CH 58 CONSERVATION BIOLOGY & BIODIVERSITY
- Biodiversity is examined at 3 levels: genetic, species, and ecosystem diversity.
- Endangered species: those in danger of extinction
- Threatened species: those likely to become endangered in the future.
- Conservation biology uses principles and knowledge from molecular biology, genetics and ecology to protect the
biological diversity of life at each of those 3 levels.
58.1 Why conserve biodiversity?
- We have an ethical responsibility to protect what are our only known living companions in the universe
- humanity has obtained lots of benefits from foods, medicines, and industrial products derived from plants, animals, and
- Preserve essential services provided by ecosystems: clean air and water.
Preservation of biological Diversity can be justified based on the ecological and economic values of diversity as well as on
- World’s ecosystems were worth more than $33 trillion per year, twice the gross national product of world’s economies
- Estruaries are important for nutrient cycling, water supply and disturbance regulation.
How much diversity is needed for ecosystems to function properly?
- Rivet hypothesis: (Erlich) species are like the rivets on an airplane, each playing a small, critical role in keeping the
- Redundancy hypothesis: (Walker) most species are like passengers on a plane, take up space but don’t add to the
airworthiness. These species are redundant because they could simply be eliminated or replaced by others with no loss
in function and airworthiness is affected by activity of a few keystone species.
- Idiosyncratic hypothesis: (Lawton) ecosystem function changes as number of species increases or decreases but
direction of change is not predictable
Field experiments suggest biodiversity is important for ecosystem function
- Tilman and colleagues: sowed plots with seeds of up to 24 different species of prairie plants and replicated 21 times.
- More diverse plots increased productivity and used nutrients such as nitrate more efficiently.
- There may also be a point at which ecosystem function is maximized – additional species appear to have little or no
impact, supporting the redundancy hypothesis.
58.2 The causes of Extinction and Loss of Biodiversity
- extinction: process by which species die out, with background extinction rate of about 1 species to be extinct every 1000 years.
- This method may be biased to fossil records
- Polynesians who colonized Hawaii are responsible for extinction of half of 100 endemic land birds
- Biodiversity crisis: elevated loss of species. The main causes of extinction are habitat destruction, direct exploitation, and introduced species
- Movement of species correspond to climate change
- Habitat loss results from agriculture and urbanization whereas overexploitation was a main treat of marine animals.
1. Habitat destruction
- Deforestation: conversion of forested areas to nonforested land.
- More than 10% of mammals have an obligatory relationship with forest cover, depending on trees for food and nesting
- Scouring of land to plant agricultural crops, creates soil erosion, increased flooding, declining soil fertility, silting of
rivers and desertification.
2. Direct exploitation
- Hunting of animals
o Ex. Passenger pigeon used to be most common bird in N. America, hunted to extinction for its meat
o Great auk also hunted for meat and feathers.
o Stellar’s sea cow hunted to extinction 27 years after discovery.
o Dodo bird, flightless hunted for meat and its eggs were destroyed by rats, pigs and monkeys brought to island
3. Introduced species
- Exotic species introduced for agricultural purposes or as sources of timber, meat or wool.
- Invasive: spreading / outcompeting native species for space and resources.
o Ex. Brown tree snake was accidentally introduced to Guam decimated country’s native bird populations.
Small Populations are Threatened by Loss of Genetic Diversity
- Treats to species from small population size relate to reduction of genetic diversity:
- Mating among genetically related relatives
o Ex. Inbreeding of greater prairie chicken after their homes were converted to farmland, decrease in
population 250 000 50.