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 km 2 per year Canada - 10,000 km 2 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 Length of edge Length of edge 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 Reduced leaf litter, Edges have different beetle communites 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