Post on 29-Jan-2016
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 yearPJ - Juvenile survival rate during year
- Number juveniles produced per adult per year
Example0.760.586.33/pair
Q. Is this a source or a sink pop’n
What happens when good animals love
poor habitats? edges?
an ecological trap
Sources sinks and population dynamics
Habitat qualityHigh >1 Low <1
Habitat selection
Preferred
Avoided
source
sink
Q. What do individuals do and whathappens to populations
i) At low densityii) 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
Habitat 2 - medium qualityhas 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
Ecological traps and population dynamics
Habitat qualityHigh >1 Low <1 Habitat selection
Preferred
Avoided
source
sink
Q. What happens to individuals and populations in the modified environment
i) At low densityii) At high density
source
trap
Ecological traps and population dynamics
Prior to modificationA better quality than B…. Expected breeding success in terr n___ Mean breeding success of population
After modificationA worse than B but A preferredOpen circles - expected successLower 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
Nest
s/ha
Preference Fitness Payoff
Q. Any concerns about the conclusion? Flaspohler et al 2001
Distance to edge (m)
Ecological traps: how good is the evidence?
Habitat edges - Insects
Mantid (Stagmomantis limbata)
Egg case
Ecological traps: how good is the evidence?
Habitat edges - Mantids
Preference Payoff
Egg
case
densi
ty /
ha
Pre
dati
on r
ate
Ries and Fagan 2003 Ecol Appl 28 567-572
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 scaleslandscape, 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 preferredHabitat is a sink
need to distinguish from pseudosinkhabitat with low productivity /survival due to high densities
Sources and sinks - scaling up to populations
Pika Age structured population Juv 1 2 3Two habitats Meadow and Snowbed
Sources and sinks - scaling up to populations
Pika Age structured population Juv 1 2 3Two habitats Meadow and Snowbed
Birth Juv Adult Meadow 1.72 0.3 0.43 0.89Snowbed 0.33 0.21 0.17 0.12
Nt+1/Nt
Meadowsnowbed
Immigration - 3x more immigrants in snowbeds than meadow
Sources and sinks - scaling up to landscapes
DDT caused pop’n crashes in the 50’sManagement strategies
banning of DDT and reintroductions
Sources and sinks - scaling up to landscapes
Post DDTNorthern pop’n - > 1Coastal 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
Lloyd et al 2005 Ecol Applic 15: 1504-1514
Source sink model andBreeding bird survey data
suggest
Ovenbird pop’ns are growing
Wood thrush pop’ns are declining
Summing up
Habitats vary in qualitySource habitats produce an excess of individualsThese individuals can disperse toSink habitats where productivity is less than mortalityDemographic 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 qualityhow will changes in overall population size affect source and sink populations?