Why are there so many species in the tropics?

Abstract

Known for centuries, the geographical pattern of increasing biodiversity from the poles to the equator is one of the most pervasive features of life on Earth. A longstanding goal of biogeographers has been to understand the primary factors that generate and maintain high diversity in the tropics. Many ‘historical’ and ‘ecological’ hypotheses have been proposed and debated, but there is still little consensus. Recent discussions have centred around two main phenomena: phylogenetic niche conservatism and ecological productivity. These two factors play important roles, but accumulating theoretical and empirical studies suggest that the single most important factor is kinetics: the temperature dependence of ecological and evolutionary rates. The relatively high temperatures in the tropics generate and maintain high diversity because ‘the Red Queen runs faster when she is hot’.

Spatial variation of mammal richness, functional and phylogenetic diversity in the Mexican transition zone

“…In a global study, Oliveira et al (2016) found evidence showing that mammal species richness and functional diversity are decoupled in America, with species richness being explained by environmental factors (equilibrium processes), whilst functional diversity is related to evolutionary time (non-equilibrium processes). Our results agree with these findings, and also with the general pattern of species richness increase towards the tropics (Rosenzweig 1995, Brown 2014. Functional diversity in the Mexican Transitional Zone is weakly explained by environmental factors, which suggest that non-equilibrium dynamics may be driving the community structuring, according to the intrinsic characteristics of our study area.…”

“…At regional scales, seasonality, productivity and climatic stress have resulted significant indicators of biodiversity variation (Brown 2014). In this study, S has a marginal relationship with net primary productivity, PD is not related to any of the abiotic variables we tested and FD is weakly explained by the area, and environmental heterogeneity (variation in altitude and temperature seasonality).…”

Hidden diversity in forest soils: Characterization and comparison of terrestrial flatworm’s communities in two national parks in Spain

“…in preparation ); nonetheless, this is still poor when compared to the more than 119 and 98 recorded species from São Paulo and Florianopolis only in Brazil (Sluys, 1999). These figures simply confirm the known rule that species richness is much higher in the tropics than in temperate and cold regions (Brown, 2014), being terrestrial planarians one more example to certify this fact. Nevertheless, our results confirm another rule stating that there is a very large bias in species descriptions according to the number of taxonomists dedicated to the group: Since we started working on species identification in Europe, we have seen that the number of species has increased rapidly.…”

Population biology and morphometric sexual maturity of the fiddler crab Uca (Uca) maracoani (Latreille, 1802) (Crustacea: Decapoda: Ocypodidae) in a semiarid tropical estuary of northeastern Brazil

“…maracoani population studied in Brazil (Table 3). In fact, subtropical populations are known to be more numerous than tropical ones (Brown, 2014). However, it is important to keep in mind that that the number of collectors and the sampled area are not the same among the previous studies, which can generate bias in the comparisons.…”