Ecosystem Engineering by a Dominant Detritivore in a Diverse Tropical Stream

Abstract

Prochilodus mariae (Characiformes: Prochilodontidae) is a detritivorous fish distributed throughout the Orinoco river basin of South America. Spectacular migrations of these fishes occur at the end of the rainy season into the Andean foothills. Prochilodus ingest large quantities of sediments and may thereby modify habitats in neotropical streams. The major objectives of this study were (1) to explore experimentally the importance of Prochilodus in structuring a tropical stream in the Venezuelan Andean piedmont, and (2) to determine whether there was sufficient ecological redundancy in a diverse and abundant assemblage of epibenthic fishes to compensate for the removal of Prochilodus. Community structure was compared among three experimental treatments: (1) Prochilodus exclusion, (2) Prochilodus enclosure, and (3) the natural fish assemblage. Selective exclusion of Prochilodus resulted in striking changes in community structure as measured by patterns of sediment accrual and the composition of algal and invertebrate assemblages. Highly significant increases in total dry mass and in ash—free dry mass of sediments accruing on stream—bottom substrates were observed almost immediately following the exclusion of Prochilodus. Moreover, the composition of algal and invertebrate assemblages was significantly modified by Prochilodus. Taxa such as diatoms were reduced in number when Prochilodus was present; in contrast, Prochilodus appeared to facilitate nitrogen—fixing cyanobacteria. Total invertebrate densities were greatest in the Prochilodus removal treatment; however, a variety of responses to the experimental treatments was observed among different taxa analyzed individually, including density reductions, increases, and no measurable effects. This study suggests that the detritivore Prochilodus is a functionally dominant species in Andean foothill streams via sediment—processing activities. Moreover, it provides little evidence to support the notion that strongly interacting species are limited to simple systems with few food web components.

Fish extinctions alter nutrient recycling in tropical freshwaters

“…Moreover, experimental manipulations in both RLM and LT suggest that compensatory responses may not always occur in a predictable fashion. For example, consumptive effects of large algivorous and detritivorous fish cannot be replaced by smaller fish or other taxa (10,17,35), and the same probably applies to large predators (8). Thus, certain extinctions may have disproportionately strong effects on ecosystems by eliminating species that play unique roles within functional groups.…”

“…However, they differ markedly in size, physical structure, and fish community composition, thereby enhancing the inferential power offered by concordant results. Further details about each site are available elsewhere (10,(17)(18)35).…”

Bed disturbance via foraging fish increases bedload transport during subsequent high flows and is controlled by fish size and species

“…Amongst these, foraging by fish is a potentially widespread and effective zoogeomorphic activity, but very little work has explored this possibility. Some work has considered the impact of detrivorous, tropical fish on fine sediment accrual within lotic systems (Flecker, 1996;1997;Flecker and Taylor, 2004), finding that foraging reduced sediment accrual (Bowen et al, 1984;Lopez and Levington, 1987;Vari, 1989;Flecker, 1992) and that the effect increased with species density (Bowen, 1983;Goulding et al,1988). European Cyprinid species reduce fine sediment accrual within lotic and lentic environments.…”

Influence of temperature on surface sediment disturbance by freshwater fish: a microcosm experiment

“…Among this fauna, many studies have focused on fish as actors of bed surface disturbance in streams (e.g., Flecker, 1996;Flecker and Taylor, 2004;Holtgrieve and Schindler, 2010), given their key role in the flux and transfer of particles and solutes in aquatic ecosystems. The influence of spawning behaviour of salmonid species on streambed has been extensively documented (e.g., Montgomery et al, 1996;Peterson and Foote, 2000;Gottesfeld et al, 2004;Moore et al, 2007;De Vries, 2012) but knowledge of other behaviours as zoogeomorphic activity (e.g., foraging, swimming and burrowing) remains scarce, especially for non-salmonid species (but see Statzner and Sagnes, 2008;Shirakawa et al, 2013;Pledger et al, 2014).…”