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Conservation Biology Chapter 59

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Biodiversity Crisis •  Extinction is a fact of life: all species

become extinct eventually •  More than 99% of species known to

science are now extinct •  Current accelerating loss of habitat

– 20% of present day species will be extinct by the middle of this century

– 2000 of the world’s 8600 species of birds could go extinct

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Biodiversity Crisis

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Biodiversity Crisis •  The majority of recent extinctions have

occurred in the past 150 years •  Increased rate of extinction is worsening •  Half of Earth’s plant species may be

threatened •  2/3 of vertebrate species could perish by

the end of this century

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Biodiversity Crisis •  Majority of extinctions have occurred on

islands – Of 85 species of mammals; 60% lived

on islands •  Why are islands so vulnerable ?

– Evolved in the absence of predators – Humans introduced competitors,

diseases – Island populations are usually small

which increases their risk for extinction

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Biodiversity Crisis •  Current mass extinctions are notable

because – It is the only such event triggered by a

single species (Homo sapien) – A few million years is a long time to wait

for recovery – It is not clear that biodiversity will

rebound this time •  Humans are utilizing resources that new

species would need to evolve

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Biodiversity Crisis •  Endemic species: species found

naturally in only one geographic area and no place else – Occupy restricted ranges – Example: Komodo dragon lives only

in a few islands – Example: Mauna Kea Silversword

only lives in a single volcano crater on the island of Hawaii

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Biodiversity Crisis

Some species under imminent extinction threat

Silversword

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Biodiversity Crisis

Hotspots: areas where species have high endemism and are disappearing at a rapid rate. Red areas are hotspots.

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Biodiversity Crisis

25 hotspots have been identified Contain nearly half of all terrestrial

species in the world

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Biodiversity Crisis •  Human population growth in hotspots •  By protecting 1.4% of the world’s land

surface –  44% of the worlds vascular plants –  35% of its terrestrial vertebrates can be

preserved •  In 1995, 20% of the human population

were located in hotspots •  Growth rate exceeds the average in 19

hotspots

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Biodiversity Crisis

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Biodiversity Crisis Why are species going extinct in hotspots ? •  High rates of habitat destruction

– Land cleared for agriculture, housing, economic development

•  More than 70% of the original area of each hotspot has already disappeared

•  Only 15% or less of original habitat remains in 14 hotspots – 90% Madagascar forest lost – 95% Brazilian forest lost

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Value of Biodiversity •  Why care about loss of biodiversity ?

– Direct economic value of products we obtain from species: food and drugs

– Indirect economic value of benefits produced by species without our consuming them

– Ethical and aesthetic values

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Value of Biodiversity •  Direct economic value includes

resources for our survival – Food crop genetic variation – 40% of prescription and

nonprescription drugs have active ingredients extracted from plants • Aspirin • Cancer fighting drugs

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Value of Biodiversity •  Rosy Periwinkle:

vinvlastine and vincristine effectively treat common forms of childhood leukemia – Increase chances

of survival from 20% to over 95%

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Value of Biodiversity

Cancer-fighting drugs like taxol, have been developed from the bark of the Pacific yew

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Value of Biodiversity •  Indirect economic value is derived from

ecosystem services – Maintain chemical quality of natural

water, buffer against storms and droughts – Prevent loss of minerals and nutrients – Moderate local and regional climate – Absorb pollution – Promote breakdown of organic wastes

and cycling of minerals

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Value of Biodiversity

Tropical rainforests provide more economic benefits if they are left standing than if they are destroyed and the land used for other purposes

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Value of Biodiversity •  Economic trade-offs

– Ecosystem was beneficial when the United States was being settled

– Habitat destruction today may be economically desirable • How many services will it provide • What are the negative effects

– Increased flooding and pollution – Decreased rainfall – Vulnerability to hurricanes

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Value of Biodiversity •  Consequences of removing a species

could mean we are gambling with the future of an ecosystem we depend on

•  Problems of valuing ecosystems – Do not have a good estimate of the

monetary value of services provided by ecosystems

– People who gain the benefits of environmental degradation are often not the same people who pay the costs

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Value of Biodiversity •  Ethical and aesthetic values are based

on our conscience – Every species has a value of its own – Humans should act as guardians or

stewards for the diversity of life around us

– How do we place a value on beauty ? • What if it no longer existed ?

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Factors Responsible •  Causes of extinction: direct or indirect

– Overexploitation – Habitat loss – Introduced species – Disruption of ecosystem interactions – Pollution – Loss of genetic variation – Catastrophic disturbances

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Factors Responsible

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Factors Responsible •  Habitat loss devastates species

richness •  Natural habitats may be adversely

affected by humans 1.  Destruction 2.  Pollution 3.  Disruption 4.  Habitat fragmentation

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Factors Responsible •  Destruction of habitat

– Clear-cut harvesting of timber – Burning of tropical forests – Urban and industrial development

•  10 fold increase in habitat area leads to ~ doubling in the number of species

•  Area reduced by 90% then half of all species will be lost

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Rain forest covering the eastern coast of Madagascar: •  90% habitat loss •  many extinctions •  16 of 31 primate species threatened or extinct

Factors Responsible

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Factors Responsible •  Pollution

– Species can no longer survive – Aquatic environments particularly

vulnerable – Many lakes “sterilized” by acid rain

•  Disruption – Visitors to bat cave: four visits per

month caused 86% - 95% declines in population size

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Factors Responsible •  Habitat fragmentation: dividing the

habitat up into small, unconnected areas – Low population numbers – Smaller populations in each fragment – Edge effects: changes in

microclimate along the edge of a habitat

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Factors Responsible •  Edge effects

– Trees exposed to more sunlight • Hotter and drier conditions • Less biomass growth

– Opportunities for parasite and predator species

– Habitat fragmentation is blamed for local extinctions in a wide range of species

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Factors Responsible

•  Fragmentation of Wisconsin woodland habitat

•  Cover less than 1% of original area

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Factors Responsible •  Landowners in Manaus, Brazil

preserved patches of rain forest of different sizes to examine the effect of patch size on species extinction

•  Extinction rate was negatively related to patch size

•  Even the largest patches (100 hectares) lost half of their bird species in less than 15 years

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Factors Responsible Introduced species threaten native species

and habitats •  Colonization: process by which a species

expands its geographic range – Birds are blown off course – Bird eats a fruit and defecates its seeds

miles away – Lowered sea levels connect to isolated

populations

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Factors Responsible •  Colonization brings together species with

no history of interaction •  Ecological interactions may be strong

because species have not evolved ways of adjusting to the presence of one another

•  Results: – Increase in species diversity – Extinction of species

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Factors Responsible •  Human influence on colonization

– Plants and animals can be transported in the ballast of large ocean vessels

Zebra mussels

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Factors Responsible •  50,000 species have been introduced in the

United States •  Effects:

– $140 billion per year in economic costs – Human health: west nile fever – Hawaii: mosquitoes brought malaria

• 70% native fauna extinct or restricted to high elevations

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Factors Responsible

Two thirds of Hawaiian birds are extinct or have reduced populations

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Factors Responsible •  Effect may not be direct, but spread

through the ecosystem – Argentine ant has spread through

much of the southern US, reducing populations of native ant species • Negative effect on coast horned

lizard which feeds on native ants • Native ants spread seeds,

introduced ones do not

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Factors Responsible •  Efforts to combat introduced species

– Eradicating extremely difficult, expensive and time consuming

– Prevent introduction

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Factors Responsible Disruption of ecosystems can cause an extinction cascade

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Factors Responsible •  Loss of keystone species may disrupt

ecosystems – Sea otters are a keystone species of kelp

forest ecosystems – Keystone species is a qualitative concept – Flying fox bats are a keystone species

• Pollinates plants • Key disperser of seeds • Elimination due to hunting and habitat

loss is having a devastating effect

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•  Small populations are vulnerable to extinction – Demographic factors

• Ill-equipped to withstand catastrophes • Heath hen

– Once common in US: hunting pressure eliminated all but 1 population

– Fire destroyed the preserve’s habitat – Population ravaged by predators

Factors Responsible

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Factors Responsible •  Lack of genetic variability is a second

dilemma small populations face – Genetic drift

•  Populations lacking variation composed of sickly, unfit or sterile individuals

•  More genetically variable individuals have greater fitness

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Factors Responsible •  Tested genetic variation theory

– Extracted DNA for stuffed birds collected in 1930s

– Compared to birds living in the same place before 1970 population collapse

– Genetic variation loss in population in Illinois

– Transplant birds from other states – Hatching rates back up to 94% in 1994

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Preserving Species Destroyed habitats can sometimes be restored

• Restore plants and animals to abandoned farm lands

• No restoration is ever truly pristine

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Preserving Species Removing introduced species •  Cichlid fishes restoration

– Breeding and restocking endangered species

– Removal of water hyacinth and Nile perch populations

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Preserving Species Cleanup and rehabilitation •  Clean up pollution •  Nashua River in New England

– Heavily polluted habitat – Returned to near pristine condition

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Preserving Species

Case Study: Peregrine falcon

•  DDT banned in 1972 – Captive breeding

program began in 1970

– 1986: over 850 birds released in 13 states

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Conservation of Ecosystems •  Habitat fragmentation is one of the

most pervasive enemies of biodiversity conservation efforts

•  Focus on preserving pristine state in national parks and reserves – Amount of land preserved is limited – Not many areas completely protected

•  Also focus on surrounding areas with some level of human disturbance

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Conservation of Ecosystems •  Key to management

– Operate them in a way compatible with local land use • No economic activity in core pristine

area • Remainder of land used for

nondestructive harvesting of resources • Some hunting • Corridors of dispersal

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Conservation of Ecosystems •  Corridors of dispersal

– Link pristine areas – Increase population sizes – Allow recolonization due to

catastrophe – Protection to species that move over

great distances during the course of a year

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Conservation of Ecosystems