Studies Of Island Biogeography Research Articles

Integrating traditional knowledge, science and conservation in the search for undescribed mammals on Malaita, Solomon Islands

Basic knowledge of species diversity and distributions underpins the study of island biogeography and is fundamental for conservation planning. In Solomon Islands, new mammals continue to be described and several lineages are yet to be documented from large islands where, presumably, they should occur. On Malaita and Makira, no giant rats (Solomys or Uromys), or monkey-faced bats (Pteralopex) have been documented by scientists, but traditional knowledge suggests they exist. In East Kwaio, Malaita, we combined traditional knowledge and scientific methods to survey mammals and search for these taxa. Camera traps, mist nets, spotlight surveys, echolocation call recorders, rat traps and active searches were used to produce an inventory of the island’s mammals. No Solomys, Uromys or Pteralopex were captured. However, detailed accounts suggest that giant rats and monkey-faced bats were present as recently as 1996 and 2002 respectively. Moreover, we consider the presence of gnawed Canarium nuts an indicator that giant rats still persist. The human population of Malaita is dense, hunting pressure appears high, feral cats are common, and logging is rapidly reducing primary forests. A notable feature of this work has been the commitment towards collaboration and upskilling landowners in mammal survey techniques. This collaboration has helped fuel a growing conservation movement on Malaita and led to the designation of three large conservation areas. Gathering evidence for the existence of undescribed mammals on Malaita is paramount for reducing further extinctions in Melanesia. Continued support for skilled community members in East Kwaio will be key to collecting this evidence.

Divergence in New Holland Honeyeaters (Phylidonyris novaehollandiae): evidence from morphology and feeding behavior

Studies of island versus mainland populations have provided insights into processes that shape adaptive divergence (e.g., through selection in allopatric populations) as well as patterns of morphological change. In this study, we compare the morphology and foraging behavior in New Holland Honeyeaters (Phylidonyris novaehollandiae) between Kangaroo Island and the South Australian mainland. We (1) provide descriptive information on morphology traits across populations to test previously described differences; (2) test the prediction that island birds will have a wider foraging niche, different use of foraging substrate, and different foraging techniques, and (3) test for evidence of reduced prey diversity on islands as evidenced by longer foraging time. The results provide support for the predictions. Island birds were larger than the mainland birds in tarsus (2.5%) and bill length (3.7%), had a wider foraging niche (mostly due to greater insect consumption), and foraged more from the bark and air (sallying). Consistent with other studies of island biogeography, at least one common mainland predator and several bird species are absent from Kangaroo Island, which may facilitate niche expansion in the island birds. A wider niche could also be favored by lower prey diversity on islands (a depauperate community): in this study, island birds had longer foraging times than mainland birds, which may be evidence for lower total prey density.

Presence, richness and extinction of birds of prey in the Mediterranean and Macaronesian islands

AbstractAim We analyse modern patterns of richness, presence and extinction of birds of prey (Accipitriforms and Falconiforms) in the Mediterranean and Macaronesian islands, using an integrated approach involving both biogeographical and human‐induced factors.Location Forty‐three islands grouped into nine Mediterranean and Macaronesian archipelagos.Methods Information about 25 species breeding during the past century and their fate (permanence or extinction) was compiled from the literature and regional reports. Jaccard's similarity index and cluster analyses were applied to define island assemblages. In order to detect the factors driving richness, presence and extinction, generalized linear models (GLM) were applied to 32 explanatory variables, evaluating location, physiography, isolation of island, taxonomic affinities and life‐history patterns of the raptor species.Results Islands belonging to the same archipelago clustered when raptor assemblages were compared, revealing a marked biogeographical signal. Species richness was influenced by island area and accessibility from the continent (explained deviance of 51% in the GLM). Models of the probability of presence (explained deviance of 32%) revealed positive influences of migratory patterns (maximum for partial migrants), size of distribution areas and proximity to main migration routes. The model for probability of extinction explained only 8% of the deviance. It revealed that populations living on islands with a high density of human population were more prone to disappear. Also, raptors depending on human resources had more risk of extinction.Main conclusions Basic predictions of island biogeography can explain current patterns of raptor richness in the study area despite millennia of intense humanization processes. Colonization success appears to depend on life‐history traits linked to migratory and dispersal strategies, whereas body‐size constraints are not influential. Additionally, our results reveal the importance of species‐based analyses in studies of island biogeography.

Evidence for rapid faunal changes on islands in a man-made lake : I. Ants.

Few studies of island biogeography have been made on islands in which the time of insularization is precisely known. We tested the effects of island formation on ant species diversity in a man-made lake in South Africa, to determine whether island effects are detectable after only 16 years of insularization. The number of ant species observed at trap-line censuses on islands was significantly correlated with island size (r=0.608; P<0.05) and ant species diversity was generally low compared with similar mainland habitats. Mean species number for all islands, including landbridge islands, was 5.5±3.3 species, and on mainland sites was 7.9±2.85 species. Island effects were more marked on islands <20 ha, which had a mean of 3.3±2.5 species per island. Species number on islands was inversely related to densities of the aggressive Anoplolepis custodiens and A. steingroeveri. These two species were only patchily distributed on mainlands, but these ants were nearly ubiquitous on small islands. Several lines of evidence suggest that this single species domination may be responsible for island effects. Island sites also differed in the number of ant species in different trophic groupings, tending to have fewer granivorous species than the mainland sites, but species in other diet groups were similar in both island and mainland habitats. We conclude that there have been marked changes in the ant faunas on islands smaller than 20 ha apparently due to changes in abundance of the dominant ant species. However, the causes of these changes are unknown.

Species Movement in Zoogeography

Theories of the relationships involved in species movement between different zoogeographic regions or subregions are examined, and the conclusion reached that it is not necessary to invoke the concept of relative species dominance as a determinant of the direction of species movement in many cases. Alternative views are put forward, using techniques similar to those developed by Macarthur & Wilson in their study of island biogeography. The theory of the relationships between different zoogeographic regions or subregions has not been examined in detail, although I have elsewhere (Horton, 1973a, b, 1974) looked at some aspects of the problem. Darlington (1957) examined these relationships qualitatively and suggested that the main factor determining direction of species movement between -such regions was the relative dominance of the groups in the areas concerned. Simpson (1950) documented the interchange of species between the nearctic and neotropical regions and also reached the conclusion that dominance determined the direction of species movement. I have suggested (Horton, 1974) that it is not necessary to use the concept of dominance to explain Darlington's and Simpson's findings, but that the patterns of climatic change in different regions provide a sufficient explanation. It should, nevertheless, be possible to make some generalizations about patterns of dispersal and this study is an attempt to find such generalizations. Macarthur & Wilson (1963, 1967) expressed the hope that the methods they developed for the study of island biogeography could be extended to encompass other aspects of zoogeography. This study uses similar techniques modified to allow for an interchange of species between two regions, rather than the one way flow of species from the mainland to an island. Let us consider two areas, A and B, separated by a barrier. Let each contain ten species and let each satisfy the following conditions: (1) no previous contact between A and B; (2) both A and B have reached equilibrium with other areas, i.e. they are holding an equilibrium number of species with extinction balancing immigration; (3) all species in A and B are equally likely to