Population Ecology Flashcards
How are populations described?
Number, spatial distribution, age/size distribution, dynamics-birth, death, immigration and emigration.
What is density?
Number of individuals per unit area or volume-sampling.
Dispersion
How individuals are spread through space.
Clumped groups
Individuals grouped with space between groups-generally response to patchy distribution of resources or grouping behaviour.
Uniform Groups
Individual’s spaced evenly throughout habitat. Response to even distribution of resources, spacing behaviour.
Random Groups
No pattern of spacing through habitat.
What is a cohort?
Group of individuals of the same age in a population.
What does a life table track?
Tracks changes in a cohort through its collective lifespan. Tabulates numbers dying through each age interval, tabulates age specific chance of dying in each interval. Enables us to plot survivorship curves.
Survivorship Curves
Plots survivorship as function of percentage of lifespan for a cohort.
Type 1 Survivorship Curve
Most individuals survive for most of the maximum lifespan, with heavy mortality towards the end. Small amount of offspring, lots of care for each.
Type 2 Survivorship Curve
Individuals face constant probability of dying through lifespan. “Field of bullets,” model.
Type 3 Survivorship Curve
Young individuals face heavy mortality, after reaching a certain point in lifespan, mortality becomes much lower. Large number of young, small investment in each.
What is the assumption in a model of population growth
Emigration and Immigration are equal.
Parameters of Models of Population Growth
N=Number of individuals in a population. G=Number of new individuals added by reproduction. r=per capita increase (average contribution of new individuals per pre existing individuals-constant). K= max number of individuals that habitat can support (carrying capacity).
Exponential Growth Model
Ideal conditions, no limiting factors, no death. G=rN. Population size is purely a function of number of individuals in a population and per capita increase. Unrealistic, but models what is seen in populations in a new environment or in recovery from rapid decrease.
Logistic Growth Model
Incorporates limiting factors. G=rN((K-N)/K). K will vary according to space, time, circumstances and species. Populations will grow their fastest when population size is intermediate relative to K. As populations increase in size, factors limiting growth will have increasing effects bringing population to a halt.
Density Dependent Factors
Birth rates decreasing/death rates increasing with increasing population size. Causes-intraspecific competition for limiting resource, degradation of environment quality, predation increase.
Density Independent Factors
Mortality produced by factors having nothing to do with population size ex: catastrophic weather.
Life Histories
Combination of reproductive characteristics and life expectancy, characterizing a species or population-produced and maintained by natural selection.
Reproductive Characteristics
Number of offspring per reproductive event, age at first reproduction, length of reproductive lifespan, investment in offspring.
Trade-offs required to fulfill reproductive characteristics
Time, energy and nutrients.
r vs K selected organisms
r= organisms that breed in large numbers. K=organisms that breed in small numbers.
r selected environments
Transient, rich resources, but unpredictable density independent controls. Strongly seasonal. Form basis of trophic pyramids in many ecosystems.
K selected environments
Climax with population of organism generally near carrying capacity-hard time dealing with extreme environment changes.
Life History Evolution
Conspecific guppy populations in Trinidad coexist with either Kilifish or Pike-Cichlids. Growth strategy shifts for guppies depending on which fish they live with. (Kilifish eat small immature guppies-guppies grow quick and mature at larger size vs Pike-Cichlids eat larger, mature guppies, so guppies mature at a smaller size).
Management of wild stocks
Estimate maximum sustained yield, which is the maximum harvest which can be taken periodically from a wild population without causing it to decline.
