Transcript Habitat Loss and Fragmentation

Map of remaining significant
woodlands in Southern Ontario.
Used to be all woodlands before settlers
arrived.
Map shows the distribution of
converted natural areas in Southern
Ontario to human uses (orange).
In a 60 year period from 1861 to 1921 the forest cover of Carolinian Canada
dropped from 77% to 19 %. In the same time frame, 70% of southern Ontario
wetlands were lost. Since that point in time, there has been a slight recovery of
forests in some parts of the area but overall the decline and degradation in natural
habitats continue.
Map shows the extent and
distribution of parks and protected
areas in Southern Ontario.
The Process of Habitat Fragmentation (arrows show increasing fragmentation of habitat)
Each new construction results in
smaller, more scattered habitats.
The outcome is population reduction
and isolation for native species.
Urban sprawl produces fragmentation and a loss of
biodiversity on the planet
Habitat Destruction, Loss, Degradation…
At least 83% of the Earth’s land surface has been
transformed by human activities
(Sanderson et al. 2002)
About 60% of Earth’s ecosystems are considered
degraded or unsustainably used
(Millennium Ecosystem Assessment 2005)
98% of U.S. streams and rivers have been fragmented
(see next lecture) by dams
(Benke 1990)
Habitat Destruction, Loss, Degradation…
Habitat degradation – impacts that affect many, but not all species;
some of which may be temporary
Habitat destruction & loss – impacts that affect nearly all species;
time scale for recovery is very long
How do humans destroy and degrade habitats and ecosystems?
E.g., agricultural activities, extraction activities,
certain kinds of development
These are often considered to be the most important direct threats to
biodiversity, since they eliminate species, reduce population sizes,
and reduce performance of individuals
Habitat Destruction, Loss, Degradation…
Loss of forest habitat in Borneo
Image of shrinking forest cover on Borneo from www.planttreesaveplanet.com
Rare species are especially vulnerable
Small populations are especially prone to extinction
E.g., Hawaii’s
native bird species
Half went extinct
soon after the
Polynesians arrived
Image of extinct Hawai’i ’Ō’ō (Moho nobilis) from Wikipedia
Half of the
remaining species
went extinct soon
after Captain James
Cook arrived
Habitat Destruction, Loss, Degradation…
Loss of ice from polar ice cap
1979
2003
Minimum sea ice concentration; 9% decline per decade
Images from www.nasa.gov
Biodiversity Hotspots
Usually defined by species richness, endemism & threats
Map from www.fao.org
Biodiversity Hotspots
Usually defined by species richness, endemism & threats
These hotspots of biodiversity cover only ~1.5% of the Earth’s land;
if they were destroyed ~1/3 of Earth’s species would go extinct
Figure from Myers et al. (2000, Nature)
Designing Nature Reserves
Biodiversity can best be sustained by large
reserves connected across the landscape and
buffered from areas of intense human use.
The Best Spatial Configurations for a Core Natural Area or Nature Reserves
Larger blocks support larger and more
stable populations and communities.
1 large area is better than an equal
area composed of many smaller areas
because there is less outside
influence.
The closer ecosystem fragments are
to each other, the greater the chance
populations will be able to use the
entire area.
Interconnected areas provide
wildlife corridors and permit
migration between larger blocks.
Buffer zones protect fragmented
ecosystems from outside influences.
Extensive annual surveys began in the Ontario core areas in 1992 to
monitor the Loggerhead Shrike population. During these surveys
information on the number of pairs and single birds and their habitats
is collected with the help of volunteers. As shown above, the number
of shrikes in the province decreased substantially between 1992 (55
pairs) and 1997 (17 pairs). In 1998 the population rebounded slightly to
30 pairs, which is similar to numbers counted in 1995 and 1996. The
Ontario population is currently at extreme risk of extirpation.
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