1. 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

2. 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

3. Simplest case - one patch Finite rate of pop’n growth,  = PA+PJ
Source or sink
Simplest case - one patch
Finite rate of pop’n growth,  = PA+PJ
Example
0.76
0.58
6.33/pair
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

4. What happens when good animals love
poor habitats? edges?
 an ecological trap

5. Sources sinks and population dynamics
Habitat quality
High  >1 Low  <1
Habitat selection
Preferred
Avoided
source
sink
What do individuals do and what
happens to populations
At low density
At high density

6. 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

7. Ecological traps Habitat 1 - HIGH quality has attributes ABC
Habitat 2 - medium quality
has attributes CDE but not AB
Natural selection leads to
preference for habitat with AB
Habitat 1MODIFIED---> LOW quality
still has attributes ABC
Habitat 2 - medium quality
has attributes CDE but not AB
Preference based on cues AB is maladaptive
- Suitable but avoided

8. Ecological traps and population dynamics
Habitat quality
High  >1 Low  <1
Habitat selection
Preferred
Avoided
source
trap
source
sink
What happens to individuals and populations in the modified environment
At low density
At high density

9. 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:

10. 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

11. Ecological traps: how good is the evidence?
Habitat edges - Birds
Preference Fitness Payoff
Nests/ha
Distance to edge (m)
Q. Any concerns about the conclusion?
Flaspohler et al 2001

12. Ecological traps: how good is the evidence?
Habitat edges - Insects
Arizona
Egg case
Mantid (Stagmomantis limbata)

13. Ecological traps: how good is the evidence?
Habitat edges - Mantids
Preference
Payoff
Egg case density /ha
Predation rate
Ries and Fagan 2003 Ecol Appl

14. Ecological traps: how good is the evidence?
Exotic species
Lonicera spp
Bush honeysuckles

15. Ecological traps: how good is the evidence?
Exotic species
Preference
Payoff

16. 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

17. 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

18. Sources and sinks - scaling up to populations
Pika Age structured population Juv
Two habitats Meadow and Snowbed

19. Sources and sinks - scaling up to populations
Pika Age structured population Juv
Two habitats Meadow and Snowbed
Birth Juv Adult 
Meadow
Snowbed
Nt+1/Nt
Meadow
snowbed
Immigration - 3x more immigrants in snowbeds than meadow

20. Sources and sinks - scaling up to landscapes
DDT caused pop’n crashes in the 50’s
Management strategies
banning of DDT and reintroductions

21. 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

22. Sources and sinks - scaling up to landscapes
DATA - 30 BBIRD sites 17 states 22 spp
- National Landcover Dataset 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

23. Breeding bird survey data suggest
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:

24. 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

25. 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?