population structure and dynamics

population

a group of coexisting individuals of the same species

have characteristics not possessed by individuals - demographic parameters

characteristics of populations

density, natality (births), mortality, age structure, sex ratios

can use these characteristics to predict growth and shrinking

population growth - logistic growth curve

phase 1 is exponential, unlimited growth - intrinsic rate of increase (r), abundant food, no disease, no predators, no density dependence

2 is transitional growth, limiting factors begin to decline the above growth, density dependence increases

phase 3 is the plateau or carrying capacity (K), no growth bc limited factors (these factors lower or raise K, dynamic)

maybe do the formulas?

exponential population growth

J shaped curve

characteristic of some populations which are rebounding, but not common and cannot be sustained long

occurs in pest species when provided with naive, perfect environment

and non-native species when introduced and has no natural predators or diseases to keep in check

ex european starling

160 released in central park in NY in 1890 to bring something from home to the US

spread to california by 1942, now 100s of millions in north america

carrying capacity and logistic model

at low density, pop growth rate is driven by r, grows rapidly

at high density, pop growth is slower as density effects exert their effect

maximum sustained yield (MSY)

where N is ½ of K, point where the growth curve changes from increasing to decreasing

this is the theoretically sustainable harvest level, population can respond positively

what changes populations

disruptions in the population resulting in outbreaks - density dependent or independent, ex is climate changes and disturbances

those that regulate the population and return it to original density after disturbance, always density dependent ex food, shelter

actual population growth

rate of increase = (births - deaths) - (immigration - emigration)

population regulation

a process where a density dependent factor tends to return a population to its equilibrium, K by altering the birth or death rate

population generally remains within a certain range of sizes which is considered stable

density dependence

related to changes in the proportion of the population dying or being born caused by changes in population density

includes disease, competition, predation, waste accumulation, stress, emigration

density independent

related to changes in the proportion of the population dying or being born unrelated to population size

ex extreme wether such as tornados, hurricanes, heat, flood, drought, cold → stochastic

depensation effect

inverse density dependence

when predators have a destabilizing effect on population size, move population size further from K rather than nearer

considerations in population regulation

commodities - commercial harvest prices, for ex beaver pelts or fisheries, controls the effort and thus potential harvesting of the population

time lags - predator populations may lag behind prey numbers as response, ex lynx hare

overcompensation

erratic appearing population fluctuations occurring from density dependence

occurs when population growth is high, and grows so fast that it overshoot the equilibrium and then has to retreat

factors affecting density dependence

regulation mechanisms, intraspecific competition, disease, foraging arena theory

regulation mechanisms

control population growth via intraspecific competition

predation and resource competition - for food, shelter, nesting sites, and territory

intraspecific competition

individuals of the same species utilize common resources that are in short supply or

competition occurs when the organisms seeking that resource harm one another in the process

tested in food addition experiments

how to determine is food is the cause of regulation

what type of food is eaten, how much food is needed, how much food is available?

what is needed must exceed what is available for competition to occur

hard to measure potential food, and we often likely think more food is available than the species might

foraging arena theory

trophic interactions in aquatic ecosystems occur in spatially (distribution of predators relative to prey) or temporally restricted arenas so interaction rates are limited by the exchange rates of prey in and out of the arenas

causes potential bottlenecks

disease as a regulator

often present in populations at low levels but becomes a major source of mortality at high population densities when populations are stressed, ex stages of malnutrition

ex fish farms and their use of antibiotics to deter disease, attempts to max yield of fish protein