1. Threats to Biodiversity
Chapter 43
Threats to Biodiversity

2. You Must Know How human actions are changing the Earth.

3. Overview Biologists estimate 10–100 million species exist on Earth.
Scientists have named and described 1.8 million species. Biologists estimate 10–100 million species exist on Earth. Tropical forests contain some of the greatest concentrations of species and are being destroyed at an alarming rate. Humans are rapidly pushing many species toward extinction. Rates of species extinction are difficult to determine under natural conditions. Extinction is a natural process, but the high rate of extinction is responsible for today’s biodiversity crisis. Human activities are threatening Earth’s biodiversity. (You don’t need to memorize the names of the time periods.)
Extinction rates my be greater than they were at the close of the cretaceous. 3

4. Biodiversity has three main components Genetic diversity
Species diversity
Ecosystem diversity 4

5. Genetic diversity in a vole population
Genetic diversity comprises genetic variation within a population and between populations.
Genetic diversity in a vole population
Genetic diversity in a different vole population
Population extinctions reduce genetic diversity, which in turn reduces the adaptive potential of a species. 5

6. Processes driving an extinction vortex
Small population
Inbreeding, genetic drift
Lower reproduction, higher mortality
Loss of genetic variability
Lower individual fitness and population adaptability
Cavendish Banana
Smaller population 6

7.
Illinois had millions of greater prairie chickens in the 19th century but fewer than 50 by 1993.
200
150
100 50
1970
1975
1980
1985
1990
1995
Translocation
Year
(a) Population dynamics
Number of male birds
Eggs hatched (%) 90 80 70 60 40 30
Years
(b) Hatching rate
1970–’74
’75–’79
’80–’84
’85–’89
’90
’93–’97
Populations of the greater prairie chicken in North America were fragmented by agriculture and later found to exhibit decreased fertility. To test the extinction vortex hypothesis, scientists imported genetic variation by transplanting birds from larger populations. The declining population rebounded, confirming that low genetic variation had been causing an extinction vortex. 7

8. Figure
Genetic diversity in a vole population
Species diversity in a coastal redwood ecosystem
Species diversity is the variety of species in an ecosystem or throughout the biosphere. 8

9. The local extinction of one species can have a negative impact on other species in an ecosystem.
Four-fifths of the tree species in the Samoan Islands depend on flying foxes for pollination or seed dispersal.
Keystone Species
Over harvesting
Flying foxes (bats) are important pollinators and seed dispersers in the Pacific Islands 9

10. Genetic diversity in a vole population
Figure
Genetic diversity in a vole population
Species diversity in a coastal redwood ecosystem
Human activity is reducing ecosystem diversity, the variety of ecosystems in the biosphere. More than 50% of wetlands in the contiguous United States have been drained and converted to agricultural or other use.
Community and ecosystem diversity across the landscape of an entire region
Ecosystem diversity is the variety of ecosystems in the biosphere 10

11. * Ecosystem Services Some examples of ecosystem services
Purification of air and water
Crop pollination, pest control, and soil preservation
Ecosystem services have an estimated value of $33 trillion per year, but are provided for free
Ecosystem services encompass all the processes through which natural ecosystems help sustain human life * 11

12. Threats to Biodiversity
Habitat loss
Introduced species
Overharvesting 12

13. Biogeographic factors affect community diversity
Island Biogeography and the Species-Area Curve
The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more species. Species richness on islands depends on island size, distance from the mainland, immigration, and extinction.
The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at a dynamic equilibrium point. Conservation biologists apply understanding of landscape dynamics in establishing protected areas to slow the loss of biodiversity. 13

14. “Islands”

15. Corridors Can Connect Habitat Fragments
A movement corridor is a narrow strip of habitat connecting otherwise isolated patches. Movement corridors promote dispersal and reduce inbreeding. Corridors can also have harmful effects, for example, promoting the spread of disease. In areas of heavy human use, artificial corridors are sometimes constructed.
Movement corridors promote dispersal and reduce inbreeding

16. Habitat Loss and Fragmentation
Human alteration of habitat is the greatest threat to biodiversity throughout the biosphere. In almost all cases, habitat fragmentation and destruction lead to loss of biodiversity. The boundaries, or edges, between ecosystems are defining features of landscapes. Some species take advantage of edge communities to access resources from both adjacent areas. Landscapes dominated by fragmented habitats support fewer species due to a loss of species adapted to habitat interiors.
Cowbirds 16

17. Introduced Species
Introduced species are those that humans move from native locations to new geographic regions. Without their native predators, parasites, and pathogens, introduced species may spread rapidly. Introduced species that gain a foothold in a new habitat usually disrupt their adopted community.
Nutria were introduced to the Louisiana ecosystem in the 1930s, when they escaped from fur farms that had imported them from South America. Nutria have since become pests in many areas, destroying aquatic vegetation, marshes, and irrigation systems, and chewing through human-made items, such as tires and wooden house paneling in Louisiana, eroding river banks, and displacing native animals 17

18. Human activities are transporting pathogens around the world at unprecedented rates.
American Chestnut
Ecological communities are universally affected by pathogens, disease-causing organisms and viruses.
The American chestnut, Castanea dentata, is a large tree of the native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range. There are now very few mature specimens of the tree within its historical range, although many small shoots of the former live trees remain. However, there are hundreds of large (2 to 5 ft diameter) trees outside its historical range, some in areas where less virulent strains of the pathogen are more common. 18

19. Overharvesting
Species with restricted habitats or large body size with low reproductive rates are especially vulnerable to overharvesting
Overharvesting is human harvesting of wild plants or animals at rates exceeding the ability of populations of those species to rebound. 19

20. *