r”inst”N[(K-N/K)]
The logistic model of population growth produces a sigmoid (S-shaped) growth curve when N is plotted over time.
Some of the basic assumptions built into the logistic model clearly do not apply to all populations. Explain.
The logistic model assumes that populations adjust instantaneously to growth and approach carrying capacity smoothly. In reality, there is often a delay before the negative effects of an increasing population are realized. If food becomes limiting for a population, for instance, reproduction will decline eventually, but females may use their energy reserves to continue reproducing for a short time.
Two assumptions that the logistic growth model makes:
-Populations adjust instantaneously to growth
- Regardless of population density, each individual added to a population has the same negative effect on population growth rate
Life history
The traits that affect an organism’s schedule of reproduction and survival.
A life history entails three main variables:
When reproduction begins, how often the organism reproduces, and how many offspring are produced per reproductive episode.
Semelparity
Reproduction in which an organism produces all of its offspring in a single event; also called big-band reproduction .
Iteroparity
Reproduction in which adults produce offspring over many years; also called repeated reproduction .
No organism could produce as many offspring as a semelparous species and provision them as well as an interoparous species. There is a trade-off between reproduction and survival.
True
K-selection
Selection for life history traits that are sensitive to population density; also called density-dependent selection.
r-selection
Selection for life-history traits that maximize reproductive success in uncrowded environments; also called density-independent selection.
