Bio-203 Ch 53; Population Ecology

what does population ecology explore?

how biotic and abiotic factors influence the abundance, dispersion, and age structure of populations

what is a population?

a group of individuals of a single species living in the same general area

populations are described by what?

their boundaries and size

what is density in population ecology?

the number of individuals per unit area or volume

what is dispersion in population ecology?

the pattern of spacing among individuals within the boundaries of the population

what can be used to estimate population size?

small sample, an index of population, or the mark-recapture method

what is the mark-recapture method

- scientists capture, tag, and release a random sample of individuals in a population

- marked individuals are given time to mix back into the population

- scientists capture a second sample of individuals and note how many of them are marked

what is the equation for the mark-recapture method?

N = sn/x

what is immigration

the influx of new individuals from other areas

what is emigration?

the movement of individuals out of a population

what can influence the spacing of individuals in a population?

environmental and social factors

which pattern of dispersion is most common?

clumped, in which individuals aggregate in patches

what influences clumped dispersion?

resource availability, mating behaviors, and group defense against predators

what is uniform dispersion?

individuals are evenly distributed

what can influence uniform dispersion?

social interactions such as territoriality, the defense of a bound space against other individuals

what is random dispersion?

where the position of each individual is independent of other individuals

when does random dispersion occur?

in the absence of strong attraction or replusion among individuals

birth, death, and migration are effected by what?

abiotic and biotic factors

what is a demography?

the study of vital statistics of a population and how they change over time

what is a life table?

an age-specific summary of the surivial and reproductive rates within a population

how are life tables made?

by following the fate of a cohort, a group of individuals of the same age

why are males ignored when studying reproductive species?

because only females produce offspring

what is a surviorship curve?

a graphic way of representing the data in a life table

what are the three classifications of survivorship curves?

- type I; low death rates during early and middle life and an increase in death rates among older age groups

- type II; a constant death rate over the organism’s life span

- type III; high death rates for the young and a lower death rate for survivors

reproductive output for several organisms is measured by what?

the average number of female offspring produced by the females in a age group

age-specific reproductive rates vary considerably based on what?

species

ecologists often study population growth in what?

ideal, unlimited conditions

what do idealized situtions help understand?

the capacity of species to increase and the conditions that may facilitate this growth

if immigration and emigration are ignored, the change in population size equals what?

birth minus death

what is exponential population growth?

population increase under idealized conditions

what is the equation for exponential population growth?

dN/dt = rN

what does r equal in the equation for exponential population growth?

the intrinsic rate of increase

what does exponential population growth result in? (graph shape)

J-shaped curve, where the rate of increase is constant, but the population accumulates more new individuals per unit time where it is larger than when it is small

the J-shaped curve of exponential growth characterizes what?

some rebounding populations

exponential growth cannot be sustained for long in a any population; a more realistic population model limits growth by what?

incorporating carrying capacity

what is carrying capacity?

the maximum population size the environment can support

carrying capacity varies with what?

the abudance of limiting resources

what happens in the logistic population growth model?

the per capita rate of population growth approaches zero as the population size nears carrying capacity

what does the logistic model start with and add?

starts with the exponential model and adds an expression that reduces per capita rate of population growth as N increases

what is the equation for the logistic population growth model?

dN/dt = rN(k-N)/k

when N is small compared to k, what happens?

the term (k-n)/k is close to 1 and the per capita rate of population growth will be close to r

when N is large compared to k, what happens?

the term (k-n)/k is close to 0, and the per capita rate of population growth is small

what happens when N equals k?

the population stops growing

the logistic model of population growth produces what? (shape of graph)

sigmoid (S-shaped) curve; where new individuals are added to the population most rapidly at intermediate population sizes and the population growth rate decreases as N approaches k

what two things can the population do in the logistic model of population growth?

1) some populations overshoot k before settling down to a relatively stable density

2) other populations fluctuate greatly and make it difficult to define k

what does the logistic model produce?

a useful starting point for thinking about how populations grow

conservation biologists can use the model to predict what?

rates of population recovery, estimate sustainable harvest rates, and estimate the size below which populations may become extinct

an organisms life history comprises what?

the traits that affect its schedule of reproduction and survival

life history traits are evolutionary outcomes reflected in what?

the devolpment, physiology, and behavior of an organism

what are the three key components of an organisms life history?

1) the age of first reproduction (maturity)

2) how often the organism reproduces

3) how many offspring are produced per reproductive episode

species that exhibit semelparity

reproduce once and die

species that exhibit iteroparity

produce offspring repeatedly

organisms have finite resources, which leads to what?

trade-offs between survival and reproduction

what influences trade-offs between the number and size of offspring?

selective pressures

what is k-selection?

selection for life history traits that are advantageous at high population densities

what is r-selection?

selection for life history traits that maximize reproductive sucess at low density

there are two important questions about regulation of population growth;

1) what environmental factors stop a population from growing indefinitely?

2) why are some populations fairly stable in size, while others are not?

what happens in density-independent populations?

birth rate and death rate do not change with population density

what happens in density-dependent populations?

birth rates fall and death increase with rising population density

density-dependent birth and death rates are an example of what?

negative feedback that regulates population growth

what factors influence density-dependent birth and death rates?

competition for resources, diseases, predation, territoriality, toxic waste, and intrinsic factors

what factors influence carrying capacity?

- competition for resources

- disease

- predation

- territoriality

- intrinsic factors (physiological)

- toxic waste

what does population dynamics focus on?

the complex interactions between biotic and abiotic factors that cause variation in population size

what happens when a population becomes crowded and resource competition increases?

emigration increases

what are metapopulations?

groups of populations linked by immigration and emigration

an individual’s ability to move between populations depends on what?

genetic makeup

why did the human population begin to grow exponentially around 1650?

- industrial revolution

- better farming practices

- advances in medical care

what is the global population? (number)

8 billion

to maintain population stability, a regional human population can exist in one of two configurations;

1) high birth rates and high death rate

2) low birth rate and low death rate

what is the demographic transition?

the movement from high birth and death rates to low birth and death rates

the demographic transition is associated with what?

an increase in the quality of health care and improved access to education, especially for women

what is an important factor affecting population growth?

age structure

what is age structure?

the relative number of individuals of each age in a population

age structure diagrams can help predict what?

a population’s growth trend

what has reduced life expectancy in some countries?

social upheaval, decaying infrastructure, and disease

population ecologist predict a global population of how many and by when?

8.1 - 10.6 billion by 2050

scientists have based estimates of population growth on what?

logistic growth models, area of habitable land, and food availability

what does the ecological footprint do?

summarizes the aggregate land and water area needed to sustain a person, city, or nation

what can be used to calculate ecological footprint?

energy use

carrying capacity can be limited by what?

food, space, nonrenewable resources, or buildup of waste

unlike other organisms, we can regulate our population growth through what?

social changes