Lecture 23 Ricklefs notes

The Biodiversity Crisis (Allan, Monday Dec. 7)

Assigned readings: Ricklefs Chapter 26 (all), Chapter 25 (p. 535-537)

Chapter 26: Biodiversity, Extinction, and Conservation (p. 545-569)

Biological diversity has many components
Estimates of global species counts are between 10 million and 30 million
Different types of diversity:
Ecological diversity: a measure of biodiversity that takes into account variation in the ecological roles of species
Genetic diversity (between and within species): a measure of the genetic variation in a population, species, or community – crucial to evolutionary responses of populations to changes in the environment
Phylogenetic diversity: a measure of biodiversity that takes into account the degree of relationship among organisms, giving greater weight to more distantly related forms
Geographical diversity: diversity based on endemic species (species whose distributions are limited to small areas)
Conservation of global biodiversity is best accomplished by directing efforts toward areas of high endemism (large numbers of endemic species) as well as high diversity

The value of diversity arises from social, economic, and ecological considerations
Some estimates suggest more than one species disappears each day
Accelerated loss of species is directly linked to the growth and technological capacities of the human populations

Why should we care?
Moral responsibility: if morality derives from a natural law-that is, if morality is intrinsic to life itself-then we may presume that the rights of nonhuman individuals and species are as legitimate as the rights of individuals within human society
Economic benefits: food resources, game species, sources of natural products, drugs, and organic chemicals, domestic use, ecotourism
Ecotourism: the practice of visiting an area to see unspoiled habitats and the animals and plants that live in them
Responsible for the development and maintenance of an increasing number of parks and reserves in many parts of the world
Flagship species: highly values species (ex. giant pandas, cheetahs, etc.)
Indication of environmental quality
Example: The peregrine population was a sensitive indicator of the general health of the environment in the mid 1900's due to DDT and related pesticides
Maintenance of ecosystem function
Species diversity may have intrinsic value for stabilizing ecosystem function

Extinction is natural but its present rate is not
The present rate of decline and loss of species locally and globally is a stark indicator that many ecological systems are deteriorating
Three types of extinction:
Background extinction: the turnover of species (a relatively low rate)
Information comes from the fossil record - about 1 species extinction per year
Mass extinction: the dying off of large numbers of species because of natural catastrophes
Anthropogenic extinction: extinction caused by humans

Human activities have accelerated the rate of extinction
Red List of the International Union for the Conservation of Nature (IUCN) ranking scheme: critically endangered, endangered, endangered, and vulnerable
Habitat loss and fragmentation
The effect of reduced habitat on species richness is a direct extension of the theory of island biogeography (smaller islands support fewer species)
Fragmentation can reduce the dispersal of individuals, turning large populations into metapopulations
Effects of habitat fragmentation may be compounded by the increasing rate of global warming

Small population size
Every population experiences stochastic/random variation in population size
Stochastic extinction increases with habitat fragmentation
Small population size further increases the probability of extinction by reducing genetic variation in a population

Extinction caused by overhunting and overfishing is not a recent phenomenon
Species introductions can have negative effects on native biota (especially in aquatic ecosystems)

Emerging diseases
Emerging disease: one that has appeared in a population for the first time, or that may have existed previously but is rapidly increasing in incidence or geographic range
Examples: HIV, West Nile virus, H5N1

Vulnerability to anthropogenic extinction
The difference between success and failure in natural systems may hing on very small differences in breeding success or longevity
Small species are vulnerable to anthropogenic extinctions primarily because of external factors (small geographic range size, etc.)
Larger species are vulnerable because of intrinsic qualities (long development periods, etc.)
Smaller species might benefit more from the general protection of threatened habitats, whereas larger species require closer individual attention to particular factors that influence their survival and reproductive success

Reserve desgins for individual species must guarantee a self-sustaining population
Minimum viable population (MVP): the smallest population of the species that can sustain itself in the face of environmental variation
The design of nature reserves must take into account the ecological requirements and MVP of the species of concern

Critical habitats and geographic areas for conservation
The most valuable areas are those that provide havens for the largest numbers of species not represented elsewhere
Establishing nature reserves often conflicts with economic interests
Example: The timber industry versus the habitat requirements of the spotted owl (Washington and Oregon)

Design of protected areas
Population viability analysis (PVA): incorporates demographic information about a particular population into a simulation model to predict the probability that it will avoid extinction within a given period
Ecological principles derived from metapopulation theory and the theory of island biogeography can also help planners to arrive at the best design

Some critically endangered species have been rescued from the brink of extinction
Many species have come so close to extinction that their preservation has required exceptional human intervention
Often captive breeding and reintroduction programs

Chapter 25: Landscape Ecology (p. 535-537)

Habitat fragmentation can affect species abundance and species richness
Habitat is fragmented when human activities or natural events divide a large, contiguous area of habitat into several smaller habitat patches (either terrestrial or aquatic)
Habitat fragmentation produces five effects:
1. Total amount of habitat decreases
2. Number of habitat patches increases
3. Amount of edge habitat increases
4. Average patch size decreases
5. Patch isolation increases

Habitat fragmentation and biodiversity
Habitat fragmentation commonly causes a reduction in species richness

Habitat fragmentation and species abundances
Edge specialists: some species that benefit from habitat fragmentation if they are specialized to live in ecotones between two habitat types

Fragment shape and species abundances
A circular fragment would contain the minimal amount of edge habitat, whereas a long, slender fragment of the same area would have a much higher proportion of edge habitat

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