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Lecture 5

BIOC63Fall2013 Lecture 5 Notes.docx

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Biological Sciences
Karen Williams

BIOC63Fall2013 Lecture 5 Notes: Threats to Biodiversity I Global main threats to biodiversity o Biggest affect of drivers is on land use  changing natural landscape via deforestation, fragmentation etc. o And biotic exchange – invasive species o Biome-specific threats to biodiversity o expected changes for 2100 in the main 5 drivers of biodiversity change o o these 5 threats do not have the same effect on each of the different evosystems o land use: strongest in the tropics mostly because that is where it is mostly occurring right now (for example in the North temperate areas that needed to be deforested, they already have been)  i.e. most new land clearing is occurring in the tropics o nitrogen deposition: highest where places are very industrialized, hence why it is 5 in the N temp areas o biotic exchange: med environments = open vegetation (ex: forests aren’t fully closed), which makes them more easily invadable + areas where lots of people live o climate: tropics has the least impact because there is already no seasonality there so the temperature change for example wouldnt make as big as a difference as in the Arctic Passenger pigeon o best document extinction o used to be world’s most numerous bird o made up 30-40% of all NA birds o human exploitation of mass flocking and also were used as poor people’s foods  a lot of birds were taken out at once o also people did not hunt just the adult but also the eggs o so the bords could notrejuvenate their generations o and they also had nests all in the same site o so a lot of killings would occur at once  population was not able to re-establish its numbers o with new communication systems and faster transportation = easier tracking of birds and more hunting o first declines occurred by 1860 o scattered birds could not breed o captive breeding failed o last bird died in Cincinnati zoo Sep 14, 1914 (her name was Martha) o E.O. Wilson  no species is abundant enough to be immune to extinction Sustainable Exploitation of wild species o Conditions: o Keep captive communities o Regulate on reserve o Set capture limits (control) o Hunt fraction of population – only adults o Maintain genetic diversity 1 o Avoid exploiting species that are already threatened o Habitat preservation o Temporal control (only hunt at specific times) o 1. Exploitation rate must be smaller than replenishment rate o 2. in roder for the population ro remain above minimal population size o 3. Retention of natural ecosystem role* o 4. No permanent alteration of size distribution, age structure or sex ratios* o 5. retention of social behavior* o * Darwin’s legacy Overexpolitation occurs… 1. If animal product is rare and cannot be replaced by anything else 2. Money has to be invested in coming up with machinery to exploit animals (new harvesting techniques) people continue doing it because they paid for the machinary 3. Failing regulation or disincentives  We have a weak legeal backbone 4. Weak law enforcement 5. In poor countries, they do not have means of doing things differently  few alternatives for impoverished people 6. We don’t have knowledge about the species demise coming up  no knowledge about when limits are reached Consequences of overexploitation o Dwindling population sized  (local) extirpation  (global) extinction Reasons for overexploitation o Food o Trophy hunting o Pet trade o Medicine Human driven-extinction o Humans arrive  megafaunas go extinct o Throughout human dispersal history, arrival of human on certain continents coincides with m
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