Biology 106 Lecture Topic # 25 Conservation Biology /Extinction
I. Conservation Biology - relatively new area
- developed in response to biodiversity crisis
- The study of species richness at many levels of biological organization:
For example: 1. ecosystem 2. community 3. species 4. populations 5. individuals
Utilizes concepts and knowledge from:
1. population genetics 2. evolution 3. ecology 4.wildlife management
Terminology:
Endangered = survival and repro. in immediate jeopardy for one or more causes.
Rare = not presently threatened by extinction, but exist in small #'s and could become endangered if present envir. worsens.
Threatened = not presently endangered with extinction, but may become endangered without special protection and management.
II. Concept of Rarity:
1. always rare
2. rare as a new state, ex. from a relatively recent popln bottleneck
When is the best time to try to save a spp???
III. Causes of Extinction - linked to human activities for 1,000's of years.
#1 Overexploitation - i.e., overhunting
Islands:
ex. Polynesian people settled Hawaii and rapidly exterminated 39 spp endemic land birds (incl. 7 spp geese, 2 spp flightless ibises, 7 spp flightless rails, > 15 spp finches)
ex. Maori people colonized New Zealand - #'s of species of large flightless birds lost.
Mainland Continents:
ex. Lg. animals in N. Am. -greatest losses 20,000 ybp following coloniz. via Bering Land Bridge
ex. Australian fauna 13/15 genera extinct
ex. Passenger pigeons in N. Am. - most numerous in early 1800's, extinct by 1914
#2 Habitat Destruction - humans need to be fed, clothed and housed. Agriculture and forestry have coopted = (designated for human use) > 30% of all terrestrial production and % is rising
- remaining spp have only 2/3 of total global terrestrial production available and % decreasing
ex. loss of tropical forests, old-growth temperate forests, natural grasslands, and estuaries
a. Habitat size/fragmentation, Patch = Island dynamics, where suitable habitats are separated by uninhabitable areas. Edge effects more of a problem in smaller reserves.
#3 Introduction of Predators and Disease - migration of humans also brought many species of organisms from one continent to another. Seeds of weedy species contaminants in crop seed bags. Despite quarantines, diseases spread rapidly.
-Introduced spp have caused the extinction of 1,000's of native plant and animal spp world-wide
Mainland:
-pheasants intro. N.Am.
- intro. rabbits & foxes to Australia. Almost 1/2 of all small marsupials and rodents in Australia extirpated in last 100 yrs due to competition with rabbits and pred. by foxes.
Islands: existed under relatively predator-free conditions
- loss of many flightless birds as result of them evolving under predator free conditions
- Black rats invade Galapagos islands and out compete native rice rats
- pigs and black rats routinely excavate all nests of Galapagos tortoises and eat eggs
Pest outbreaks in new environments:
ex. Chestnut blight - fungus eliminated Am. Chestnut, once dominant in Appalachian Mts.
ex. Dutch elm disease - fungal disease from Asia. First noted in 1920, reported in N.Am. in 1930. Disease caused extinctions throughout time but not well preserved in fossil record.
#4 Climate Modification? - no species is known to have been extirpated by current global warming. However, past climatic changes, particularly cooling, resulted in many extinctions
IV. Spp Survival: Assessment, Prioritization and Management
1. Assessment:
Popln Viability Analysis - popln size nec. to persist in nature/risk of extinction during given time period
Factors involved:
a. Demographic stochasticity = am't of variation in birth and death rates. Linked to life history and popln size. small vs. large
b. Genetic stochasticity = am't of genetic variation w/in popln. Linked to life history strategy and popln size. small vs. large
c. Habitat availability
d. Knowledge of basic biology of endangered organism
e. Distribution - i.e., local vs. endemic
ex. African Cheetahs
ex. SI Lakeside Daisy
2. Prioritization for Conserving Species:
a. Taxonomic distinctiveness
b. #'s of closely related other taxa
c. Less priority assigned to hybrids
d. Animals vs. Plants
e. Cost effective decisions
3. Management Strategies:
Animals - captive breeding programs involve info. of basic biology of spp such as nutrition & reproduction, and alot of physical space
- temporary measure, buying time, until habitat available &/or overexploitation halted
- initially occurred in Zoos
- record keeping of matings poor
- inbreeding depression documented in many captive breeding programs
Now know from Popln Genetics that: (applies to both animal and plant captive breeding programs)
1) all indiv's should mate at equal freq.
2) popln sizes should be large
3) minimize selection in captivity
ex. Speke's gazelle
Plants - Propagation practices lend themselves to more long term management practices.
1. Temperate long term seed viability. Tropics less, where most untapped spp diversity remains.
2. Pollen storage
3. Tissue culture
4. Clonal Preservation
5. Botanical Gardens
Costs????
V. Restoration Ecology - new area of research, to regenerate habitat presently disturbed/destroyed.
- Largest restoration project currently underway at Guanacaste National Park in NW Costa Rica
Goal = restore large area of tropical dry forest, the most threatened ecosystem in Central Am.
- save from small fragments left among large cattle grazing areas
-Strategy for overall ecosystem and poplns of species inhabiting an area. A matter of scale. Issues concerned with are: 1. popln size,2. habitat size, quality to maintain popln,
3. demography/ life history, 4. genetic variation / inbreeding...