Conservation Biology - 5. Habitat Loss

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23 Mar 2012
Conservation Biology: Lecture Notes
5. Habitat Loss
- Habitat defines the natural conditions where a species lives
- Habitat loss is the primary cause of extinction worldwide as it is the most serious
threat to biodiversity
- Habitats are not created equally, difference habitats result in different demographic
performance (niches, source and sinks).
-Source habitats: birth exceed deaths
-Sink habitats: deaths exceed births (immigration is higher into a sink habitat)
- Conservation is not only concerned with where the species are found, but also how
the population is doing demographically in variable conditions found in its
geographical range
- Not all habitat loss has similar consequences (some habitats are better than others)
- Habitat loss today
Most habitat loss occurred by 1950
83% of the planet transformed
60% of all ecosystems highly transformed
- Outcomes : Loss unfolds in many ways, from outright destruction (urbanization to
indirect forms of change (pollution, eutrophication)
- Effects:
1. By definition, populations will be dramatically smaller,
2. Sampling effect (populations outright eliminated),
3. Less places to make a living
- Theoretical implications:
Population change is regulated by two major factors: rates of birth and death
and the population size at time X (N).
With deaths and N necessarily decreasing, then the dynamics of the population
are sure to change too.
- Is there an extinction debt? How
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Just because a large amount of species aren’t going extinct today, it does not
imply they won’t fall to extinction in the future as it can take 1000s of years
for complete extinction to occur
- Case Study: Norris & Stutchbury 2001
Methods; tracked birds in fragmented areas of Pennsylvania (radio-transmitters)
85% moved 40 m -2.5 km, BUT, no bird traveled >450 m over fields
40% of matings are extra-curricular…females mate with multiple partners
Benefits: guaranteed mating, with the possibility of further maximizing fitness
Costs: this large social network breaks down with habitat loss…
Findings: The population is present and mobile, but fragmentation prevents
- Scaling down and the “Appearance Enigma”
How do the mechanisms that create and maintain diversity change when habitat
size is reduced from 10 thousand hectares to ten hectares?
Appearance enigma: it looks like suitable habitat but something is profoundly
Major issues: trophic collapse, edge effects, dispersal limitations
Ex: Traps
oA sink the looks like a source
oHabitat appears favourable but lacks the resources to ensure a full
reproductive cycle
oTypified in many human-influenced regions, particularly due to agriculture
Solutions to habitat loss
- Protected areas: stop the loss
- Protection in unprotected areas
- PVA and MVP: determining how small is too small
- Restoration Ecology: rebuilding what’s lost
Protected Areas
- “Protected areas” can mean different things for different cultures. The IUCN defines
it as :An area of land and/or sea especially dedicated to the protection and
maintenance of biological diversity, and of natural and associated cultural resources,
and managed through legal or other effective means
- Currently about 12% of earth surface is protected [IUCN]
- They are clumped globally and are not evenly distributed across terrestrial eco-
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