Population Ecology

why understand populations?

invasion ecology, conservation biology, disease ecology, restoration ecology

population density

number of individuals per unit area

can be absolute, or ecological

changes in response to food supply (functional response curves), and numerical response

ecological density

number of individuals per unit area of a suitable habitat

ex number of moose per ha of forest

numerical response

change in predator population density in response to changes in prey density

drivers are reproduction and dispersal

in relation to functional curves which are change in feeding rate

reproduction numerical response

time lag between peak prey population and peak predator population

predators need time to produce offspring, ex lynx and hares

non-synchronized predator prey dynamics

dispersal numerical responses

aggregative response

no time lag between the peak of predator and prey populations

predators are highly mobile and track prey across space, ex birds of prey

synchronized predator prey dynamics

case study birds of prey numerical responses

predator and prey population densities track each other closely with no time lag

dispersal of kestrels and owls into areas with voles is what is driving the changes in densities

population distribution

geographic distribution of a species, limited by the physical environment (both abiotic and biotic conditions) and species niche requirements

distribution patterns

small scale individuals will have randomly, regularly, or clumped distributions

small scale depends on the species and can be km or m or smaller

random distribution

small scale

neutral interactions among individuals of a species, individuals have equal prob of appearing anywhere in an area

random disturbances, uniform distribution of resources

ex dandelions

regular distribution

small scale

antagonistic interactions among individuals of same species, uniform distribution of resources and uniform depletion

ex red winged black bird

clumped distributions

small scale

mutual interactions and attractions

patchy resources, and dispersal limitations can reinforce

ex herds of elk

large scale distributions

individuals are clumped in hot spots, some species have a more restricted range and so are more localized in areas

why are some species limited in distribution

all organisms have limited resources and energy, it takes these resources to survive and reproduce and so being on the edge of their niche requirements is costly

evolution has helped aid species to survive in one specific area

dispersal

permanent movement of individuals usually from one population to another - increases range

distinct from migration due to permanence

immigration or emigration

seed dispersal adaptations

gravity, ballistic, wind - samara, ants/insects, water - coconuts, animals - burs or berries

range expansion and climate change

ex tree dispersal and range expansion following the pleistocene

different species (w different seeds) dispersed back north, speed and colonization depended on range of tolerance and niche size (and dispersal abilities)

ex range expansion and killer bees

africanized bees are an aggressive hybrid which began in brazil in order to survive in warm temp and produce lots of honey

but large swarms escaped and were able to find new colony locations, started spreading north into USA

temperature limited spread, as with mating with less aggressive species - but climate change may allow further north expanision

metapopulations

made up of groups of subpopulations living in patches of habitat connected by an exchange of individuals

only exist when dispersal is possible

specific habitat requirements

ex metapopulations and rocky mountain butterfly

specific habitat requirement is host plant lanceleaf stonecrop which has patchy distribution

population size is correlated with meadow size, individuals emigrate between

but fire suppression, climate change (forest encroachment) can change host plant potentially changing butterfly density

rarity

species rarity and commonness is influenced by geographic range - extreme or restricted

habitat tolerance - broad or narrow

local pop. size - large or small

combinations of these aspects determine rarity

common species

will have large geographic range, broad habitat tolerance, and large local population

ex dandelion and house sparrow

slightly rare species

only one or two aspects of rarity which slowly increases vulnerability

• can be either small pop, restricted range, or narrow tolerance

FOR EX narrow habitat tolerance but large range and large population

rare species

three aspects of rarity, way more prone to extinction

will have restricted geographic range, narrow habitat tolerance, and small local population

ex gorilla

SARA

species at risk act, Canadian categorization

ranks species from extinct until not at risk