Lecture 23: Potential Exam Questions
  1. List and briefly describe the three phases of the 6th great extinction (caused by human influence).

Phase 1: 100,000 years ago with the spread of humans
Phase 2: 10,000 years ago with the dawn of agriculture
Phase 3: 250 years ago with the industrial and scientific revolutions

  1. List the 6 threats to biodiversity. Describe 3 in more detail, with an example.

Over-exploitation, invasive species, habitat destruction, climate change, pollution, domino effects
Over-Exploitation
* examples: passenger pigeon, dodo, bushmeat harvest (often ancillary to other kinds of development - forests are practically emptied), cod overfishing
Non-indigenous species
* Asian carp escaped from aquaculture in the southern states - electric fence at the Great Lakes to block them - carp DNA has been found about the fence; will compete with perch in Lake Erie (both planktivores)
* Zebra mussels (from Europe) in the Great Lake and Hudson River - filter algae out of bethic/pelagic zones - no longer anything to eat for other organisms; water clarity from filtering has led to an increase in submerged aquatic plants
* Nile Perch in Lake Victoria introduced for commercial fishery (highly successful) - threat to endemic cichlids - will likely cause hundreds of species extinctions
* Great Lakes sea lamprey led to the collapse of take trout
* gypsy moth in Michigan defoliates trees
* Causes of invasive species:
* colonial nostalgia
* introduced for angling
* fish culture escape
* pet trade
* inter-basin transfers
* biocontrol
* Invasion success depends on:
* aspects of invader and receiving environments
* resistance of habitat
* High success rates but not all are harmful, especially not permanently
* Best determinants for success are past history of success, broad environmental tolerance, ability to thrive in human-altered environments, similarity of source and recipient environments, large propagule size and multiple events
* Tilapia, carp, rainbow trout all highly successful
Habitat Loss and Fragmentation (most important driver of extinction)

  • Habitat fragments too small to maintain viable populations and too isolated for rescue efforts from other pathces - very small population is on its own
  • Conservation strategy - corridors and connectivity

Climate Change

  • Gradual species distribution will shift poleward - depends on adaptability, habitat occupiable - will the whole community move together at the same rate? - will disrupt community interaction

Challenge to place-based conservation - range limit for species shifts but natural preserve boundaries do not
Domino Effects

  • System collapses - one species goes extinct so do all the other species that depend on it (not much evidence for this)
  • e.g. black-footed ferret rare because prairie dog was hunted
  1. How fast are extinction rates occurring today? How do we know the rate of extinction?
  • 1,000 to 10,000 faster than any time in the past 600 million years
  • estimate probable number of species, estimate habitat loss, and then use species-area relationship for determine species loss (similar effect as reasoning for fewer species on small islands)
  • Expect 25-50% extinction of the world's species by 2100 based solely on habitat loss
  1. Describe the protected lands strategy for biodiversity conservation
  • Protected lands - now 12% of planet - well-protected and small areas can do well
  • Goal is to increase protected area and distribution by ecosystem type - uniqueness, hot spot, endemism, gaps in current protection
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