Abstract
The peninsula effect is a biological diversity pattern found in peninsulas in which the number of species decreases toward the tip of the peninsula. The geometry hypothesis, as one proposed cause of the peninsula effect, attempts to predict this pattern by examining the peculiarities of peninsular geometry. As peninsulas are characterized by their isolated positions, it has been suggested that a decreased immigration-to-extinction rate is the cause of the decrease in species diversity from the base to the tip of a peninsula. We aimed to test the geometry hypothesis on tree species in the Florida peninsula by modeling the latitudinal abundance pattern using sample-based tree inventory data. We postulated that the current abundance distribution of a species is a ramification of past immigration–extinction dynamics in a peninsula, as well as an important indicator of such dynamics in the future. The latitudinal abundance patterns of 113 tree species in Florida in the southeastern United States were simulated with the Huisman–Olff–Fresco (HOF) model using the USDA Forest Service’s Forest Inventory and Analysis (FIA) database. Evidence species for the geometry hypothesis were then selected if the simulated latitudinal abundance pattern was asymmetric with its abundance maxima occurring within the Florida peninsula (i.e., approximately 31.5° latitude or lower). Our HOF model results found that most species (87% of 113 species) did not experience any steep abundance decline along the Florida peninsula when compared with their general trend across the range, suggesting that the observed diversity pattern of tree species in Florida could merely be a continuation of latitudinal diversity gradients in the southeastern United States, independent of peninsular geometry.
Highlights
The study of species diversity patterns and their underlying factors has been a continuing scientific inquiry for the past century (e.g., [1,2,3,4,5,6])
Our HOF model results found that most species (87% of 113 species) did not experience any steep abundance decline along the Florida peninsula when compared with their general trend across the range, suggesting that the observed diversity pattern of tree species in Florida could merely be a continuation of latitudinal diversity gradients in the southeastern United States, independent of peninsular geometry
Tree species richness showed a hump-shaped pattern along the latitudinal gradient in the eastern United States (US) with the highest (142 species) being around mid-range latitude
Summary
The study of species diversity patterns and their underlying factors has been a continuing scientific inquiry for the past century (e.g., [1,2,3,4,5,6]). The underlying mechanisms of LDG are generally well explained by various factors, including hypotheses based on environment [9], evolutionary factors [10], and history [11]; regional scale anomalies—in particular, the inverse LDG pattern found on peninsulas—remain unresolved [12]. Since the first observation of the decreasing diversity of bird species along the Florida peninsula [13], this monotonic pattern has attracted considerable attention over the past 60 years. Tree species in the Florida peninsula exhibit an inverse LDG pattern, such that the number of species within a defined area—i.e., species richness as a proxy for tree species diversity—decreases. The diversity pattern of woody plants has received little attention, these plants are among the most prominent organisms that sustain the biodiversity and functions of ecosystems
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