Niche partitioning among frugivorous fishes in response to fluctuating resources in the Amazonian floodplain forest

Abstract

In response to temporal changes in the quality and availability of food resources, consumers should adjust their foraging behavior in a manner that maximizes energy and nutrient intake and, when resources are limiting, minimizes dietary overlap with other consumers. Floodplains of the Amazon and its lowland tributaries are characterized by strong, yet predictable, hydrological seasonality, seasonal availability of fruits, seeds, and other food resources of terrestrial origin, and diverse assemblages of frugivorous fishes, including morphologically similar species of several characiform families. Here, we investigated how diets of frugivorous fishes in the Amazon change in response to fluctuations in food availability, and how this influences patterns of interspecific dietary overlap. We tested predictions from classical theories of foraging and resource competition by estimating changes in diet breadth and overlap across seasons. We monitored fruiting phenology to assess food availability, and surveyed local fish populations during three hydrological seasons in an oligotrophic river and an adjacent oxbow lake in the Colombian Amazon. We analyzed stomach contents and stable isotope data to evaluate temporal and interspecific relationships for dietary composition, breadth, and overlap. Diets of six species of characiform fishes representing three genera changed according to seasonal fluctuations in food availability, and patterns of diet breadth and interspecific overlap during the peak flood pulse were consistent with predictions of optimal foraging theory. During times of high fruit abundance, fishes consumed items to which their functional morphological traits seemed best adapted, potentially enhancing net energy and nutritional gains. As the annual flood pulse subsided and availability of forest food resources in aquatic habitats changed, there was not a consistent pattern of diet breadth expansion or compression. Nonetheless, shifts in both diet composition and stable isotope ratios of consumer tissues during this period resulted in trophic niche segregation in a pattern consistent with competition theory.

Isotopic variation among Amazonian floodplain woody plants and implications for food-web research

“…Fruiting phenology of most trees and liana species in flooded forests is synchronized with the annual flood (Parolin et al 2004). This resource pulse attracts a diverse suite of frugivores, from birds, bats and monkeys to turtles and fishes (Goulding 1980, Barnett et al 2005, Haugaasen & Peres 2007, 2008, Correa & Winemiller 2014. The high predictability of the flood pulse in the Amazon favors consumers capable of exploiting floodplain resources, therefore riparian terrestrial and aquatic food webs are subsidized by energy inputs from the flooded forest (Junk et al 1997, Oliveira et al 2006a, Junk & Piedade 2010.…”

Seasonal variation in fish trophic networks in two clear-water streams in the Central Llanos region, Venezuela

“…During the wet season, water bodies expand into floodplains where fishes can exploit habitats suitable for spawning, feeding, and refuge from predators (Winemiller, Jepsen, 1998). Aquatic floodplain habitats generally support high primary and secondary production and diverse resources, including allochthonous foods such as fruits, seeds, and terrestrial invertebrates (Goulding et al, 1988;Henderson, 1990;Correa, Winemiller, 2014). During the dry season, aquatic floodplain habitats shrink, fish densities increase within more permanent water bodies, and availability of many food resources declines (Winemiller, Jepsen, 1998).…”

“…In contrast, optimal foraging theory (Emlen, 1966;Schoener, 1971) would predict low dietary breadth with high overlap when resources are abundant and diverse allowing consumers select the most profitable food resources. These conditions may occur during the annual flood pulse in tropical river floodplains (Correa, Winemiller, 2014). Higher fish densities resulting from habitat compression during the low-water season generally increases the frequency of encounters between predatory fishes and their prey (Arrington et al, 2005), which should result in increased food web connectance (Winemiller, 1990;Winemiller et al, 2001).…”

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought

“…At such time lake fish can enter the adjacent flooded forest and feed on fruits, seeds, insects, and terrestrial invertebrates (Fernandes, 1997;Claro-Junior et al, 2004;Mérona and Rankin-de-Mérona, 2004;Noveras et al, 2010;Correa and Winemiller, 2014). In contrast, lakes diminish in depth and area during the low-water season, with a consequent decline in habitat and food availability.…”