The above figure shows the trajectory of arthropod species richness over time fo

Question

The above figure shows the trajectory of arthropod species richness over time for four mangrove islands after fumigation to remove all arthropods. The single values on the left show the total no. of arthropod species on each island before fumigation. The islands are labelled, in order of distance from the mainland, as E2, E3, ST2 and E1. The islands were of roughly similar size.

Question 1. What prediction(s) of the theory of island biogeography do these data support?

Question 2. What do you predict the species richness of each island will be 1000 days after fumigation? Why?

Explanation / Answer

"Island" is the area of habitat suitable for a specific ecosystem, surrounded by an expanse of unsuitable habitat. mass of land surrounded by water—the term may also be applied to many nontraditional "islands", The peaks of mountains, isolated springs or lakes surrounded by desert,& non-contiguous woodlands.The concept is applied to natural habitats surrounded by human-altered landscapes, some organisms located on mountaintops may also be found in the valleys, while others may be restricted to the peaks

The theory of insular biogeography proposes that the number of species found in an undisturbed insular is determined by immigration& extinction. Immigration & emigration are affected by the distance of an island from a source of colonists . Usually this source is the mainland, . Islands that are more isolated & are likely to receive immigrants than islands that are less isolated.

The rate of extinction once a species manages to colonize an island is affected by island size; this is the species-area curve Larger islands contain larger habitat areas & opportunities for more different varieties of habitat. Larger habitat size reduces the probability of extinction due to chance events. Habitat heterogeneity increases the number of species that will be successful after immigration.Over time, forces of extinction& immigration result in an equilibrium level of species richness.

The theory can be studied through the fossils, which provide a record of life on Earth. 300 million years ago As, Europe &North America lay on the equator & were covered by steamy tropical rainforests. Climate change devastated these tropical rainforests during the Carboniferous Period &as the climate grew drier, rainforests fragmented. Shrunken Island
of forest were uninhabitable for amphibians but also well suited to reptiles, which became more diverse & even varied their diet in the rapidly changing environment; this Carboniferous rainforest collapse event triggered an evolutionary burst among reptiles.

Influencing factors:

Degree of isolation ie distance to nearest neighbour, and mainland

Length of isolation (time)

Size of island The larger area usually facilitates greater diversity

Research conducted at the rainforest research station on Barro Colorado Island has yielded a large number of publications concerning the ecological changes following the formation of islands, such as the local extinction of large predators and the subsequent changes in prey populations.

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