exam II: supplement 7 & 8 Flashcards
types of extinction
- extinct: a species is considered extinct when no member of the species is found alive anywhere in the world
- extinct in the wild: when individuals of a species remain alive only in captivity or in other human-controlled situations
- globally extinct: the ubiquitous disappearance of a species (encompasses extinct and extinct in the wild)
- locally extinct: when a species is no long found in a specific area it once inhabited but is still found elsewhere in the wild
- regionally extinct: when a species is extinct in a country or region but still persists in another part of its range
- ecologically extinct: if a species persists at such reduced numbers that its effect on the other species in its community are negligible
blitzkrieg hypothesis
describes a process whereby megafauna that have not previously encountered humans, are rapidly and selectively hunted to extinction immediately following first contact
- originally called the “overkill hypothesis”, served to describe the extinction of North American Pleistocene megafauna
- model: when people colonize new lands, megafauna (and often other animals) go extinct
evidence against alternative blitzkrieg hypothesis
- rates of megafauna extinction have been much higher on landmasses only colonized by hunter-gathers in the last 60,000 years or so
- remote island species, not previously exposed to humans are pathetically vulnerable to to human predation
- ethnographic data and theoretical modeling suggests that hunter-gathers preferentially select larger prey
- climate change can be eliminated to the short-list of alternative causes due to the climate fluctuation during late quaternary resulting in no wide spread mass extinction
evidence for alternatives to blitzkrieg
- climate, glaciers, specific period of climate change during glacial retreat and non-heightened sea levels
- –very specific time period to cross land bridge
- other factors, humans might have contributed because hunting is quite likely, but other factors played a larger role
- –mass killing sites only found in North America
- –australia does not have mass killing sites but megafauna still gone in this region
notion FOR sixth extinction being caused by human activity
- present geological period has more species than any other, yet the current rate of extinction is greater now than at any time in the past million years
- ecosystems and communities are being degraded and destroyed and species are being driven to extinction—causing loss in biodiversity at all levels is in the range of human activity that alters and destroys natural habitats to suit human needs
- approximately 80% of megafauna are extinct
- –caused directly by hunting and indirectly by the burning and clearing of forests and grasslands, and intro. of invasive species and diseases
notion AGAINST sixth extinction being caused by human activity
- extinction rates for the other 99% of the world’s species (non land vertebrates such as birds and mammals) are roughly estimated due to the limited of taxonomy
- there has been an apparent decline in extinction rates since 1950 due in part to deliberate efforts to protect rare species in danger of going extinct, as well as to the current practice of not declaring a species extinct until decades after it has no longer been found
- no documented cases of marine fish or coral species that have gone extinct during the last few thousand years
- important*
- scientists do not know how many species we have on earth, so we do not know an accurate rate of extinction
- ecological time v. physiological time
island biogeography model
describes relationship between the rates of colonization and extinction on islands
-number of species occurring on an island represents a dynamic equilibrium between the colonization and evolution of new species and the extinction rate of existing species
species-area relationship
islands with large areas have more species than islands with smaller areas
- 50% of island destroyed=10% of species eliminated
- –endemic species will become extinct regardless
- 90% of island destroyed=50% of the species eliminated
- 99% of island destroyed=75% of species will be lost
factors that make species vulnerable to extinction
- species with a narrow geographical range
- species with only one or a few populations
- species in which population size is small
- species in which population size is declining
- species that are hunted or harvested by people
categories that have also been linked to extinction
-species that need a large home range
-animals species with large bodies
-species that are not effective dispersers
-seasonal migrants
species with little genetic variability
-species with specialized niche requirements
-species that are characteristically found in stable, pristine environments
-species that form permanent or temporary aggregations
-species that have not had human contact
-species that have closely related species that recently extinct or are threatened with extinction
endangered species act (ESA)
provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved to provide a program for the conservation of such species
ESA value
species that are threatened or endangered are placed on the official list for protection
ESA problems
- most are flowering plants and vertebrates, despite the fact that most of the world’s species are insects and other invertebrates
- only about 1000 individuals remain at the time a given animal is listen
- species dependent not habitat dependent, which sucks
ESA solutions
- greater efforts need to be made to study lesser known and underappreciated invertebrate groups and extend listing to those endangered species whenever necessary
- endangered species must be given protection before they decline to a point where recovery becomes virtually impossible
- early listing of a declining species might allow it to recover and thus become a candidate for removal from the list more quickly than if authorities were to wait for its status to worsen before adding it to the list
- use indicator species to measure the health of the habitat
