Tropical ecosystems Flashcards
Who was Alfred Russel Wallace?
an early explorer of the indo-west pacific, theorized evolution by natural selection (focussed on insect & plants), worked for his money
Who was Alexander Von Humboldt?
the first person to formally recognise the latitudinal diversity gradient, i.e. that there is a higher species diversity in the tropics
What are the 3 hypotheses as to why biodiversity is highest in the tropics?
ecological (larger area) evolutionary (speciation/extinction rates), and historical (tropics are older) hypotheses
What is meant by the tropics being a “cradle” of biodiversity?
area of radiation / development of new species
What is meant by the tropics being a “museum” of biodiversity?
area where species originate and inhabit until extinction
What are the 3 definitions of the tropics?
Geographical/astronomical definition - region between tropic of cancer (north) and tropic of capricorn (south) in which the sun can be seen directly overhead during summer/winter solstices. Cilmatological definitions: based on temperature, precipitation patterns, etc.
Biogeographic definition: edges of tropics defined by the geographic ranges of low-latitude species coming into contact with high-latitude species
What 2 factors contribute towards the biogeographic edges of the tropics?
clusters of species geographic range limits and steep gradients in species richness
Why do islands appear further apart in the tropics?
higher water temperature in the tropics increases metabolic rate, reduces life span, speeding up growth rates for larvae, allowing for shorter dispersal distances
How do tropical conditions facilitate allopatric speciation?
warm temperatures limit dispersal/gene flow, making islands harder to colonise
Why are clams, snails / bivalves and gastropods used as a marker for biodiversity in the tropics?
They are the most diverse marine invertebrates, have an extensive fossil record, well known taxonomy, and a well studied ecology.
what rates need to be tested to study tropical geographical distribution?
origination, extinction, and dispersal rates
Define a reef
a rocky marine habitat or biological concretions that rise from the sea bed. They are generally subtidal but may extend as an unbroken transition to the intertidal zone”
What are the 2 main types of reef
biogenic reefs (created by animals) and abiotic reefs
Describe Cloudina reefs
the earliest known reef / shell-builders, 8-150cm in length
Describe Archie reefs
Palaeozoic reefs, probably porifera/sponges, home to a high diversity of marine invertebrates
Describe Palaeozoic coral reefs
Rugosa (“horn corals”) and Tabulata, both of which went extinct at the end of the permian period
Describe Rudist Bivalve reefs
mesozoic reefs, highly diverse during the cretaceous period, out-competed corals, 100s of metres tall
Describe scleractinians
early scleractinians did not build reefs, but reef diversity peaked during Jurassic period. 18 genera are alive today.
What 2 types of corals are in Scleractnia?
hermatypic and ahermatypic corals
What is the difference between hermatypic and ahermatypic corals?
Hermatypic corals a reef-building, contain zooxanthellae and photosynthesis in the photic zones of tropical latititudes, wheres ahermatypic coral and non-reef building coral without zooxanthellae found in deep and/or cold waters
Describe the cradle scenario in terms of speciation and extinction rates with latitude
cradle = high speciation, equal extinction around the tropics
Describe the museum scenario
museum = low extinction, equal speciation
Describe the “out of the tropics” scenario
low extinction rates and high speciation rates - species disperse out of the tropics over time
Describe the “into the tropical museum” scenario
low extinction rates and equal speciation rates - species move into the tropics over time
