Download 2 components to Habitat Fragmentation

Habitat Fragmentation
2 components to Habitat Fragmentation
• 1) Reduction of some habitat types in a landscape
• 2) remaining habitat is distributed in smaller, more isolated patches
• Impact on biodiversity will be dependent on the natural patchiness of the
habitat
• 2 types of Habitat Fragmentation:
• 1) islands
2) shreading
Habitat Shredding (Essay 9a
- Feinsinger 1997)
• Suggests that shredded landscape is better than island fragmented
landscape
• Shredding can be worse than island fragmentation if the strips are
too narrow (edge effects everywhere)
• Metapopulation models do not fit shredded habitat
• Need new models and more study off this type of habitat patch
Edge Effects
• Habitat fragmentation increases the amount of edge habitat relative
to the amount of interior habitat.
• Characteristics of Edge Habitat:
• 1) increased light, increased temperature, noticed effects up to 40 m
in Amazon forest (Kapos 1989)
• 2) Increased wind - results in more wind stress, increased dryness
(soil and air), strong effects up to 200 m, see effects up to 500 m
(studies in Australia and Pacific NW)
Edge Effects
• 3) increased fire risk caused by combination of increased temp.,
wind, and light
• 4) Increased predation/easier access - very big problem for birds
and small mammals
• 5) Increased competition from exotics and common native species
• Note: most terrestrial game are edge adapted so increased edge
habitat has been promoted by wildlife managers in the past
Edge Effects
• Some habitat fragments can be so small that they are all edge and
no interior habitat
• Doug Fir in Pacific Northwest: with a 50% cut in the standard
checkerboard pattern, remaining habitat is all edge
Crowding Effects
• Temporary increase in density of individuals due to loss of
surrounding habitat
• documented in the tropics (Leck 1979, Lovejoy et al 1986) and in
temperate habitats (Noss 1981)
• Reach carrying capacity and collapse
• Habitat actually becomes a sink
Case Study - Flattened Musk Turtle
• The SE US has a large percentage of endemic fauna of mollusks,
fish, turtles due to numerous river drainage systems
• The Flattened Musk turtle is one endangered endemic
• Due to habitat destruction only 7% range is remaining
• Remaining habitat is fragmented in such a way that make migration
impossible
• Local populations are in danger of extinction because of disease,
reducing breeding
Dung Beetles
• Dung beetles are keystone species in forest ecosystems
• Researchers studied effects of habitat fragmentation in the
Brazilian Amazon on dung beetles (Klein 1989)
• Surveyed fragments of 1ha, 10 ha, continuous forest and
clear cuts
• Smaller fragments had fewer species, lower densities, and
smaller-sized beetles
• Dung decomposed at a lower rate
Raptors of Java
• 150 million people in 132,000 sq. km
• originally tropical forest, only 10% remains in reserves
• Research project studied effects of habitat fragmentation on 10
raptor species (Thiollay and Meybury 1988)
• Reserves had high densities of birds, numbers of species increased
with size of reserve
• used as nesting grounds for forest birds but dispersed for foraging
Raptors of Java
• Problems:
• 1) Non-forest species, osprey, sea eagle do not nest in reserves and
habitat is not protected
• 2) Many fragments are less than 100 sq. km and will not support
viable populations
• 3) Not much habitat left for conservation - would have to
restore/convert agricultural land to preserve the raptors that are
declining rapidly
Biological Consequences of Habitat Fragmentation
• Genetic?
patches, local heterozygosity,
inbreeding
Drift between
regional heterozygosity,
• Population?
• Lost, increase, decrease, species mobile and moves between
patches, species less mobile and becomes divided
• Species?
• Increase diversity, decrease diversity, increase richness, increase
richness, change balance and interaction, increase exotics
Biological Consequences of Habitat Fragmentation
• Ecosystem
Lost, Greatly
reduced, fragmented, change in community structure, change in the
balance of ecological processes may change (species interactions,
nutrient cycling, fires)
• Landscape?
Gamma diversity
may decrease, proportion of ecosystems may change, Historical
patterns of fire may change, Corridors will be lost and gained
Biological Consequences of Habitat Fragmentation
What about the effects of climate change on species in a
fragmented landscape?
Roads as Barriers
One of the hottest new areas of research
- impacts have been documented in amphibians, insects, small mammals,
large mammals, plants
- Few studies of long-term effects on population dynamics, genetics
Genetic studies
White footed mice Canada (Merriam et al 1989) - no effect He, genetic drift
Tropical trees (Hall et al. 1996) - decrease He
Common frogs (Reh and Seitz 1990) - decrease He
Natural Fragmentation
• In many ways, natural habitat is fragmented
• Landscapes are mosaics of different habitats and the patchiness
changes over time due to succession, fires, climatic fluctuations
• If conservation biologists claim/believe that human-caused habitat
fragmentation is bad for biodiversity: we must be able to outline
the fundamental differences between natural habitat mosaics and
habitat fragmentation
3 Hypotheses
• 1) Natural patches have a complex structure of diversified habitats,
human-altered fragmented landscape has simplified patches
(parking lots, buildings, clearcuts, agriculture)
• 2) Natural landscapes have natural edges with less contrast than
human fragmented landscapes
• 3) Some features of human habitat fragmentation - like roads pose
specific threats to population viability
Complications
• Island biogeography theory, species area/curves, landbridge island
data all suggest that habitat fragmentation will result in a decrease
biodiversity
• Habitat fragmentation has been shown to not change or even to
increase bird diversity in some studies
• Habitat fragmentation occurs on many different scales, the point at
which habitat fragmention results in a decline of biological
integrity is unclear
What can be done?
• We need more long-term research on impacts of habitat
fragmentation
There is a lot to be
done!
Use
these data to:
• Design Optimal Reserves Systems
• Design forestry strategies that minimize impacts
• Restore ecosystems
• Plan road systems, corridors