Summary of lecture 8 Habitat loss -----> fragmentation an increase in patch number a decrease in...
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Transcript of Summary of lecture 8 Habitat loss -----> fragmentation an increase in patch number a decrease in...
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