Extinction & Recovery Flashcards
species extinction rates
100-1000x higher than the background rate
population extinction rate
10-100x greater than species extinction rate
what is a population?
a group of interbreeding individuals of the same species inhabiting the same area
source population
where local reproduction exceeds mortality and there is a net emmigration of individuals
sink population
local reproduction is insufficient to balance mortality and numbers are maintained by immigration
extirpation
loss of a single population when the last individual dies in a specific region
global variation in population decline
mean species abundance
- most affected areas are where crops are grown, cities, changes to natural envr., high climate change or other drivers
what if there is no historical baseline in abundance studies?
model past, use rates from the fossil record, reference population in ‘pristine’ state, in absence of human activites
Dickcissel examples
population map over time
- highly dynamic ( immigration, emigration, local extinction… ) = all part of normal species range
trends in population size maps
-low density population on the margin of species range
-core population is much more dense and abundant
-expectation is to collapse from outside or shrink
Conservation : declining populations
ultimate causes (often human related), interactions amongst all causes (complex) = populations can’t adapt to multiple drivers at once
-elevated & persistent mortality
-habitat destruction /fragmentation
-harvesting
-pollution
-environmental change e.g. climate
conservation: small populations
interested more in recovery, and proximate causes or random causes
- demographic
-environmental
- catastrophes
extinction vortex = positive feedback loop
causal factors lead small populations to become increasingly more vulnerable as they spiral toward extinction
- interactions of proximate and ultimate factors
positive distribution - abundance relationship
relationship between the number of sites as species occupies and the average density of individuals in occupied sites
distribution - abundance example
North American BIRDS
-larger spatial range, and larger distribution species tend to be more abundant
-smaller species range = small abundance
why does the relationship between distribution and abundance matter for extinction?
- may change because of human disturbance
- small range, small abundance = double jeopardy
-rare + locally restricted would be most at risk - with time, driver range down = pop. size will decline too
anthropogenic impacts on the distribution- abundance relationship
ex: moss carpets and arthropods
- habitat destruction drives extinction in species with low numbers and occupancy
-habitat loss ( ultimate) drives species down, constrained to fragments, species can’t maintain range
range and population size must be managed
Pe
probability of extinction
Pn = (1-Pe)^n
where n = years
Pe is probability of extinction
Pn is the probability of persistence
Probability of regional persistence
- independent of one another
- x is the number of populations
Px = 1(Pe)^x
population size
-Nt (current size)
N(t+1) = Nt +(b) irths + (i)mmigrants - (d)eath - (e)migrants
simplest equation for population growth
N(t+1) = lamda x Nt
- lamda is rate of increase
when does geometric growth occur?
lamda > 1.0
- population is not limited by resources, habitat, mates etc.
environmental stochasticity
variation in population size caused by variation through time in growth (lamda) due to variation in weather/ climate
e.g.catastrophes ( hurricanes)
demographic stochasticity
variation in population size caused by random variation among individuals in their reproductive activity, even if the environment is unchanging
why does demographic stochasticity occur?
births and deaths are discrete random events that occur sequentially
