populations Flashcards
what determines how pop change in size through time?
- immigration / emigration
- death
- birth rates
3 mechanisms of density dependence?
- competition
- predation
- disease
demography
study of rates of…
- births
- deaths
- immigration
- emigration
and factors that cause them to vary
life tables
- summarises survival & reproductive rates in diff age groups
- based on single cohort
- requires long-term study of pop with marked individs (birds, mammals, plants)
cohort analysis
start with large no. individ at birth (ages between 0 and 1) -> see how long it takes them to die
sessile organisms
cannot move on their own / lack ability for self-locomotion
eg. oysters
population def
group of individ of same species…
- in a given geographical area…
- that is more or less distinct from other groups
suggest why pop studies can sometimes be inaccurate
edge of pop not well defined as hard to judge where one pop ends
-> edge is human determined not geographical
some def for a pop include that individuals in a pop can interbreed, but that is a bit restrictive
-> why?
-> juveniles cannot breed
-> social interaction limitations for some sp
-> some species breed asexually
suggest why density of a pop is better measured by measuring ‘individ per unit area’ not by measuring absolute pop size
- may occupy v large area
- easier to make comparisons between pops
measuring pop density
- count all individ
- count individ in random samples / along a transect
- convert from density of indicators (nests, burrows, fecal droppings, mole hills)
-> as some species are really hard to find (nocturnal, camouflage, rare, etc)
capture-mark-recapture
- capture set of individs
- mark and release them
- capture another set
- % marked individs in 2nd set = % that 1st was of total pop
logistical model
- growth slows down at higher densities (bigger pop size)
- implication: birth-rate, death-rate, migration-rate change with pop density
density of a pop
no. individs per unit area/vol
eg. no. of oak trees per km²
dispersion
pattern of spacing among individs within boundaries of the pop
density dependent examples
- a death rate that ↑ with pop density
- a birth rate that ↓ with ↑ density
density independent factors
- eg. temp & precip.
-> can cause dramatic changes to pop size
mechanisms of density dependence
-
density dependence regulation
influence of pop density on birth rates & death rates
- as pop density ↑…
- resources become more limited
- competition for resources ↑
- factors like predation, disease & intraspecific competition may lead to ↑ death rates or ↓ birth rates
disease in density dependence
- disease transmission
- ↑ density –> more contacts -> ↑ transmission
- e.g. resp diseases (flu & TB)
-> but less so for sexually transmitted diseases
causes of pop fluctuations
- change in abiotic env
- scramble/contest competition
- predator-prey interaction
- disease
- metapops -> group of spatially sep. pops of same sp which interact at some level
-> where suitable habitat occurs in patches in land/sea
