Transcript 1091-Lec9Edge

Summary of lecture 8
Habitat loss -----> fragmentation
an increase in patch
number
a decrease in patch size
increasing patch isolation
higher edge:core ratios
Fragmentation 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 process
Rosenberg 1999
Tanagers - a continental approach
1057 sites
measured
Forest cover
Patch size
Isolation
Edge
Point counts assessed
Tanager
Cowbird
avian predators
other predators
Probability of occurrence
Geographic area.
Scarlet ___
Summer ……
Western -----
Q. Which species would you
expect to be most impacted by
fragmentation?
Low… Fragmentation gradient …high
Probability of occurrence
PC1 - forest cover/patch size/isolation
Low… Fragmentation gradient …high
Q. What do you conclude about fragmentation effects on
tanagers
Biotic processes at edges
Predation - additional factors
Host abundance
Proportion of
nests
depredated
Amount of forest remaining
<15%
45-55%
>90%
Conclusion: The landscape surrounding the patch
influences predation effects at edges
Donovan 1997 Ecology 78 2064-75
Biotic processes at edges
Parasitism - additional factors
0.4
0
0
20
40
60
80
% forest cover
% nests parasitized
0.8
100
80
60
40
20
0
0
20
40
60
80
% forest cover
100
Conclusion: The landscape surrounding the patch
influences cowbird abundance and parasitism rates
Thompson et al. 2000
Daily mortality rate
Edge effects on predation and parasitism in
Eastern and Western Landscapes
0.06
Fragmented
Unfragmented
0.04
0.02
0
East
West
Data: 656, 1122, 1533 1463 nests 23 species
Cavitt and Martin 2002 Studies in Avian Biol 25
Edge effects on predation and parasitism
in Eastern and Western Landscapes
0.4
Fragmented
unfragmented
Proportion of nests
parasitized
0.3
0.2
0.1
0
East
West
Data: >10000 nests 23 species
Cavitt and Martin 2002 Studies in Avian Biol 25
Biotic processes at edges
Predation at edges
64 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/isolation
quality
EXAMPLES
Forestry - determining best practises
Group retention harvesting
50% retained
30% retained
10 % retained
How do we assess how to cut up the block
or the quality of the patches that are left ??
Protecting kit foxes in California
8 sites
Sites vary
How 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/isolation
quality
Q. How would you assess quality or decide
what patches to protect?
One approach we could protect preferred habitat
Preference is often evaluated based on
usage relative to availability
high usage habitat is preferred
low usage is avoided
Density
Presence/Absence
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)
Eg1 White footed mice
Eg2 Spanish Imperial Eagle
Prefer forest over edge
Prefer cork oak/stone pine
over marsh and coastal dunes
Preference has a fitness pay-off
Survival rate is higher
Morris 1996 Oikos 75:207-219
Preference has a fitness payoff
Breeding success is greater
Ferrer and Donozar 1996 Ecology 77
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
populations
Source
areas where local reproductive success is
greater than mortality
Sink
areas where local productivity is less than local
mortality
Source or sink
Simplest case - one patch
Finite rate of pop’n growth,  = PA+PJ
Example
0.76
PA - Adult survival during year
0.58
PJ - Juvenile survival rate during year
 - Number juveniles produced per adult per year6.33/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 clownfish
Imprint to chemical cues
in the nest
Use these cues to find
host anemones
Peregrine falcon
Ind’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
plant chemistry
Dippers assess
invertebrate abundance
How do animals assess habitat suitability?
- the use of cues that predict habitat quality
Periodical cicada
Females use canopy openness to
select where they lay eggs.
Canopy openness predicts
long term tree growth
rapid root development and
the 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 year
Older 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 effects
Discuss why edge effects vary
Collect data to evaluate patch quality
Understand any assumptions made when using
this data
Be able to distinguish between a source and a
sink population
NEXT – bad decisions