Threats & Losses I Flashcards
What is a mass extinction?
extinction of a large number of species ( across taxa) within a short period of geological time
There have been 5 mass extinctions
cretaceous ~65 MYA
- dinosaurs, many marine species,
permian ~250 MYA
- 50% of all animal families
-95%< of marine species
-many trees, amphibians, all trilobites
What is the 6th mass extinction ?
pleistocene overkill Hypotheses
- correlated with human expansion over the planet
-exterminated many large mammals + island species
how has human activity affected extinction rates in more recent times?
- best known for birds and mammals (larger + more easily spotted) (e.g. amateur bird watchers)
extinction rates in modern times- 1600-1700: extinction rate of 1 species per decade
- 1890-1950: 1 species every year
according to the IUCN Red list of threatened species, there are _____ species threatened with extinction
41,000 species. 28% of all assessed species
-amphibian 41%
-mammals 27%
- conifers 34%
-birds 13%
-sharks & rays 37%
- reef corals 33%
what is on of the most threatened ecosystem on the planet?
Freshwater systems
- faunal depletion in NA freshwater is 5x that of terrestrial fauna
WHY?
- highly populated
- heavily used for water, transit + food
freshwater extinction rates
- approx. 1/3 are threatened with extinction
- over 10,000 fish species live in freshwater, 1/4 of vertebrate diversity
BUT ecosystem covers only a small portion of Earth’s surface
Marine extinction rates
few documented cases
- large predatory fish species and whale species have declined by 90% or more
the highest extinction rate occurs on _______
ISLANDS!!
- half of all known extinctions since 1600 were island species
e.g. extinctions of birds on pacific islands in the wake of Polynesian colonization
- over 2,000 species (mostly flightless rails) are exticnt
why are island species so susceptible to extinctions?
-highly specialized, unaccustomed to invasive species (e.g. mongoose, rats)
-small populations are more prone to chance extinction, smaller gene pool
-introduction of disease
- smaller chance of rescue effect
drivers of biodiversity change ( threats)
increasing human population
great acceleration
- increased energy + water use
the ecological footprint is a measure of what?
how much area of biologically productive land and water an individual, population or activity requires to produce all the resources as it consumes and to absorb the waste it generates
–> how much demand human consumption places on the biosphere
what is biocapacity ?
the area of productive land available to produce resources or absorb carbon dioxide waste, given current management practices
What is the biggest pressure on biodiversity world wide?
Habitat loss and degradation
What is the biggest source of habitat loss in terrestrial ecosystems?
Conversion of wild lands to agriculture
Now accounts for 30% of land globally
Why does FAO forestry data show a decreased rate of loss?
Rate of loss slowed between 1990-2020, due to reduced deforestation, + reforestation and the natural expansion of forest
Contextualizing FAO slowed rate of loss
Many of the studied forest were cut hundreds of years ago, and may be regenerating only now
Tropical rainforest land coverage
Occupy only 7% of earth’s land,but are estimated to contain > 50% of terrestrial species
Importance of tropical moist forests
Regional importance in protection of water sheds
Global importance as Co2 sinks
Easily degraded + eroded
Land change in tropical moist forest
60% is lost from small-scale cultivation (shifting cultivation)
Degraded for firewood
~20% destroyed through commercial logging
~10% destroyed for cattle ranching
Reasons for land change in tropical deciduous forests
More suitable for agriculture & ranching than rainforest (easier to clear & burn)
Population density is 5x higher in dry forest areas
Grasslands land change
Cover 3 x area of tropical forests
Have been almost completely destroyed by Humans
Ex: only 3% of tall grass persist in NA
Wetlands land change
64% of the world’s wetlands have disappeared since 1900
Wetlands (helpers et al. 2008)
- no area is unaffected by human influence and that 41% are affected by multiple drivers
- areas of little impact are near the poles
Coral reef composition
High richness of organisms
~1/2 of the ocean’s fish species in only 0.2% of its surface area
Coral reef land change
10% of coral reefs have been destroyed
Bc: overfishing, over-harvesting, pollution, invasive species, climate change
What is coral bleaching?
Corals stressed by changes in conditions such as Temperature, light or nutrients,
they expel the symbiotic zooxanthellae living in their tissues and turn completely white
