Ecological Drivers of Biodiversity in Small Agricultural Wetlands

Abstract

Small seasonal wetlands are among the most widespread freshwater habitats in agricultural landscapes worldwide, yet they remain poorly integrated into biodiversity theory and conservation practice. This dissertation uses field surveys and satellite remote sensing across small seasonal ponds in western India to investigate how habitat structure, hydrological dynamics, and analytical choices jointly shape ecological patterns and conservation outcomes in these understudied ecosystems.The first study integrates powerful, but often disjunct concepts in ecology - foundation species ecology and species-area theory. We ask how habitat-forming vegetation and trophic identity modulate biodiversity–area relationships in waterbird communities. Ponds with greater vegetation cover—acting as foundation species (FS) that provide structural habitat—exhibited steeper species–area (SARs) and abundance–area relationships (AARs). In small ponds, however, high FS cover reduced richness and abundance, likely by eliminating open-water foraging space. Contrary to classical predictions, herbivores showed stronger area dependence than omnivores or carnivores, offering rare within-taxon evidence of trophic modulation of biodiversity–area scaling. These effects were strongest during the dry summer season, when vegetation likely provides critical refuge in a resource-scarce landscape. The second study examines how seasonal habitat contraction restructures trophic dominance within the same pond network. Using paired winter–summer surveys combined with satellite-derived water extent, we show that predator biomass density increased with habitat contraction while herbivores showed a vegetation-mediated occupancy response—a guild-level divergence consistent with trophic-selective aggregation rather than passive crowding. This links flood-pulse and predator-permanence frameworks in time rather than space, and offers a mechanistic basis for predicting trophic reorganization as climate change intensifies seasonal drawdown across human-modified landscapes. The third study addresses a practical question that runs through both empirical chapters: when do analytical choices about how to represent abundance data change conservation priorities? We fitted matched presence–absence, count, and ordinal models to 58 species–season combinations and compared the wetlands selected under a fixed conservation budget, supported by a simulation study spanning 360 ecological scenarios. Presence–absence data performed adequately when counts were near-binary or a strong shared environmental gradient drove both occurrence and abundance. Ordinal categories added genuine conservation value in roughly one quarter of scenarios, where baseline counts were moderate-to-high and spread across ordinal bins. Counts became non-negotiable when occurrence and abundance responded to opposing environmental drivers—a decoupling common among colonial breeders and seasonally flocking waterbirds—where presence–absence rankings could actively misdirect conservation resources. Together, these three studies reveal that biodiversity patterns in small wetlands are governed by the interplay of spatial extent, habitat structure, seasonal hydrology, and trophic identity—and that the analytical lens through which those patterns are measured can itself alter conservation outcomes. Integrating these ecological and methodological dimensions offers a more robust foundation for managing the small, seasonal wetlands that dominate agricultural landscapes globally.