Download 1091-Lec10(TrapA)

Outline for Lectures 9 and 10
Edge effects
Assessing patch quality in a fragmented
landscape
Source vs sink populations
Ecological traps
Scaling up and predicting population
dynamics
Habitat Quality
Source (good habitat)
areas where local reproductive success is
greater than mortality
 >1
Sink (poor habitat)
areas where local productivity is less than local
mortality
 <1
Source or sink
Simplest case - one patch
Finite rate of pop’n growth,  = PA+PJ
PA - Adult survival during year
PJ - Juvenile survival rate during year
 - Number juveniles produced per adult per year
Q. Is this a source or a sink pop’n
Example
0.76
0.58
6.33/pair
What happens when good animals love
poor habitats?
edges?
 an ecological trap
Sources sinks and population dynamics
Habitat selection
Preferred
Avoided
Habitat quality
High  >1 Low  <1
source
sink
Q. What do individuals do and what
happens to populations
i) At low density
ii) At high density
BUT
Animals can be fooled
Mayflies are attracted to horizontally polarized light
Because light
reflected from a
water surface is
polarized
But so is light reflecting off tarmac
So mayflies frequently lay eggs on asphalt
Ecological traps
Habitat 1 - HIGH quality has attributes ABC
Natural selection leads to
preference for habitat with AB
Habitat 2 - medium quality
has attributes CDE but not AB
Habitat 1MODIFIED---> LOW quality
still has attributes ABC
Preference based on cues AB is maladaptive
Habitat 2 - medium quality
has attributes CDE but not AB
- Suitable but avoided
Ecological traps and population dynamics
Habitat selection
Habitat quality
High  >1 Low  <1
Preferred
source
trap
Avoided
source
sink
Q. What happens to individuals and populations
in the modified environment
i) At low density
ii) At high density
Ecological traps and population dynamics
Prior to modification
A better quality than B
…. Expected breeding success in terr n
___ Mean breeding success of population
After modification
A worse than B but A preferred
Open circles - expected success
Lower line - mean breeding success
Kokko and Sutherland 2001 Evol Ecol Research 3: 537-551
Ecological traps and population dynamics
Kokko and Sutherland model shows
both reduced reproduction or mortality
can cause traps
initial population size is important in
determining the outcome
there is a threshold level of trap
habitat that will result in pop’n
extinctions
Ecological traps: how good is the evidence?
Habitat edges - Birds
Fitness Payoff
Nests/ha
Preference
Distance to edge (m)
Q. Any concerns about the conclusion?
Flaspohler et al 2001
Ecological traps: how good is the evidence?
Habitat edges - Insects
Egg case
Mantid (Stagmomantis limbata)
Ecological traps: how good is the evidence?
Habitat edges - Mantids
Ries and Fagan 2003 Ecol Appl 28 567-572
Payoff
Predation rate
Egg case density /ha
Preference
Ecological traps: how good is the evidence?
Exotic species
Lonicera spp
Bush honeysuckles
Ecological traps: how good is the evidence?
Exotic species
Preference
Payoff
Conclusion
Traps are created
by diverse processes
in many habitat types
across a diversity of spatial scales
landscape, within patches,
within territiries (eg selecting nest sites)
SO potential impact is ENORMOUS
But identifying ecological traps is
DIFFICULT AND DATA INTENSIVE
need to show
Habitat is preferred
Habitat is a sink
need to distinguish from pseudosink
habitat with low productivity /survival
due to high densities
Sources and sinks - scaling up to populations
Pika Age structured population Juv 1 2 3
Two habitats Meadow and Snowbed
Sources and sinks - scaling up to populations
Pika Age structured population Juv 1 2 3
Two habitats Meadow and Snowbed
Meadow
Snowbed
Nt+1/Nt
Birth
1.72
0.33
Juv
0.3
0.21 0.17
Adult
0.43
0.12

0.89
Meadow
snowbed
Immigration - 3x more immigrants in snowbeds than meadow
Sources and sinks - scaling up to landscapes
DDT caused pop’n crashes in the 50’s
Management strategies
banning of DDT and reintroductions
Sources and sinks - scaling up to landscapes
Post DDT
Northern pop’n -  > 1
Coastal pop’n -  < 1
Wootton and Bell 1992
Source-sink dynamics should lead to recovery
With
captive
release
Without
Sources and sinks - scaling up to landscapes
DATA - 30 BBIRD sites 17 states 22 spp
- National Landcover Dataset - 21 types
Nest parasitism - increases with the amount of developed
land within a 20 km radius
Predation - edge effect in East
- increases with amount of developed land
within a 10 km radius
Combined ---> landscape effect
- productivity decreases with amount of developed
land within 10 km radius
NEXT STEP - link landscape effects to 
- based on  = PA+PJ
-  declines with amount of developed land
Source sink model and
Breeding bird survey data
suggest
Ovenbird pop’ns are growing
Wood thrush pop’ns are declining
Lloyd et al 2005 Ecol Applic 15: 1504-1514
Summing up
Habitats vary in quality
Source habitats produce an excess of individuals
These individuals can disperse to
Sink habitats where productivity is less than
mortality
Demographic rates can vary temporally
Source-sink dynamics have implications for
identifying critical habitat
Questions you should be able to discuss.
What are the issues about using
presence/absence/abundance data to
identify critical habitat?
What data is needed to determine
whether a habitat acts as a source or a
sink?
If animals can evaluate habitat quality
how will changes in overall population
size affect source and sink populations?