Population Growth cont. Flashcards
(25 cards)
Logistic population growth models
incorporate carrying capacity, such that population growth approaches zero as population size nears K; regulated by density dependent factors and falls into two general reproductive strategies; more realistic model and produces an S-shaped population size curve
Carrying capacity (K)
maximum population size the environment can support; varies over space and time w/ abundance of limiting resources
limiting factors include: energy shelter, refuge from predators, nutrient availability, water, and suitable nesting sites
During the logistic population growth, the number of individuals added to the population _____
increases then decreases
When are new individuals added most rapidly?
at intermediate population size, when the breeding population is substantial and resources are abundant; population growth rate decreases as N approaches K
Density independent
birth rate and death rate do not change w/ population density
Density dependent
birth rates and death rates are directly or indirectly regulated by population density; population size can only be regulated by density-dependent factors
Density dependent factors
predation, competition for resources, disease, intrinsic factors, territoriality, toxic waste
Predation
can be density dependent if prey are easier to catch at high density; Ex: kelp populations’ death rate increased as hiding spaces from predators became scarce at high densities
Competition
in crowded populations, increasing population density intensifies competition for resources and reduces birth rates; Ex: farmers reduce competition by applying fertilizers to reduce nutrient limitations on crop yield
Disease
can regulate population density if its transmission rates increase as population becomes more crowded; Ex; influenza and tuberculosis spreads faster in densely crowded cities compared to rural areas
Territoriality
can limit population density when space becomes the resource for which individuals compete; Ex: Cheetahs use chemical markers in urine to warn other cheetahs of their territorial boundaries
Intrinsic factors
physiological factors appear to regulate population size; Ex: hormonal changes in white-footed mice delay sexual maturation and depress immune system at high density making birth rates drop even when food and shelter are abundant
Toxic wastes
accumulation of toxic wastes at high population density can contribute to density dependent regulation of population size; Ex: concentration of ethanol produced by brewer’s yeast becomes toxic at high population density
Which is more common, negative density dependence or positive density dependence?
Negative density dependence
Population dynamics
focuses on the complex interactions between biotic and abiotic factors that cause variation in population size
Example of a large mammal’s population size fluctuating at unpredictable intervals.
Two major population increases and collapses in the moose population on Isle Royale during the last 50 years; 1st collapse due to increase in wolf population, 2nd collapse due to harsh winter conditions
Example of population fluctuating at regular boom and bust cycles.
Snowshoe hares and lynx both follow roughly 10 year population cycles in the forests of northern Cananda and Alaska; overexploitation by predators is an essential factor affecting snowshoe hare cycles; lynx increase and decrease in response to the availability of their prey species
Life history
comprises traits that affect an organism’s schedule of reproduction and survival
What are the five key components that make up life history?
- age/size at reproductive maturity
- allocation of energy to reproduce
- # and size of reproduction
- # of reproductive events
- life span
What are the two reproductive events called?
Iteroparity and Semelparity
Iteroparity
repeated reproductive events throughout a lifetime
Semelparity
a “one-shot” pattern of big-bang reproduction
r-selection
selection for life history traits that maximize reproductive success at low density
K-selection
selection for life history traits that are advantageous at high population densities
