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Conservation Biology - 4. Five Riders of the Apocalypse

Course Code
BIOL 3130
Andrew Mac Dougall

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Conservation Biology: Lecture Notes
4.Five riders of the apocalypse
1. Habitat degradation ( primary cause of biodiversity loss )
- Conversion to unsuitable habitat
- –Resource extraction, agriculture, settlements, pollution
- Affects 60% of the earth’s ecosystems
- Protection
- Modification (ecoforestry…)
- Restoration and recovery
2. Habitat fragmentation (secondary cause of biodiversity loss )
- The reduction of area covered by the habitat type; smaller population size
- Isolation
- Less habitat diversity, loss of heterogeneity
- Edge effects
- Vulnerable species: rare, large home ranges, limited dispersal, demographic
- Corridors
- Modified land use
- Gene flow (transplants, transport) – bring in other populations
3. Overexploitation
- Hunting, harvesting or collecting, fishing
- Extinction, extirpation, population reductions
- Cascading effects within food webs
- Sustainable exploitation, fairer compensation, re-introductions
4. Species invasions
- Accidental or intentional introductions
- Often associated with human disturbance
- Species loss, reduced ecosystem function
- Biological control, eradication, prevention

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5. Climate Change
- Release of stored carbon; 30% more atmospheric CO2 than prior to the industrial
- Altered temperatures & precipitation: where, when, and how much.
- Continental migration corridors severed
- Reduced emissions, reduced consumption, increased carbon sequestration
(removing carbon from the environment, alternative energy supplies (solar, wind,
Five major factors: the big picture
- All affect the mechanisms that create and maintain biodiversity, all systems usually
undergo all these 5 effects simultaneously
Direct effects:
- Displacement of populations
- Elimination of populations (sampling effect)
- Reduced demographic performance (births vs. deaths)
Indirect effects:
- Each can change the intensity, direction, and outcome of biotic interactions, within
and across trophic levels (ex: eliminating predators results in uncontrolled
herbivores leading to a brown wold)
- All interact: positive and negative feedbacks
- Elevated CO2, eutrophication (i.e. fertilizers), and invasion: C sink or C source?
Fertilization by higher CO2 and eutrophication, combined with more
productive invaders
Results in significantly higher production
C sink (accumulation of carbon in the soil (sequestration), offsets global CO2
emission increases)
But, higher soil respiration
C source (releases carbon into the environment, and accelerates CO2 levels
in the atmosphere)
Complication : carbon sinks can become sources! Plants and trees are
temporary C-sinks (they sequester Carbon and therefore remove it from the
atmosphere), but once they die and begin to decay they actually release
Carbon, so they can also be C-sources.
Implication : we are looking for long-term carbon sinks to counter climate
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