Habitat diversity predicts orchid diversity in the tropical south-west Pacific

• Published in: Journal of biogeography Vol. 43; no. 12; pp. 2332 - 2342
• Main Authors: Keppel, Gunnar, Gillespie, Thomas W., Ormerod, Paul, Fricker, Geoffrey A.
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing Ltd 01.12.2016; John Wiley & Sons Ltd; Wiley Subscription Services, Inc
• Subjects: Age; Biodiversity; climate; Climate variability; Correlates of diversity and turnover; Correlation; Curvature; Endemic species; endemism; Environmental factors; environmental heterogeneity; habitat diversity; Habitats; Heterogeneity; Indicators; island biogeography; Islands; Orchidaceae; Species diversity; Species richness; Species-area relationship; Temperature effects; Topography; Variability; Variables
• ISSN: 0305-0270; 1365-2699
• DOI: 10.1111/jbi.12805

Aim: To determine if habitat diversity, as estimated by climatic and topographic variables, can predict patterns of orchid diversity on different islands and archipelagos with similar explanatory power to biogeographical variables, such as area, isolation and age of an island. Location: Sixty-three islands on eight archipelagos (Solomon Islands, Vanuatu, New Caledonia, Fiji, Samoa, Tonga, Niue and the Cook Islands) in the southwest Pacific. Methods: For each island, we determined the orchid species present, age, area, isolation, and indicators of topographic heterogeneity and climatic variability. We then determined the power of various biogeographical, climatic and topographic variables to predict the number of indigenous and endemic species on archipelagos, and on islands within archipelagos, using generalized linear models (GLMs) and generalized linear mixed models (GLMMs) respectively. Results: We identified a total of 552 species in 110 genera. Area was the only significant biogeographical variable for predicting patterns of orchid species diversity on archipelagos and islands. However, climatic and topographic predictors of habitat diversity performed similarly well. The range in curvature was the best indicator of species richness from the topographic variables, while the range of temperature was the best climatic predictor. These key variables were often strongly correlated with area. Main conclusions: Climatic and topographic variables are useful indicators of habitat diversity. The high explanatory power of area and climatic and topographic predictors, and the strong correlation among these variables, suggests that increasing habitat diversity with increasing area may be the major driver of the species—area relationship. Using climatic and topographic variables as predictors of species richness therefore allows determining the key environmental factors and processes driving species diversity.