Seven major threats to biodiversity that result from human activity 1) habitat destruction2) habitat fragmentation3) habitat degradation and pollution4) global climate change5) overexploitation of species for human use6) introduction of exotic species7) 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: