The numbers of land birds, waders, sea birds, land crustacea, and certain insects on the lagoon islands of Aldabra Atoll

Abstract

A \rudy was niatle of the deterniinants of numbers of' species of land birds, waders, hrcrdirig sea l>it.cl\. land crustacea, and insec-ts on 7 7 ofthe lagoon islands of Aldabra Atoll in the Western Indian Owan. By comparison with other studies, number of plant species and the structural conqdexity of tlic vcgcration arc riot significantly related to the number of land bird species; log area accounts for 66.5% ol.thch variance in riutnber. Log area is also the most important fictor influencing the nunthc-r ol'watle~-spcciec. The variables considered account for only 36.2% of the variance in breeding sea t ) i i d spcacies; this low ligitrr suggests that other factors are of iniportance. Isolation ofan island is the mo\t iniportant o l those coilsidered. Nearly hall the variance in the numbel. of insects groups is clctc~rniined by log number of plant species. while the complexity of the vegetation structure is the oiily rigiiilic;rnL variable predicting the number of speries of land crustarea. Differences berwwn the liliclinp o f this and other studies are attributed t o the particular characterisrics or the islands a n d \pc.cies considrrctt.Kclaiivrlv low z values are lound (0.205 for land birds, 0.174 for Nsaders, and 0.136 for land ( I ti&rccd, ruggesting that inter-island distances do not rcpresc.ttt great I J~I I k t \ to tk 51)c.c k + ~~oncc~riic~ct and itiiinigration and extinction rates are probably in cquililxiuni.

Shipwrecked on the Rock, or Not Quite: Gypsophytes and Edaphic Islands

“…The concept of SAC antecedes that of ISAR (island species-area relationships) [3]. SAC have been employed for a considerable period of time to delineate how the number of species increases with the size of the sampled area [4][5][6][7] or the area of various islands in an archipelago [8][9][10]. According to Gleason [11], this concept was initially formalized by Arrhenius [12] in a mathematical model with the expression S = c•A z , where S represents the number of species, A is the area, c is a coefficient, and z is the slope of the model.…”