Abstract

Insects and vertebrates collectively dominate animal biodiversity, yet they exhibit fundamentally different patterns of species richness, distribution, and vulnerability to environmental change. This review synthesizes current knowledge on species richness patterns across terrestrial, freshwater, and marine ecosystems, examining the ecological determinants that shape insect and vertebrate distributions. Tropical forests harbor the highest overall diversity for both groups, but insects dominate species counts in all ecosystems, with estimates suggesting that insects comprise 75-85% of animal species globally while vertebrates represent less than 5%. Latitudinal diversity gradients are pronounced for vertebrates but show greater variability among insect taxa, with some hyperdiverse groups exhibiting weak or even inverse gradients. Altitudinal patterns generally peak at mid-elevations, though insects often show broader elevational ranges than vertebrates. Ecological determinants—climate energy, habitat heterogeneity, productivity, disturbance regimes, and evolutionary history—operate across scales to shape diversity patterns, with insects responding more strongly to microhabitat variation and vertebrates to landscape-scale factors. Comparative analysis reveals that insects' shorter generation times, higher reproductive rates, and greater dispersal ability facilitate rapid responses to environmental change, while their enormous diversity and functional importance demand urgent conservation attention despite persistent data gaps. Anthropogenic pressures including habitat loss, climate change, pollution, and overexploitation threaten both groups, but insects face additional risks from pesticide exposure and light pollution that remain poorly addressed in conservation frameworks. Future research must prioritize understudied tropical and freshwater systems, integrate remote sensing with biodiversity modeling, and leverage community science to address critical knowledge gaps and inform evidence-based conservation strategies.