Transcript 1091-Lec8Fraga

Outline for the next 2 weeks
Habitat loss, degradation and fragmentation
changes to the landscape
evaluating the impacts
Guest – Species at Risk –Steph Hazlitt (BC)
Guest – Conservation – a Mexican perspective
Edge effects
Ecological Traps
Guest – Species at Risk – Dave Toews (Fed.)
SOME TERMINOLOGY
Habitat loss - major change to habitat
- all spp adversely affected
- timespan for recovery v long
Habitat degradation - change that affects
many but not all species
- may be temporary
Habitat transformation/conversion
- refers to process of change
How important is habitat loss?
Habitat loss is the biggest threat to
terrestrial threatened species
Fig 3.6 text
How much habitat has been lost?
DATA: Millenium ecosystem assessment
Fig. 6.1 text
How much habitat has been lost?
AQUATIC SYSTEMS
Coral reefs:20% LOST + 20% DEGRADED
Mangroves: 35% of assessed systems destroyed in last
20yrs
Freshwater: 3-6 X more is stored behind dams and in
reservoirs than flows in the world’s rivers
DATA: Millenium ecosystem assessment
Coral Reef – Degradation
CO2
Currently
380ppm - 80 higher than any time in last 420,000 yrs
Predicted
500 ppm by end of century
---> global temperature increase of 2C
Response
Reef-building coral will be pushed close to their
thermal limit
Carbonate levels will drop below those to sustain coral
reef accretion
Increased bleaching/disease/mortality
Huegh-Guldberg et al. 2007 Science 318:1737-1742
Major causes of habitat loss and degradation
Agriculture (conversion to crops, livestock)
Extraction (mining, fisheries,forestry)
Development
DATA: Birdlife International
Fig 6.9 text
Habitat loss: agriculture
Grasslands, savannas and shrublands
-cover 40.5% of earth’s surface
-ideal for agriculture and livestock
Dark areas - >30% landscape is cultivated
Habitat loss: deforestation
Forests
Global
- 50% of pre-agricultural cover lost in 300 yrs
Tropical
- 1990’s Africa lost 8% of its forested area
-current loss 100,000 km2 per year
Canada - 10,000 km2 per year
Habitat loss and habitat fragmentation
Fragmentation (process) has two components:
1) reduction in habitat amount
2) change in habitat configuration
increase in number of patches
decrease in size of patches
increase in isolation
Habitat loss with
different effects
on
Number of patches
Mean patch size
Mean isolation
DOES IT MATTER?
Patch number and size also changes
the ratio of edge:core habitat
core
CORE
EDGE
Edge habitat increases with fragmentation
Number of patches
% deformation
matrix
habitat
Habitat loss
Habitat loss +
fragmentation
Number patches
Mean patch size
Mean isolation
Habitat loss +
fragmentation+
change in habitat
quality at edge
Theoretical effects of habitat loss
Eg Jansson and Angelstam 1999
Theoretical effects of fragmentation per se
+ve landscape complementarity
via access to multiple resources
stability of single species dynamics
via asynchronous disturbances
stability of 2-competitor systems
via trade-off in competitive and dispersal ability
temporary refugia
-ve patch size and resource limitation
edge effects
What approaches can be taken to
disentangle the effects of
habitat loss and
fragmentation
ie changes in habitat configuration
Statistical methods to assess effects
Residuals - unexplained variation after
controlling for change in patch size or
total edge due to loss of habitat
Statistical methods to assess effects
Eg Villard et al 1999
3 regions in Ontario
33 landscapes (2.5kmx2.5km)
Measured
% forest cover
total length of edge
mean distance to next patch
presence/absence 15 bird spp
Statistical methods to assess effects
Cover - 6 spp
Edge - 4 spp Isolation 1 spp
MESSAGE OF PAPER
Both cover and configuration predict presence
Responses are species specific
Effects were not characterized by thresholds
Habitat Loss Fragmentation - what is happening
core
CORE
EDGE
Fragmentation: understanding the process
Edge habitat will be impacted by biotic factors
resource availability will change
within patch
and
outside patches
species interactions will change
predation/herbivory/parasitism
Edge habitat is also modified by:
abiotic factors
(wind, water fluxes, solar radiation)
---> change in vegetation structure
microclimate
ground cover
Eg pacific northwest
tree mortality and blowdown is higher
humidity is reduced
physical effects extend >200m into forest
Edges and animal distributions
eg 1 Coastal scrub, California
Matrix - urban
Increased run-off
Reduced native spp cover
---> increased abundance Argentine ant
reduced native ant diversity
Suarez et al. 1998 Ecol 79 2041-56
Edges and animal distributions
eg 2 and 3
Manaus, Brazil
Reduced overstory
Increased understory
Higher temp
Reduced moisture
Wog Wog, Australia
Increased tree fall
Higher temp
Edges have
different
beetle
communites
Reduced leaf litter,
Edge effects on inverts +ve and -ve
Edges and animal distributions
Edge effects on mammals are often +ve or
neutral
Why? Foraging opportunities at edge
or adjacent areas + taller vegetation
for other needs
Deer
Bats
Deer mice
Martens and Weasels
Edges and animal distributions
Edge effects on Mammals can be –ve
Atlantic rainforest
Southeastern Brazil
Primates are hunted - “bush meat”
Hunting extends several km in from
edges
Hunting major cause of extirpation
from small patches
Area-sensitive songbirds
0/16 spp breed
6/16 species breed
Are more sensitive to the edge:core ratio
Edge effects on birds – biotic factors
Predation - early data
Andren and Angelstam 1988
Sweden
Wilcove et al. 1986
Eastern North America
Edge effects on birds – biotic factors
Parasitism-early data
Increasing distance from edge
Nests at edges suffer higher rates of
brood parasitism which reduces fledging
success
Gates and Gysel 1978 Ecology 59: 871-83
Take home messages
Habitat loss is a major threat to biodiversity
Habitat loss also leads to fragmentation
Fragmentation influences patch size and
configuration
Abiotic/biotic effects modify edges
Statistical and experimental methods can disentangle
the effects of loss and fragmentation