Biodiversity and Conservation Biology
Chapter 53
Biodiversity
Biodiversity is the richness of living systems
Genetic variation: the raw material for adaptation, speciation, and evolutionary diversification
Species richness: the number and variety of species within a community – influences its overall characteristics, population interactions, and trophic structure
Ecosystem level: complex interactions bind species in an ecosystem together, and different ecosystems interact within the biosphere
53.1 The Biodiversity Crisis
Biodiversity is declining dramatically, perhaps faster than ever before in Earth’s history
Three broad threats are caused by humans and exacerbated by global climate change:
Clearing of forests (deforestation and desertification)
Commercial overexploitation of marine fish populations
Hydrologic alterations of freshwater ecosystems
Deforestation
Global deforestation occurs at a rate of 13 million hectares per year
More than 90% of occurs in tropical regions
Forests most often cut for grazing livestock
25% of all deforestation in Brazil, which has 27% of the planet’s above-ground woody biomass
Most forests are burned as they are cleared
Adds CO2 to the atmosphere, enhancing global climate change
Deforestation also reduces the amount of carbon (CO2) removed from the atmosphere by photosynthesis
Deforestation- Amazon Basin
Tropical Rain Forests
~ 50% have already been cleared globally
Cleared to harvest valuable timber, and to make way for subsistence farming.
Deforestation
Temperate forest of North America
Clearing began with arrival of European settlers.
Cleared to harvest timber & turpentine, and for agriculture.
< 1% of the original temperate forest in southeast US survives.
Desertification
When large tracts of subtropical forest are cleared and overused, the land often undergoes desertification:
Groundwater table recedes to deeper levels
Less surface water is available for plants
Soil accumulates high concentrations of salts (salinization)
Topsoil is eroded by wind and water
Desertification speeds the loss of biodiversity locally, sometimes eliminating entire ecosystems
The Sahel Region of Africa
Overexploitation
Excessive harvesting of an animal or plant species (overexploitation) can cause evolutionary changes and local extinctions
Overexploitation severely threatens marine ecosystems
Yield of fish stocks in Grand Banks has declined to less than 10% of highest historic levels
Cod now mature at a younger age and smaller size
The Grand Banks: Cod
Hydrologic Alterations
Hydrologic alterations (such as dams) are changes to the pathways through which water moves in the hydrologic cycle
Water is used for agricultural, industrial, homes; generate hydroelectric power; mitigate flooding
Hydrologic alterations have practically eliminated some freshwater ecosystems – including the Nile and the Colorado River
More than 30% of the native species in North America are now threatened with extinction
Three Gorges Dam
Water Use and the Florida Everglades
53.2 Specific Threats to Biodiversity
When humans colonize a habitat, they build roads and clear isolated areas for specific uses – reducing areas of intact habitat to small, isolated patches (habitat fragmentation)
The combination of small population size and genetic isolation reduces genetic variability and fosters extinction
Habitat Fragmentation
Habitat Fragmentation
Habitat fragmentation
Reduction to small, isolated patches
Smaller patches, lower carrying capacity
Patches separated by unsuitable habitat
Increasing edge effects reduces remaining habitat quality
Local environmental changes
Songbird reduction from habitat types, brood parasitism and nest predation
Experimental Research:
Predation on Songbird Nests
Habitat Fragmentation
Specific Threats to Biodiversity
Pollutants are materials or energy in forms or quantities that organisms do not usually encounter
Chemical pollutants, the by-products or waste products of agriculture and industry, are released locally – but many spread in water or air on a continental or global scale
Sulfur dioxide (SO2) from coal-burning power plants and acid precipitation
Acid Precipitation
Patz, 2005. “Impact of regional climate change of human health”
Introduction of Exotic Species
The introduction of nonnative organisms (exotic species) into new habitats poses a serious threat to biodiversity
Exotic species prey upon, parasitize, outcompete native species, leading to their extinction
Many have r-selected life histories – mature and reproduce quickly, and thrive in degraded habitats
In the absence of competitors, predators, and parasites – exotics often experience exponential population growth
Starling Range Expansion
Kudzu
Hemlocks Killed by Woolly Adelgids
Spread of Disease-Causing Organisms
53.3 The Value of Biodiversity
Human activities are causing the current dramatic decline in biodiversity
Arguments for conserving biodiversity fall into three general groups:
Its direct benefit to humans
Its indirect benefit to all living systems
Its intrinsic worth
The Pacific Yew Tree and Teosinte
Indirect Benefits of Biodiversity
Humans and other species derive indirect benefits when ecosystems perform the ecological processes on which all life depends (ecosystem services)
Decomposition of wastes, nutrient recycling, oxygen production, maintenance of fertile topsoil, and purification of air and water
Photosynthetic organisms also mitigate global warming by withdrawing CO2 from the atmosphere and incorporating it into wood or shells (carbon sequestration)
Intrinsic Value of Biodiversity
Ethicists argue that biodiversity has intrinsic worth as living species, independent of direct or indirect value to humans
Countering this position is the view that human needs should always rank above those of other species and that we should use them to maximize our own welfare
This debate deals more with philosophy and public policy than biology – nevertheless, many people feel that the natural landscape enhances human existence in intangible ways
53.4 Where Biodiversity Is
Most Threatened
Researchers have pinpointed 34 biodiversity hotspots – where biodiversity is concentrated and endangered by human encroachment
A biodiversity hotspot must harbor at least 1,500 endemic plant species (those that are found nowhere else), and it must have already lost at least 70% of its natural vegetation
Locally distributed species account for much of Earth’s biodiversity; and if the local habitats where these species occur are at risk of development, the species are also at risk
Sites Where Extinctions Are Imminent
In 2005, they identified 595 locations in tropical forests, on islands, or mountainous regions where 794 highly endangered species (“trigger species”) are confined to a single site
An endangered species is one that is “in danger of extinction throughout all or a significant portion of its range”
Imminent Danger of Extinctions
53.5 Conservation Biology:
Principles and Theory
Conservation biology is an interdisciplinary science that focuses on the maintenance and preservation of biodiversity
Conservation biologists use theoretical concepts from systematics, population genetics, population ecology, and behavior to develop ways to protect habitats and the endangered species that live within them
Population Genetics
When populations are reduced to a small size, genetic drift reduces their genetic variability and evolutionary potential to adapt
The loss of even a small fraction of a species’ genetic diversity reduces its survival potential
Conservationists try to increase both the population sizes of threatened and endangered species and their genetic variation within and between populations
Whooping Cranes
Population Ecology and Behavior
Conservation programs require data about a target species’ ecology and behavior, including its feeding habits, movement patterns, and rates of reproduction
Sea otters (a keystone predator)
Hunting reduced otters to about 3,000 individuals
Populations of sea urchins (favored prey) exploded
Sea urchins decimated kelp beds, disrupting animal communities in that habitat
To facilitate recovery, conservation biologists reintroduced otters to several regions
Geographical Range of Sea Otters
Population Viability Analysis
Conservation biologists often conduct a population viability analysis (PVA) to determine how large a population must be to ensure its long-term survival
PVAs evaluate habitat suitability, likelihood of catastrophic events, and other factors that may cause fluctuations in demographics, population size, or genetic variability
When conducting a PVA, researchers must decide what level of risk is acceptable for a given survival time – e.g. a 95% probability that the species will survive for 100 years
Population Viability Analysis (cont.)
An increase in either survival probability or survival time requires an increase in the size of the population that must be conserved
The minimum viable population size identifies the smallest population that fits the specifications of the conservation plan
Example: Biologists used PVA in the conservation of an Australian marsupial, the yellow-bellied glider
The Yellow-Bellied Glider
PVA helped biologists determine which remaining forest tracts are large enough to sustain a yellow-bellied glider population
Landscape Ecology
Conservation biologists often use landscape ecology to design the size and geometry of nature reserves and other protected areas
Landscape ecology analyzes how large-scale ecological factors (distribution of vegetation, topography, human activity) influence local populations and communities
Some protected areas consist of one large habitat patch – others consist of several smaller patches
Landscape Ecology (cont.)
Some conservation biologists argue that clusters of physically separate preserves connected by corridors are most effective in maintaining metapopulations of endangered species
Studies suggest that habitat patches connected by corridors retain more native plant species than isolated patches, and that corridors did not promote the entry of exotic species
The Florida Panther
The Florida Panther
53.6 Conservation Biology:
Strategies and Economic Tools
There is little point in trying to preserve natural populations of individual species if their habitats are in jeopardy
Habitat Protection includes:
Preservation enforces strict land use, sometimes precluding human use
Mixed-use conservation protects some areas and controls development in others
Restoration re-establishes vitality of community or ecosystem
Preservation
Mixed-Use Conservation
When complete preservation is impractical, conservationists advocate mixed-use conservation, which combines protection of some land parcels with controlled development of others
Ngorongoro Conservation Area (NCA), Tanzania
Ngorongoro Conservation Area
Restoration
Conservation biologists sometimes create restoration plans to reestablish a previously disrupted community or ecosystem
Restoration requires the removal of contaminants, impediments to the natural flow of water, and barriers to animal movement – as well as restoration of natural processes, such as periodic fires or floods
Most restoration projects also require replanting key plant communities and long-term management after restoration
Brazilian Atlantic Forest: Restoration
Economic Factors
To be successful, a conservation plan must be economically feasible and provide direct benefits to local residents whose lives it will affect
Conservation plans are more successful if they provide local residents with benefits that depend on the existence of a preserve
The Chitwan National Park, Nepal
originally a hunting ground for local royalty
Today, humans are excluded from the park for most of the year
Chitwan National Park, Nepal
Ecotourism
In some preserves, governments enlist local residents in park operations, providing them with a viable livelihood
The most successful approach has been ecotourism in which visitors, often from wealthier countries, pay to visit a nature preserve where local people work
Critics note that increased human (and automobile) traffic degrades protected habitats – and unregulated ecotourism can eventually lead to overdevelopment
Ecotourism in Costa Rica
http://www.costarica-ecotourism.com/
Ecosystem Valuation
In the mid-1990s, conservation biologists and economists developed the concept of ecosystem valuation, in which ecosystem services are assigned an economic value
The global value of ecosystem services has been estimated around $33 trillion – almost twice the value of all goods produced by all humans on the planet
Ecosystem Services & Intrinsic Worth
An Increase in Extinction Rates
Background extinction rates eliminate a few species per year
At least five mass extinctions appear in the fossil record
The greatest mass extinction of all time is occurring now at 1,000 times background rate
What should we do?
Should we act to stop the loss of biodiversity?
If the land mechanism as a whole is good, then every part is good, whether we understand it or not. If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering.
Aldo Leopold, 1953
Should we act to stop the loss of biodiversity?
How realistic is it to try to save every species?
If we can’t save every species, then what do we save and what do we let go?
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