Seven major threats to biodiversity that result from human activity
-these threats stem from human population growth
Figure 9.1, Table 9.1
9.1 Human activities create multiple threats to biological diversity
-100 million/year is the estimated growth of the human population
-more people = less biodiversity
-population growth is not the only cause, overconsumption of resources is also
responsible. Mostly done by a wealthy minority in developing countries
and those in developed countries
Ex. USA has 5% world’s population but consumes 25% resources
USA produces a large ecological footprint = number of hectares (1 ha=2.5
acres) of land required to support the lifestyle of a single person
-not sustainable in the long run. If this pattern is adopted by the expanding
middle class in the developing world it will cause massive environmental
destruction Figures 9.2 & 9.3 & 9.4
9.2 An ecological footprint for a nation is the number of global hectares needed to support an average citizen
9.3 Threats to the world’s species
9.4 Many of the world’s major biomes have had a large proportion of their area converted to human
use. Temperate forests are expected to gain because of abandoned farms in these areas.
Habitat destruction:
1) Tropical rain forest
-large losses of forest habitat Ex. Table 9.2
-tropical rain forests cover 7% of earth's surface and contain 50% of
its species
-Loss of about 1% of original area of Tropical rain forest per year
-60% of rain forest destruction results from shifting cultivation (slash and
burn agriculture) Figures 9.5 & 9.6
-20% is lost to commercial logging
-10% is lost due to clearing to establish cattle ranches
-remaining percent is lost due to: 1) cash crop plantations such as oil
palm, cocoa, and rubber; 2) road building; 3) mining
9.5 Displacement of rain forest for agricultural purposes—Shifting cultivation; aka slash and burn
9.6 Due to intensive agriculture, rain forest has been declining rapidly in South America
Habitat destruction
2) Tropical deciduous forest
-large losses also Ex. < 2% of original extent of dry forest left on Pacific Coast
of Central America and only 3% in Madagascar, where lemurs are
endangered Fig. 9.7
-better ranching country and there is a 5X greater human population density in
Central America than in the adjacent rainforest
9.7 One species of lemur, a lineage of primates found only on the large island of Madagascar
Habitat destruction
3) Grasslands
-most are gone as they are easy to convert to farmland and rangelands are
often overgrazed
Ex. 97% tall grass prairie of North America converted to farmland
Temperate grasslands are valuable for protecting biodiversity—National Bison Range, Montana
Grasslands are an important biome for ranching
If ranchers overgraze, the grassland ecosystem is destroyed.
Habitat destruction
4) Wetlands and aquatic habitats
-during the last 200 years, 1/2 of wetlands in the USA have been destroyed
-tropical wetlands often dominated by mangroves have been decimated in
some areas Ex. 15% mangrove communities in SE Asia have been
destroyed to make room for aquaculture of rice and shrimp
Habitat destruction
5) coral reefs
-20 % of all coral reefs have been destroyed
-90 % in the Philippines
-losses of coral reefs are mainly due to
1) pollution that often causes algal blooms that when they die off and
decay, remove oxygen from water killing reef life
2) sedimentation following deforestation
3) Overharvesting
Fig. 9.9
9.9 Extensive areas of coral will be damaged or destroyed without conservation measures
Habitat destruction
A variety of habitats around the world have been degraded into man-made
deserts = desertification
-not functional desert ecosystems but wastelands
-loss of soil gives the area the appearance of deserts
-initially these areas supported agriculture but during dry and windy years,
soil erosion and loss of the water holding capacity of the soil occurs
-overgrazing and cutting forests for fuel often start the process of
desertification
Fig. 9.10
9.10 Arid areas of the world are experiencing encroaching desertification (Part 1)
Habitat fragmentation
Habitat fragmentation
-process where large areas of continuous habitat is reduced in area
creating fragments of habitat Figures 9.11 & 9.12
Differ from the original habitat in two ways
1) fragments have a greater amount of edge per area of habitat
2) center of each habitat is closer to an edge Figure 9.13
9.11 Forested areas of Tropical Asia have experienced fragmentation due to deforestation
Sumatra, a large island in Indonesia
9.12 Rural development of the road network in Colorado causes habitat fragmentation
9.13 Habitat area is severely reduced by fragmentation and edge effects
Habitat fragmentation
Consequences of habitat fragmentation
1) Certain species may not have enough room to live and breed Figure
9.14
2) potential for dispersal and colonization is often reduced
3) reduces foraging ability of animals
4) increases rate of population decline and extinction by dividing an
existing widespread population into two or more subpopulations that
are more vulnerable to inbreeding depression and genetic drift (allele
frequencies changing by chance) Figure 9.16
5) Edge effects-changes in microclimate, incidence of fire, interspecific
interactions, and potential disease along fragment edges
9.14 The probability of sighting a wood thrush in a mature forest in Maryland
9.16 (A) Former wild reindeer herds in southern Norway; (B) The range has now been divided
Habitat fragmentation
Edge effects
a. microclimate changes
1. temperature varies more (hotter in day and cooler at night)
2. light and wind are greater
3. humidity is less
b. increased incidence of fire because of microclimate changes
c. interspecific interactions
increases chances for invasion by exotic and native pest species
1. wind dispersed seeds and fruits Ex. Asteraceae
2. omnivorous animals that respond well to disturbance
Ex. raccoons, skunks, bluejays
3. predators that like disturbance and decimate
amphibian and insect populations Ex. coyotes
4. herbivores that like disturbance Ex. deer
d. greater potential for disease due to increased contact with domestic
organisms
Figure 9.15
9.165 Edge effects in the Amazon Rain Forest
Habitat degradation and pollution
Several major categories:
1) Pesticide pollution
Rachel Carson Silent Spring 1962
-described biomagnification-chemicals move through the food chain
becoming more concentrated at each level Figure 9.19
-raptors such as the American bald eagle, osprey, and peregrine falcon
were particularly susceptible
-inactivate enzymes and other proteins
-banned the use of organochlorine compounds (Ex DDT
diphenyltrichloroethane) in this country
-more details are available in Box 9.1
9.19 Toxic chemicals in water become successively concentrated at higher levels in the food chain
Box 9.1 A captive peregrine feeding young affected by DDT
Box 9.1 Peregrine populations have gradually recovered after DDT banned along with population
augmentation and nest protection
Habitat degradation and pollution
2) Water pollution
Several major problems:
a. cultural eutrophication
-human sewage, fertilizers, detergent, and industrial processes that release
large amounts of nitrates and phosphates cause algal and cyanobacteria
blooms. This shadows bottom dwelling plants and algae and if their is
a rapid die-off, oxygen is removed from the water during the process
of decomposition. Figure 9.20
9.210 Fish in Rio de Janeiro died off as a result of eutrophication
Habitat degradation and pollution
b. influx of eroding sediments
-kills plant and algae populations and clogs filter feeding adaptations in
invertebrates Ex. coral
c. oil products
-blocks light from algae and plants and clogs tissues involved in gas
exchange and filter feeding
Figure 9.17
d. heavy metals and other types of chemical pollution
-inactivate enzymes and other proteins (cytochromes)
e. destruction of bottom habitat and sediment resuspension caused by
trawling
Figure 9.18
9.17 Marine birds after the Deepwater Horizon oil spill.
9.18 The aquatic environment faces multiple threats
Habitat degradation and pollution
3) Air pollution
Several major problems:
a. acid rain
-nitrates and sulfates from burning fossil fuels combines with water in the
atmosphere lowering the pH of rain Figure 9.21, 9.22
-lowered pH changes enzyme activity and other proteins
9.21 Mountain forests near power plants & industry have acid rain— Bavarian Forest in Germany
9.22 The pH scale, indicating ranges at which acidity becomes lethal to fish
Habitat degradation and pollution
b. ozone production and nitrogen deposition
-hydrocarbons and nitrogen oxides react and produce ozone and airborne
nitrogen compounds
-high levels of ozone damage tissue (oxidize them and make them brittle)
-airborne nitrogen compounds are deposited by rain and if this is
excessive contributes to eutrophication
-ozone in the upper atmosphere helps to filter ultraviolet radiation and
deposition of air borne nitrogen compounds created by lightning is a
part of the nitrogen cycle
Habitat degradation and pollution
c) toxic metals
-leaded gasoline (used outside the USA) and industrial processes (mining
and smelting) release lead, zinc, and other toxic metals into the air.
These inactivate enzymes and other proteins in living things
Global Climate Change
-caused by increases in greenhouse gases--carbon dioxide, methane,
water, and nitrous oxide Figure 9.24
-greenhouse gases keep the earth warm and allows for life as we know it
9.24 The greenhouse effect (Part 1)
Global Climate Change
-levels of greenhouse gases have increased over the past 100 years Figure
9.25, Table 9.3
-if this trend continues, greenhouse gases could cause global temperatures
to increase (2-6 degrees Celcius) by 2100 Figure 9.26
9.25 Carbon emissions from fossil fuel use and forest destruction has increased dramatically
9.26 Computer models of global climate predict that temperatures will increase significantly
Global Climate Change
If the temperature rises, the following changes would occur in temperate
and tropical climates:
1) Rising sea levels
-mountain glacier and polar ice caps melting could cause sea levels to rise
20-60 centimeters over next 100 years and flood some coastal
communities Fig. 9.27
2) Warmer waters
-this along with pollution, and spread of disease is killing coral
2) Radical reconstruction of communities and changes in range for
species
-will need to evaluate protected natural areas and provide more along
elevational gradients and north-south migration routes Fig. 9.29
Figure 9.27 (A) The result 1-m sea level rise by the end of this century. (B) Result of a 3-m rise
9.29 Protected areas along elevational gradients are needed