Extinction & Recovery

Question 1

species extinction rates

Answer 1

100-1000x higher than the background rate

Question 2

population extinction rate

Answer 2

10-100x greater than species extinction rate

Question 3

what is a population?

Answer 3

a group of interbreeding individuals of the same species inhabiting the same area

Question 4

source population

Answer 4

where local reproduction exceeds mortality and there is a net emmigration of individuals

Question 5

sink population

Answer 5

local reproduction is insufficient to balance mortality and numbers are maintained by immigration

Question 6

extirpation

Answer 6

loss of a single population when the last individual dies in a specific region

Question 7

global variation in population decline

Answer 7

mean species abundance
- most affected areas are where crops are grown, cities, changes to natural envr., high climate change or other drivers

Question 8

what if there is no historical baseline in abundance studies?

Answer 8

model past, use rates from the fossil record, reference population in ‘pristine’ state, in absence of human activites

Question 9

Dickcissel examples

Answer 9

population map over time
- highly dynamic ( immigration, emigration, local extinction… ) = all part of normal species range

Question 10

trends in population size maps

Answer 10

-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

Question 11

Conservation : declining populations

Answer 11

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

Question 12

conservation: small populations

Answer 12

interested more in recovery, and proximate causes or random causes
- demographic
-environmental
- catastrophes

Question 13

extinction vortex = positive feedback loop

Answer 13

causal factors lead small populations to become increasingly more vulnerable as they spiral toward extinction
- interactions of proximate and ultimate factors

Question 14

positive distribution - abundance relationship

Answer 14

relationship between the number of sites as species occupies and the average density of individuals in occupied sites

Question 15

distribution - abundance example
North American BIRDS

Answer 15

-larger spatial range, and larger distribution species tend to be more abundant
-smaller species range = small abundance

Question 16

why does the relationship between distribution and abundance matter for extinction?

Answer 16

• 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

Question 17

anthropogenic impacts on the distribution- abundance relationship

Answer 17

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

Question 18

Pe

Answer 18

probability of extinction

Question 19

Pn = (1-Pe)^n
where n = years
Pe is probability of extinction

Answer 19

Pn is the probability of persistence

Question 20

Probability of regional persistence
- independent of one another
- x is the number of populations

Answer 20

Px = 1(Pe)^x

Question 21

population size
-Nt (current size)

Answer 21

N(t+1) = Nt +(b) irths + (i)mmigrants - (d)eath - (e)migrants

Question 22

simplest equation for population growth

Answer 22

N(t+1) = lamda x Nt
- lamda is rate of increase

Question 23

when does geometric growth occur?

Answer 23

lamda > 1.0
- population is not limited by resources, habitat, mates etc.

Question 24

environmental stochasticity

Answer 24

variation in population size caused by variation through time in growth (lamda) due to variation in weather/ climate
e.g.catastrophes ( hurricanes)

Question 25

demographic stochasticity

Answer 25

variation in population size caused by random variation among individuals in their reproductive activity, even if the environment is unchanging

Question 26

why does demographic stochasticity occur?

Answer 26

births and deaths are discrete random events that occur sequentially