Tropical ecosystems

Question 1

Who was Alfred Russel Wallace?

Answer 1

an early explorer of the indo-west pacific, theorized evolution by natural selection (focussed on insect & plants), worked for his money

Question 2

Who was Alexander Von Humboldt?

Answer 2

the first person to formally recognise the latitudinal diversity gradient, i.e. that there is a higher species diversity in the tropics

Question 3

What are the 3 hypotheses as to why biodiversity is highest in the tropics?

Answer 3

ecological (larger area) evolutionary (speciation/extinction rates), and historical (tropics are older) hypotheses

Question 4

What is meant by the tropics being a “cradle” of biodiversity?

Answer 4

area of radiation / development of new species

Question 5

What is meant by the tropics being a “museum” of biodiversity?

Answer 5

area where species originate and inhabit until extinction

Question 6

What are the 3 definitions of the tropics?

Answer 6

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

Question 7

What 2 factors contribute towards the biogeographic edges of the tropics?

Answer 7

clusters of species geographic range limits and steep gradients in species richness

Question 8

Why do islands appear further apart in the tropics?

Answer 8

higher water temperature in the tropics increases metabolic rate, reduces life span, speeding up growth rates for larvae, allowing for shorter dispersal distances

Question 9

How do tropical conditions facilitate allopatric speciation?

Answer 9

warm temperatures limit dispersal/gene flow, making islands harder to colonise

Question 10

Why are clams, snails / bivalves and gastropods used as a marker for biodiversity in the tropics?

Answer 10

They are the most diverse marine invertebrates, have an extensive fossil record, well known taxonomy, and a well studied ecology.

Question 11

what rates need to be tested to study tropical geographical distribution?

Answer 11

origination, extinction, and dispersal rates

Question 12

Define a reef

Answer 12

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”

Question 13

What are the 2 main types of reef

Answer 13

biogenic reefs (created by animals) and abiotic reefs

Question 14

Describe Cloudina reefs

Answer 14

the earliest known reef / shell-builders, 8-150cm in length

Question 15

Describe Archie reefs

Answer 15

Palaeozoic reefs, probably porifera/sponges, home to a high diversity of marine invertebrates

Question 16

Describe Palaeozoic coral reefs

Answer 16

Rugosa (“horn corals”) and Tabulata, both of which went extinct at the end of the permian period

Question 17

Describe Rudist Bivalve reefs

Answer 17

mesozoic reefs, highly diverse during the cretaceous period, out-competed corals, 100s of metres tall

Question 18

Describe scleractinians

Answer 18

early scleractinians did not build reefs, but reef diversity peaked during Jurassic period. 18 genera are alive today.

Question 19

What 2 types of corals are in Scleractnia?

Answer 19

hermatypic and ahermatypic corals

Question 20

What is the difference between hermatypic and ahermatypic corals?

Answer 20

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

Question 21

Describe the cradle scenario in terms of speciation and extinction rates with latitude

Answer 21

cradle = high speciation, equal extinction around the tropics

Question 22

Describe the museum scenario

Answer 22

museum = low extinction, equal speciation

Question 23

Describe the “out of the tropics” scenario

Answer 23

low extinction rates and high speciation rates - species disperse out of the tropics over time

Question 24

Describe the “into the tropical museum” scenario

Answer 24

low extinction rates and equal speciation rates - species move into the tropics over time

Question 25

Why are temperate gastropods along the eastern pacific coast more able to move into the tropics than tropical species moving out?

Answer 25

there is less distance between habitats/”islands” in temperate areas, and cooler temperatures along for longer dispersal distances. This combined with an adaptation for seasonal conditions means eastern pacific gastropods can easily disperse into tropical regions.

Question 26

Which distribution scenario is demonstrated by eastern pacific gastropods?

Answer 26

the “into the tropical museum” model - low extinction rates and equal speciation rates causing gastropod species to disperse inwards

Question 27

Which distribution scenario is demonstrated by eastern pacific bivalves?

Answer 27

the “out of the tropics” model - high speciation rates and low extinction rates causing bivalve species to disperse outwards