Periods of Inundation Show Subtle Shifts in the Food Web Structure of Ephemeral Floodplain Pans in a Protected Ramsar‐Declared Wetland System

Abstract

ABSTRACT Ephemeral wetland pans in savanna landscapes support highly dynamic food webs whose structure is closely governed by hydroperiod. In these systems, variation in inundation length influences predator establishment, basal resource availability and the strength of aquatic‐to‐terrestrial linkages. We used stable isotopes of consumers (including fish and macroinvertebrates) and basal resources to examine how trophic position, reliance on aquatic carbon and isotopic niche width varied across two contrasting hydroperiod states: high hydroperiod in the wet season and low hydroperiod in the late dry season in six ephemeral pans of the Kruger National Park, South Africa. We predicted that during the high hydroperiod, ephemeral pans would support more stratified trophic structures and stronger assimilation of aquatic basal resources. Our results showed that trophic positions were consistently higher and more stratified under high hydroperiod conditions, especially among predators and fish. In contrast, predators and fish showed lower, more overlapping trophic positions across consumer groups in low hydroperiods. Isotopic niche widths (as measured by standard ellipse area) showed inconsistent responses among pans, with some pans exhibiting wider niches during low hydroperiod conditions. This variation likely reflects the ecological heterogeneity and resource unpredictability characteristic of rapidly drying habitats. These results accentuate the sensitivity of ephemeral wetland food webs to hydrological fluctuations and provide a foundational case study for understanding trophic responses to changing hydroperiods in African savanna ecosystems.