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...

Abstract. We evaluate a three‐part hypothesis explaining why gall‐inducing insect species richness is so high in scleromorphic vegetation: (1) persistence of low nutrient status scleromorphic leaves facilitates the galling habit in warm temperate latitudes; (2) favourable colonization sites for gallers result from reduced hygrothermal stress, high phenolics in the outer cortex of the gall, and reduced carnivore and fungal attack in the gall; and (3) in more mesic sites, mortality is high due to carnivore attack and invasion of galls by fungi. Over 280 samples of local species of galling herbivorous insects from fourteen countries on all continents except Antarctica revealed a strong pattern of highest richness in warm temperate latitudes, or their altitudinal equivalents. The peak of galling species richness on the latitudinal gradient from the equator into the Arctic was between 25 to 38° N or S. Galling species were particularly diverse in sclerophyllous vegetation, which commonly had greater than twelve species per local sample. In mesic, non‐sclerophyllous vegetation types the number of galling species was lower with twelve or fewer species present. Many sites in sclerophyllous vegetation supported between thirteen and forty‐six galling species locally, including campina islands in Amazonia, cerrado savanna in central Brazil, the Sonoran Desert in Arizona and Mexico, shrubland in Israel, fynbos in South Africa and coastal scleromorphic vegetation in Australia. At the same latitude, or its elevational equivalent, galling species richness was significantly higher in relatively xeric sites when compared to riparian or otherwise mesic habitats, even when scleromorphic vegetation dominated the mesic sites. The results were consistent with the hypothesis and extend to a more general level the patterns and predictions on the biogeography of gall‐inducing insects.

Quantifying the spatio-temporal distribution of arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest arthropods.

Heterospecific neighbors may reduce damage to a focal plant by lowering specialist herbivore loads (associational resistance hypothesis), or enhance damage by increasing generalist herbivore loads (associational susceptibility hypothesis). We tested the associational effects of tree diversity on herbivory patterns of the tropical focal tree Tabebuia rosea in an experimental plantation setup, which contained tree monocultures and mixed stands. We found higher herbivore damage to T. rosea at higher tree diversity, indicating that T. rosea did not benefit from associational resistance but rather experienced associational susceptibility. The specific consideration of the two dominant insect herbivore species of T. rosea, the specialist chrysomelid Walterianella inscripta and the specialist pyralid Eulepte gastralis, facilitated understanding of the detected damage patterns. Tree diversity exerted opposite effects on tree infestation by the two herbivores. These findings point to resource concentration effects for the chrysomelid beetle (favored by tree monoculture) and to resource dilution effects for the pyralid caterpillar (favored by tree mixture) as underlying mechanisms of herbivore distribution. A strong contribution of the pyralid to overall damage patterns in diversified stands suggests that associational susceptibility may not necessarily be related to higher abundances of generalist herbivores but may also result from specialized herbivores affected by resource dilution effects. Thus, the identity and biology of herbivore species has to be taken into account when attempting to predict damage patterns in forest ecosystems.

The abundance, activity and species richness of arthropods, particularly of insect herbivores, were investigated in the upper canopy and understorey of a lowland rainforest at La Makande, Gabon. In total 14 161 arthropods were collected with beating, flight interception and sticky traps, from six canopy sites, during the day and at night, from midJanuary to mid-March 1999. The effects of stratum were most important, representing between 40 and 70% of the explained variance in arthropod distribution. Site effects represented between 20 and 40% of the variance and emphasized the need for replication of sampling among canopy sites. Time effects (diel activity) explained a much lower percentage of variance (6-9%). The density and abundance of many arthropod taxa and species were significantly higher in the upper canopy than in the understorey. Arthropod activity was also higher during the day than at night. In particular, insect herbivores were 2.5 times more abundant and twice as speciose in the upper canopy than in the understorey, a probable response to the greater and more diverse food resources in the former stratum. Faunal overlap between the upper canopy and understorey was low. The most dissimilar herbivore communities foraged in the understorey at night and the upper canopy during the day. Further, a taxonomic study of a species-rich genus of herbivore collected there (Agdus, Coleoptera Buprestidae) confirmed that the fauna of the upper canopy was different, diverse and very poorly known in comparison to that of the understorey. Herbivore turnover between day and night was rather high in the upper canopy and no strong influx of insect herbivores from lower foliage to the upper canopy was detected at night. This suggests that insect herbivores of the upper canopy may be resident and well adapted to environmental conditions there.