Arthropod Diversity in a Tropical Forest

Abstract

Most eukaryotic organisms are arthropods. Yet, their diversity in rich terrestrial ecosystems is still unknown. Here we produce tangible estimates of the total species richness of arthropods in a tropical rainforest. Using a comprehensive range of structured protocols, we sampled the phylogenetic breadth of arthropod taxa from the soil to the forest canopy in the San Lorenzo forest, Panama. We collected 6144 arthropod species from 0.48 hectare and extrapolated total species richness to larger areas on the basis of competing models. The whole 6000-hectare forest reserve most likely sustains 25,000 arthropod species. Notably, just 1 hectare of rainforest yields >60% of the arthropod biodiversity held in the wider landscape. Models based on plant diversity fitted the accumulated species richness of both herbivore and nonherbivore taxa exceptionally well. This lends credence to global estimates of arthropod biodiversity developed from plant models.M ost eukaryote species are terrestrial arthropods (1), and most terrestrial arthropods occur in tropical rainforests (2). However, considerably greater sampling effort is required in tropical arthropod surveys to yield realistic estimates of global species richness (3-7). A basic hindrance to estimating global biodiversity lies in a lack of empirical data that establish local biodiversity, which can be scaled up to achieve a global estimate.Although many studies reported species richness for selected groups of well-studied insect taxa, no satisfactory estimate of total arthropod species richness exists for a single tropical rainforest location to date.The unstructured collection and small-scale survey of tropical arthropods cannot yield convincing estimates of total species richness at a specific forest (7-9). Most studies either target few arthropod orders or trophic guilds, or use a limited array of sampling methods, or ignore the diverse upper canopy regions of tropical forests (10-15). Moreover, sampling protocols have rarely been structured in such a way that, with increased sampling, incomplete data on local diversity (7) can be extrapolated to estimate total species richness across multiple spatial scales (16). Where such structured estimates are made, it is invariably for insect herbivores on their host plants (5). However, species accumulation rates may differ markedly for nonherbivore guilds, which include more than half of all described arthropod species (1, 17). As the degree of host specificity (effective specialization) of other guilds can be much lower than that of insect herbivores, or may be driven by different factors (18,19), global estimates based on herbivores alone are questionable. Consequently, extensive cross-taxon surveys with structured protocols at reference sites may be the only effective approach toward estimating total arthropod species richness in tropical forests (3).To provide a comprehensive estimate of total arthropod species richness in a tropical rainforest, we established a collaboration involving 102 researchers with expertise encom...

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“…This hyperdiversity of trees has been partially explained by the Janzen-Connell model 4,5 , which hypothesizes that host-specific predators and parasites reduce plant population growth in a density-dependent manner 6,7 . Sampling up in the tree canopies and below on the ground has further led to the view that arthropods are the most diverse eukaryotes in tropical rainforests 8,9 .The focus on eukaryotic macroorganisms in these studies is primarily because they are familiar and readily observable to us. We do not know whether the less familiar and less readily observable protists-microbial eukaryotes that are not animals, plants or fungi 10 -inhabiting these same ecosystems exhibit similar diversity patterns.…”

“…This hyperdiversity of trees has been partially explained by the Janzen-Connell model 4,5 , which hypothesizes that host-specific predators and parasites reduce plant population growth in a density-dependent manner 6,7 . Sampling up in the tree canopies and below on the ground has further led to the view that arthropods are the most diverse eukaryotes in tropical rainforests 8,9 .…”

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