(1) Biodiversity in the Anthropocene Flashcards
What is the normal background rate of extinction?
0.25 extinction per million species years
Give 2 reasons for why actual rates of extinction are much higher.
(1) Hunting by humans - Post-Pleistocene losses were smallest in Africa (followed by Asia and Europe) reflected that humans have been present here for a longer period. Higher rates of losses were observed in the early/mid-Pleistocene. These extinctions can be linked to humans because the lost species had survived previous interglacial period so unlikely to be due to climate change. Further evidence that humans lead to extinctions – subfossils suggest Polynesians eliminated 1000 to 2000 endemic birds.
(2) Environmental conditions are declining - Ripple et al., (2017) showed freshwater is declining, marine catches are increasing, dead zones are increasing, total forest are declining, vertebrate species are declining, CO2 emissions are increasing, temperatures are increasing, human and ruminant livestock populations are increasing.
What did Barnosky estimate the time to 75% species loss was?
240 to 540 years.
Barnosky et al. (2011) estimated that if all threatened species became extinct in 100 years and the rate of extinction remained constant, the time to 75% species loss would be 240 to 540 years. (75% represents a mass extinction event).
EXTRA READING for Anthropocene extinction predictions?
Ceballos et al. (2015) showed that the rate of vertebrate extinction is currently higher than the last five mass extinction events and is 100 time greater than the background rate. This study used a conservative estimate a 2 mammal extinctions per 10,000 species per 100 years (2 E/MSY) as the background rate. If the extinction of the last century had occurred at the normal background rate they would have taken 800 to 10,000 years to all go extinct.
Ceballos et al, (2017) showed that even “species of low concern” are being affected by the Anthropocene. They showed a high degree a population decay in vertebrates through reduced population sizes and range shrinkages. Of the mammals studied all had lost 30%+ of their geological range and 40% had experienced server population declines.
What are some problems with extinction predictions?
- Predictions may be extreme.
- Most species have already gone extinction so remaining species may be more resilient.
- Population monitoring may not account for species altering distributions and new populations.
- Conservation may avert species extinctions
- Most unknown species have small ranges and are likley to be threatened so estimates are probably too low.
Name 2 studies about conservation efforts in regards to problems with extinction predictions.
PLUS EXTRA READING
Pimms et al (2006) suggested that the extinction rate in the last decade was <50 E/MSY but would be 150 E/MSY if it was not for conservation efforts.
Taylor et al (2005) examined population trends for species listed as threatened or endangered and found that species with protected habitat were more than twice as likely to be increasing and less than half as likely to be decrease, compared to those without. Species with a dedicated recovery plan were also more likely to be increasing and less likely to be decreasing.
EXTRA READING - Hoffmann et al (2015) showed through a scenario-based thought experiment in which conservation efforts of 235 ungulate species stopped in 1996, that without conservation efforts 148 of the ungulate species would have decline a IUCN Red List category compared to where they actually were in 2008. 8 of these species would have also gone extinct in the wild. Overall, the decline would have been 8 times worse than if there were no conservation efforts. This shows that conservation efforts can prevent extinctions.
Two addition factors that may mean extinction estimates are too low are disease and climate change. Give examples.
Disease - e.g. Batrachochytrum dendrobatdis causing amphibian extinctions
Climate change - e.g. rapid climate change (second wave of island extinctions). Hawaiian honeycreepers. In 1827 Culex pipiens (mosquito spp.) was introduced onto Maui by British sailors from a whaler cleaning out water barrels. Followed by an epidemic of avian malaria and pox. All lowland endemic now extinct but some species still present in the uplands. Malarial parasite has minimum temperature requirement to complete development with vector. Warming climate may be extending upper elevation of both mosquitoes and malarial parasite into uplands.
The Anthropocene also means there is higher connectivity between land masses. This creates mixing of species leading the evolution of new species. What are the 3 mechanisms of enhances Anthropocene evolution?
Geographical separation
Opportunism
Hybridisation
What is geographical separation as a mechanism of enhanced Anthropocene evolution? Example?
Colonists will evolve separately from their parent population and eventually form separate species e.g. star thistles introduced from Europe to North America in past 100-200 years already reduced fertility when crosses with European plants.
What is opportunism as a mechanism of enhanced Anthropocene evolution? Example?
Residents will take advantage of newly-arrived novel host plants and eventually diverge into ecologically separated populations e.g. caterpillars of one third of all 236 native butterfly species in California included newly-arrived exotic plants in their diet. Even though these plants have been growing in California for less than 200 years. In some cases, individuals feeding on new species of host plant can have different development rates, adult emergence times etc., reduced gene flow with those feeding on native plants.
What is hybridisation as a mechanism of enhanced Anthropocene evolution? Example?
Colonists will hybridise with resident species to produce offspring incompatible with either parents. Hybrid generation of new plant species could even outstrip the rate of extinction. E.g. Yorkwort (Scenecio eboracensis). A new species derived by hybridisation between Oxford ragwort and groundsel at the end of 1970s.
