Summary of lecture 8

Habitat loss -----> fragmentation an increase in patch

number a decrease in patch size increasing patch

isolation higher edge:core ratiosFragmentation can have -ve and +ve

effects

The relative importance of habitat loss and habitat configuration can be assessed using statistical models

Outline for Lectures 9 and 10

Edge effects - revisited

Assessing patch quality in a fragmented landscape

Source vs sink populations

Ecological traps

Scaling up and predicting population dynamics

Fragmentation - understanding the processRosenberg 1999Tanagers - a continental approach

1057 sites measured Forest cover Patch size Isolation Edge

Point counts assessed

Tanager Cowbird avian predators other predators

Pro

bab

ility

of

occ

urr

en

ceGeographic area. Scarlet ___Summer ……Western -----

Low… Fragmentation gradient …high

Q. Which species would you expect to be most impacted

by fragmentation?

PC1 - forest cover/patch size/isolationPro

bab

ility

of

occ

urr

en

ce

Low… Fragmentation gradient …high

Q. What do you conclude about fragmentation

effects on tanagers

Biotic processes at edgesPredation - additional factors

Conclusion: The landscape surrounding the patch influences predation effects at edges

Host abundance

Proportion of nests depredated

Amount of forest remaining <15% 45-55% >90%

Donovan 1997 Ecology 78 2064-75

Biotic processes at edgesParasitism - additional factors

Conclusion: The landscape surrounding the patch influences cowbird abundance and parasitism rates

0 20 40 60 80 100 % forest cover

0 20 40 60 80 100 % forest cover

Cow

bir

ds

per

poin

t co

un

t

% n

est

s p

ara

siti

zed 80

60

40

20

0

0.8

0.4

0

Thompson et al. 2000

Edge effects on predation and parasitism in Eastern and Western Landscapes

Data: 656, 1122, 1533 1463 nests 23 species Cavitt and Martin 2002 Studies in Avian Biol

25

East West

0.06

0.04

0.02

0Daily

mort

alit

y

rate

FragmentedUnfragmented

Edge effects on predation and parasitism in Eastern and Western Landscapes

Data: >10000 nests 23 species Cavitt and Martin 2002 Studies in Avian Biol 25

East West

0.4

0.3

0.2

0.1

0

Pro

port

ion

of

nest

s p

ara

siti

zed

Fragmentedunfragmented

Biotic processes at edges

Predation at edges64 experiments later

Overall - edges have a significant effect

But

N America > Central America

Deciduous forest > coniferous forest = tropical forest

Effect varies with habitat in matrix

Question for discussion

Why does fragmentation have different effects on predation and parasitism rates east and west of the Rockies?

Habitat loss ---> fragmentation ---> patches that vary in

size/shape/isolationquality

EXAMPLES

Forestry - determining best practises

Group retention harvesting50% retained30% retained10 % retained

How do we assess how to cut up the blockor the quality of the patches that are left ??

Protecting kit foxes in California

8 sites

Sites varyHow do we assess which to protect first?

Protecting murrelet breeding habitat

BC - >130 WHA’s have been established for murrelets

Forest habitat in Desolation Sound(green) Nests (red)

How do we decide what forest patches to protect?

Habitat loss ---> fragmentation ---> patches that vary in

size/shape/isolationquality

Q. How would you assess quality or decide what patches to protect?

One approach - we could protect preferred habitat

Density

Presence/Absence

Preference is often evaluated based on usage relative to availabilityhigh usage habitat is preferredlow usage is avoided

Use of density or presence/absence to assess habitat quality or decide what patches to protect assumes

animals are ideal (have perfect knowledge)animals are free (not constrained)

Morris 1996 Oikos 75:207-219

Eg1 White footed mice

Prefer forest over edge

Preference has a fitness pay-offSurvival rate is higher

Eg2 Spanish Imperial Eagle

Ferrer and Donozar 1996 Ecology 77

Prefer cork oak/stone pine over marsh and coastal dunes

Preference has a fitness payoff Breeding success is greater

Use of density or presence/absence to assess habitat quality or decide what patches to protect assumes

animals are ideal (have perfect knowledge)animals are free (not constrained)

so density is correlated with rs and survival and

preferred habitats can support source populationsSourceareas where local reproductive success is greater than mortalitySinkareas where local productivity is less than local mortality

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

How do animals assess habitat suitability?

Internal information - habitat imprinting

Direct habitat assessment

Indirect habitat assessment

- presence of conspecifics (“social attraction”)

- performance of conspecifics - (“public information”)

- use of cues that predict quality

How do animals assess habitat suitability?

- habitat imprinting

False clownfishImprint to chemical cues in the nestUse these cues to find host anemones

Peregrine falconInd’s that fledge from buildings are more likely to breed on builings than cliffs and vice versa

How do animals assess habitat suitability?

- direct habitat assessment

Koalas assess Dippers assessplant chemistry invertebrate abundance

How do animals assess habitat suitability?

- the use of cues that predict habitat quality

Periodical cicadaFemales use canopy openness to select where they lay eggs.

Canopy openness predictslong term tree growthrapid root development andthe food supply for the developing nymphs

How do animals assess habitat suitability?

- Presence of conspecifics (“social attraction”)

From polychaetes

to birds

How do animals assess habitat suitability?

- Performance of conspecifics (“public information”)

First time breeders select sea cliffs based on their productivity in the previous yearOlder breeders emigrate from the least productive cliffs and settle at the most productive (Danchin et al

1998)

You should be able to

Design an experiment to test for edge effectsDiscuss why edge effects vary

Collect data to evaluate patch qualityUnderstand any assumptions made when using this data

Be able to distinguish between a source and a sink population

NEXT – bad decisions