Flashcards in Extinction and Biodiversity Loss Deck (52):
How many Earths were needed to sustain the human population in 2020
If current trends continue, what will be the impact on vertebrates?
There will be a 67% loss of populations in 2020 compared to 1970
How many species are there?
Estimates provided by ecologists range from 3-100 million, however the most plausible range is 3-30 milllion
What is the number of living species currently known and how are they distributed?
Roughly 1.6M, arthropods account for >50% of all monographed species diversity
Discuss the idea that 5% of the worlds species are found in the UK
hugely overestimated because the British biota is much better known against the world average and only a small proportion of these species are endemic to the UK
What are the scales of extinction processes
1. Global extinction
2. Extinction in the wild
3. Regional extinction
4. Local extinction
5. Ecological extinction
6. Economic extinction
What percent of the worlds species have gone extinct? cite
99.9% have gone extinct (Raup,1991)
Post-human drivers of extinction?
Describe the Island equilibrium theory
As the number of species on a island increase, the rate of immigration decreases and the rate of extinctions increase until the two line cross and settle at an equilibrium
What effects the immigration and extinction rates of an island
The island's distance from the mainland and it's size
Describe how an island's distance from the mainland can effect the island equilibrium
Immigration rates will be higher on closer islands due to the ease of access
Describe how an island's size can effect the island equilibrium
Large islands have more resources so the rate of extinction is low
How many recorded extinction have there been in the last 400 years, and how have they been distributed?
There have been 724 recorded animal extinctions in the last 400 years, about half were of island species. At least 90% of the bird species that have become extinct in that period were island-dwellers.
What makes island species so vulnerable to extinction?
Why are contemporary extinctions not as high as predicted
Conservation efforts, surviving in managed landscapes such as agricultural and secondary forest and extinction debt
What is extinction debt
The idea that apecies can initially survive habitat change but will later become extinct without any further habitat modification e.g a long living tree who's seeds can no longer root, but the tree remains alive for a long time
How are most extinction rates inferred?
Through species-area relationship equatons
What is the discrepancy between predictions made by species-area relationship equations and recorded extinction rates
more species are left after a given loss of habitat than the number of species predicted to remain, based on SARS
What is EAR
Why is there a discrepancy between predictions made by species-area relationship equations and recorded extinction rates
The area required to remove the last individual of a species (extinction) is larger, than the sample area needed to encounter the first individual of a species, irrespective of species distribution and spatial scale.
Give an example of when SARS has been inaccurate
The pre-Colombian extent of the Atlantic forest (~1 mill km2) had been reduced to ~8% of its original forest cover by 1990. Currently only 4 species are considered to be virtually extinct, but three of these have been “rediscovered” recently. The predicted number of extinctions was roughly 341
What are the estimations for co-extinction and who found them
Using nomographic method based on mean host specificity (number of host species per affiliate species), there are and estimated 6300 affiliate species which are “coendangered” with host species currently listed as endangered. (Koh et al. 2004)
What is the old background extinction rate and who gave the estimate
Raup (1978) based on a large number of cohorts of marine invertebrate fossil genera estimated that 9% of all species went extinct every 10^6 yrs ≈ 0.2 species/yr
What are the current extinction rates and who gave the estimate
Current rate: Wilson (1989, 1992) based on a
perhaps conservative tropical deforestation rate of 0.7%– 1.8 yr–1 estimated 17,500 – 27,000 species extinct/yr
Why is it difficult to declare an organism extinct
Probability of detection: small populations may persist
undetected in remote areas
A time lag of up to 50 yrs without “rediscovery” records is often required before a species can be declared terminally extinct (e.g. Ivory-billed woodpeckers; Reported sightings but no conclusive evidence for an extant population.
Difficult to name species that have become extinct recently because it is hard to say with conviction that a species is extinct (e.g. Bermuda petrel thought to be extinct for almost 3 centuries but rediscovered)
Interference from ex-situ conservation measures
Very few arthropod species recorded as extinct; biases in the records for more charismatic organisms
What are the issues with species-area predictions
Does not consider patterns of habitat fragmentation;
Does not consider the effects of habitat insularization on different groups of organisms across a range of habitat tolerance to the intervening matrix;
Many habitat types surrounding remnants of primary
habitat are semi-permeable to dispersal;
Does not consider differential uses of secondary habitats e.g. second-growth matrix around forest isolates in continental areas;
Who is the main criticizer of SARS
He and Hubbelll 2011
What is habitat loss?
The destruction of a habitat inhabited by an organism
What is fragmentation?
process whereby a large continuous area of habitat is both reduced in area and divided into smaller fragments where original populations are divided into smaller subpopulations; produces a series of remnant vegetation patches surrounded by a matrix of different vegetation and/or land use.
What are the effects of fragmentation?
• Initial exclusion
• Barriers and isolation
• Crowding effect
• Reduction in total and effective
• Stochastic loss (genetic drift)
• Loss to inbreeding depression
• Truncation of the habitat matrix
• Intrusion of edges (Edge Effects)
• Biological invasions
Why does fragmentation cause loss to inbreeding depression?
A genetic bottleneck occurs, decreasing the genetic variability of the isolate population, which increases the chances of offspring inheriting deleterious recessive genes normally suppressed by heterozygosity
Define edge effect?
The result of the interaction between two adjacent ecosystems separated by an abrupt transition
Describe the process of edge effect
As patches become smaller their ratio of edge to interior increases disproportionately
Small habitats have less or no
interior (or core) habitat
In small fragments, ecosystem
dynamics are probably driven
predominantly by external rather
than internal forces
What are some abioitc edge effects, who described them?
The climate in crops and pastures tends to be dryer and temperature fluctuates more steeply due to more sun being able to hit the ground an reradiate. In forests the climate is cooler, moister and more uniform. A gradient is formed between these two microclimates which can effect the biomass (Murcia 1995)
Negative effect of edge effect
(b) More fragmented landscapes contain more
edge for a given amount of habitat;
(c) Negative edge effects due to adverse species
(d) Negative edge effects due to unfavourable
Example of increased predation due to edge effect, and cite
Experimental quail nests were positioned at various distances away from the forest edge. There was a negative e correlation between distance from the forest edge and the percentage of predation (Wilcove, 195)
When is edge effect a good thing
They support ecotonal species such as Lantana canescens, a rare tropical shrub native to the ecotone between pine and hardwood forests of Miami-Dade County, Florida, U.S.A. (Possley et al. 2008)
Many species require more than one type of habitat
If habitat amount is held constant, increasing fragmentation per se actually implies smaller distances between patches.
What is a mesopredator
middle predators who's numbers are often limited by apex predators
What is a keystone species
species (and some would argue processes) that have
a disproportionate effect on the persistence of all other species. (e.g. extinction, large changes in density); exert strong control on community structure not by large numbers but by their ecological roles, or niches.
How does fragmentation effect mesopredators
Small fragments can not support large predators. Consequently mesopredators numbers will increase which will have a negative effect on their prey population
What benefits do keystone predators bring to an ecosystem
Feed on competitive dominants
Can enhance local species diversity
Prevent competitive exclusion among prey
Explain sea-otters keystone role in maintaining biodiversity on the Pacific coast of North America
Sea otters feed on sea urchin. When the otters declined in the 20th century through fur
trapping and removal by fishermen, sea urchin
populations skyrocketed and grazed heavily on
macroscopic algae and kelp. Some kelp forests were destroyed which in turn lowered the diversity of other plants and animals in that habitat. Reintroduction of sea otters reversed this situation, and kelp beds recovered.
What category of keystone species are there
What are the effects removing a keystone predator
Increase in one or several predators/ consumers/
competitors, which subsequently extirpates several
prey/competitor species (sea otters)
What are the effects removing a keystone prey
Other species more sensitive to predation may
become extinct; predator populations may crash
What are the effects removing a keystone plant
Extirpation of dependent animals, potentially including
pollinators and seed dispersers
What are the effects removing a keystone link
Failure of reproduction and recruitment in certain
plants, with potential subsequent losses
What are the effects removing a keystone modifier
Loss of structures/materials that affect habitat type and
energy flow; disappearance of species dependent on
particular successional habitats and resources
How many species are threatened by invasive species
42% threatened or endangered species are primarily at risk from invasive species
Where is the small Asian mongoose from?
South and Southest Asia
How did it become an invasive species
Introduced to the Pacific Islands and Caribbean to control rats, but became a failed biological control