Seven major threats to biodiversity that result from
human activity
1)
2)
3)
4)
5)
6)
7)
habitat destruction
habitat fragmentation
habitat degradation and pollution
global climate change
overexploitation of species for human use
introduction of exotic species
increased spread of disease
Overexploitation
-even in pre-industrial societies, overexploitation led to the decline and
extinction of species
Exs. 1) Pleistocene Overkill Hypothesis
-about 3/4 of megafauna (44 kg or100 lbs) became extinct shortly after
human arrival on several continents (Australia, South America, North
America) (Martin and Klein, 1984 Quaternary Extinctions: A
Prehistoric Revolution)
2) mamo bird of Hawaii was used to make cloaks for kings that required
70,000 birds of this now extinct species
Overexploitation
-some traditional methods of hunting and harvesting are sustainable
because the people placed restrictions on the harvest
-as technology increased, overexploitation has increased and threatens
many vertebrate species. Ex. Intensive harvesting of fish Fig. 10.1
-in Africa there is a bushmeat crisis as populations of mammals are
reduced 80% by intensive hunting so the meat may be sold
-today, the worldwide trade in wildlife is valued at over 10 billion dollars
per year (excluding timber (75 billion) and fish (100 million tons per
year)
10.1 Intensive harvesting has reached crisis levels in many of the world’s fisheries
10.2 Bushmeat hunters begin with the largest animals, then remove medium and small animals
Some examples of overexploited organisms:
1) bison
2) seahorses in China are used in traditional medicine because it resembles
a dragon and is believed to have great healing power (45 tons or 16
million seahorses per year)
3) threatened and endangered plants that are collected in the wild for
horticultural use (cacti, orchids, carnivorous plants) and medicinal
uses like Neopicrorhiza (Scrophulariaceae) Fig. 10.3
4) many species of fish in the North Atlantic. Ex cod off Newfoundland
declined to 1% of their original numbers and the Canadian government
closed fisheries in 1992 eliminating 35,000 jobs
Fig. 10.4
5) Endangered whales Box 10.1
10.3 Neopicrorhiza is a Himalayan medicinal plant that is declining rapidly due to overharvesting
Figure 10.4 Trophy fish caught in Key West, Florida. Note modern losses in size and abundance.
Box 10.1 (Part 1) Worldwide populations of whale species harvested by humans
Box 10.1 (Part 2) Japanese whalers harpooning a minke whale near Antarctica, supposedly for
scientific research, but the meat will be sold.
Possible Solutions to overexploitation
Invasive species
-species that increase in abundance at the expense of native species
-often exotic species, which are species that occur outside their natural
ranges because of human activity
-invasive exotic species threaten about 40% of endangered species in
USA with damages and losses totaling 120 billion per year
Common water hyacinth,
an invasive, exotic plant
10.7 Two accidentally introduced exotic species in US-gypsy moth (silk, but escaped) & R.I. fire ant
Many introduced species (exotic species) have occurred by the following
means:
1. purposeful introductions that got out of control:
a) Settlers arriving at new colonies introduced hundreds of species of
mammals, birds, and fish to make the countryside more familiar and
provide game and fish
b) Large numbers of plants were introduced as agricultural or ornamental
species as well as soil stabilizers
Ex. salt cedar was introduced for erosion control and now displaces
native vegetation along waterways
c) Genetically modified organism (GMO) Box 10.2
Box 10.2 GMO crops
2. Some examples of accidental introductions:
a) numerous species of marine organisms in ship ballast water
b) 100s of weed species in the USA with many being aggressive invaders
c) fire ants that negatively affect quail populations
10.8 Northern bobwhites in Texas have been declining following the arrival of the exotic red fire ant
3. biological controls that got out of hand:
-use of one organism to control another organism
A few examples
a) parasitic fly introduced to control gypsy moth (introduced for silk
production) that feeds on timber trees has been found to parasitize
more than 200 native moth species
b) flower head weevil was introduced in Canada and the USA to eliminate
introduced species of thistle. It now is parasitizing native thistles
c) cane toad was introduced to Australia to eliminate sugar cane beetles.
They have grown to plague proportions and are decimating all sorts of
native Australian invertebrates
Invasive species on islands
-isolation of islands often leads to endemism but it also leaves species
vulnerable to introduced invasive organisms
Three examples illustrate effects of introduced species on islands:
a) feral pigs and goats caused 48 plant species to be lost on Santa Catalina
Island
b) brown tree snake introduced to Pacific islands via packing crates eats
eggs, nestlings, and adult birds. In Guam, it has driven 10 of 13 forest
birds extinct Fig. 10.9
c) cannibal snail was brought into Society Islands in the Pacific to displace a
garden pest called the giant African snail. It has eliminated 50 species of
land snails from the islands
10.9 The brown tree snake is introduced and devastates populations of endemic birds
Invasive species in aquatic habitats
-freshwater communities are often isolated habitats similar to islands and
often, like islands suffer severely from the introduction of invasive
species
-large numbers of estuarine fish species, often in ballast water
-1/3 of worst invasive aquatic species are from aquarium and
ornamental species traded worldwide to bring in about 25 billion
dollars
Some examples:
a) Sea lampreys in Great Lakes cost 13 million/year to control so that
they do not damage sport and commercial fishing
b) zebra mussel- stowaway on ships from Caspian Sea (west Turkey and
Iraq) that was introduced to Great Lakes. Ex. Lake Erie has
700,000/square meter in some areas and the cost to keep water intake
pipes clear may cost over 3 billion over the next 10 years Fig. 10.10
c) North American coastal comb jelly transferred by ballast to Black Sea
in eastern Europe in 1982. By 1989 it comprised 95% of biomass
collapsing a $250 million fishing industry and marine ecosystem
10.10 Zebra mussel and Quagga mussels encrusting a current meter and their distribution
10.6 In Flathead Lake, Montana and its tributaries, the food web was disrupted by the intentional
introduction of opossum shrimp for salmon food. It ate huge #s zooplankton disrupting food web.
Why do exotics become invasive?
-most introduced species do not survive outside their native habitats and
less than 1% become invasive. Invasive exotics occur because of the
following:
1) Absence of natural predators and parasites in the new habitat
2) May hybridize with a closely related native species causing extinction
of the native species because it swamps the gene pool of the native
species
3) Able to tolerate disturbed conditions better than native species.
Highest numbers of invasive exotics occur in habitats most altered by
human activity
What can be done to slow invasive exotics.
1. Removal and restoration has been done in many protected natural
areas. The National Park Service considers invasives to be the most
serious threat to their ecosystems Figure 10.11
2. Reduce the rate of their introduction by passing laws and custom
restrictions prohibiting the transport and introduction of exotics Figure
10.12
10.11 Remove exotics (European Beach brass) and ecosystems recover-Humboldt Bay NWR, CA
10.12 Strategy to reduce the impact of harmful invasive species--Asian beetle that kills native trees
Disease
-caused by microparasites -viruses, bacteria, fungi, and protozoans OR
macroparasites - flatworms, roundworms, helminth worms, parasitic
arthropods, parasitic plants
-transmission of disease has increased because habitat destruction may
increase disease-carrying vectors and interactions with domestic
animals and people have spread diseases into native species
Three practical implications for management of rare species:
1) High rate of contact between the host and parasite increases the spread
of disease
-especially a problem in confined situations such as habitat fragments,
zoos, and parks
2) Indirect effects of habitat fragmentation and degradation can increase
the susceptibility to disease.
-deterioration of habitat quality stresses organisms lowering disease
resistance Fig. 10.15
Ex of combined effects #1&2. Texas in the mid-eighties had increased
winter deaths of sandhill cranes. In 1984-85, 5000 birds died during
the winter. They were eating unharvested, rotting peanuts infected
with a fungus. Now plowed under.
10.15 Infectious diseases spread triggered by habitat fragmentation and degradation
Three practical implications for management of rare species (cont.):
3) In conservation areas and zoos, species may contract diseases from
related species and even humans.
Ex Tanzania's Serengeti National Park- Lions (25%) are infected by
canine distemper (viral) from contact with the 30,000 domestic dogs
near park
Ex. Canine distemper also destroyed the last population of black-footed
ferrets in the wild
Ex. North American chestnut trees, once common in the eastern USA are
almost all gone due to an ascomycete carried by Chinese Chestnut
trees imported to New York City. Fungal diseases are also eliminating
elm trees, oaks, and flowering dogwoods from ecosystems Figure
10.14
10.15 Populations of flowering dogwood are declining in eastern North American because of
anthracnose disease caused by an introduced fungus
Problems with disease may be reduced by: