Download Amphibian decline case study

Amphibian decline case study
 1963, many breeding bright orange toads (Bufo periglenes)
 1989, only a single male was observed
 Today, the toads have gone extinct
Amphibians in trouble
 Frog populations that had once been abundant were now decreasing or
entirely gone
 In 2005, evidence that 43% of amphibian species experienced decreases in
population size
 1/3rd are threatened with extinction
Number of threatened species
Why worry about amphibian declines?
 Many species have declined in pristine, well-protected habitats
 Particularly sensitive to the state of the environment because of their moist
skin
 Chemicals pass into their body
 Larvae are aquatic, adults are terrestrial
 No single cause for amphibian decline is apparent
Types of habitat destruction
 Destruction
 Pollution
 Disruption
 Fragmentation
Rainforest in Madagascar
 90% habitat loss
 16 of 31 primate species threatened or extinct
Extinction is related to area
Habitat degradation
 Reduction in the quality of available habitat
 Pollution
 Bald eagle
 Disruption
 Fragmentation
 Neotropical migrants
Disruption
 Four visits by visitors to bat cave per month caused 86% - 95% declines in
population size
 Human activities can have ramifications throughout the food chain
 In Alaska, otter numbers have fallen 90% since the 1970s due to
overharvesting of whales
Deforestation and fragmentation in WI
Fragmentation research
Edge effects
 Ecological/biotic influences which occur within areas of “natural habitat” in
close proximity to modified habitats
 Includes changes in microclimate, predation, invasion of exotics (particularly
weedy species), and human disturbance
Neotropical migrants
Songbird decline
 Migrant songbirds have declined
 Nest in northern forests in summer but spend winter in South or Central
America or the Caribbean Islands
 Caused by habitat fragmentation and loss in summer and wintering areas
Overexploitation
 37% of all endangered, vulnerable and rare species of vertebrates are
threatened by overexploitation
 Fur-bearing animals (giant otter, most species of cats)
 Elephants (for ivory)
 All species of rhinoceros (for aphrodisiacs)
Whaling
“The Passenger Pigeon needs no protection. Wonderfully prolific, having the
vast forests of the north as its breeding grounds, traveling hundreds of miles in
search of food, it is here today, and else-where tomorrow, and no ordinary
destruction can lessen them or be missed from the myriads that are yearly
produced.”
Committee report on the game bill to the State Legislature of Ohio, 1857
Bushmeat
Invasive species
 Plants, animals and other organisms that establish themselves in new
ecosystems and are able to reproduce, spread and persist to the detriment of
the native environment
Invasive species
 Invasive species threaten 19% of all endangered and vulnerable species
 Greatest impact on islands
 Impacts through predation, competition, and/or habitat modification
Economic impacts of invasive species
 Cause economic damage - $140 Billion per year in United States
 Decreased yield and quality in agriculture, forestry and fishing
 Disrupts waterways and limits opportunities for boating and recreation
 Cost of prevention and control
How do they get here?
 Humans have greatly increased colonization rates
 Intentional introduction - intended for use in agriculture, horticulture,
medicine, or erosion control
 Accidental - stowaways in ballast on ships and as contaminants in imported
materials
Mongoose
 Released in Hawaii to control rats
 Rats are nocturnal and Mongooses are diurnal
 Both are now problems
Asian tiger mosquitoes
 Arrived on container ships carrying used tires
 Spread West Nile Virus
Hawaiian birds
Effects may not be direct
 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
Small populations
 Some species have been reduced to small numbers
 Small numbers of species are prone to extinction due to
 Demographic factors
 Genetic factors
 The interaction of these two factors
Demographic factors
 Random event
 Skewed sex ratios
 Allee affect
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
Illinois prairie chicken
Inbreeding depression in alleviated by managers adding new chickens to
population
Restoration ecology
 Restoration ecology seeks to repair or reconstruct ecosystems damaged by
humans or natural forces
Tools of restoration
 Horticultural or animal control methods
 Removal of invasive species
 Seed broadcasting
 Fire
 Let nature heal itself
Captive breeding
 Breeding programs in zoos and botanical gardens are one method of saving
threatened species
 Most mammals in North American zoos are now produced from captivebreeding programs
 Many zoos now participate in reintroduction programs
Peregrine falcon
Conservation of ecosystems
 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
Management of ecosystems
 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
Size and design of nature preserves
 For some species with small territories, several small isolated refuges can
support viable populations
 But cannot support species requiring large amounts of space or edge
sensitive species
 Corridors of natural habitat to allow movement of species from one area
to another can help maintain genetic exchange in fragmented areas
Corridors
 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
Conservation of ecosystems