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?