Ecology of Gambusia affinis (Mosquitofish) along an agricultural land use gradient

Abstract

Invasive species pose a major threat to ecosystems all over the world, affecting both biodiversity and ecosystem functioning. Intensification of catchment land use is associated with degradation of rivers and streams via changes to physiochemical and habitat conditions. Understanding how land use change interacts with invasive species is important if the threat of invasives are to be managed effectively. This study examines how agricultural land use influences the distribution, life history traits and feeding ecology of an invasive fish – Gambusia affinis. Streams with and without G. affinis, lying in catchments along a gradient (0 – 97%) of agricultural land use were studied. The distribution of Gambusia was related to in-stream physiochemical and catchment scale gradients associated with agricultural development. Dietary ecology was evaluated using two common techniques: 1) Gut content analysis (GCA), and 2) stable isotope analysis (SIA). Agricultural development was associated with a decline in water quality, velocity and riparian cover and increases in channel macrophyte cover, sedimentation and water temperature. Gambusia abundance was positively associated with temperature, macrophyte cover and nutrients and negatively associated with stream velocity and riparian vegetation. The in-stream changes associated with agricultural development facilitated increased Gambusia abundance. Gambusia displayed a large degree of dietary plasticity, although where a preferred prey was present Gambusia tended to specialise. Diet variability was associated with both resource availability and ontogenetic development, with increasing body size related to increasing prey size. Gambusia shifted from a reliance on autochonous to allochthonous energy pools with growth, representing a shift in foraging behaviour. Agricultural land use is directly associated with changes to physiochemical, habitat and water quality components of streams, which negatively affects native communities. Agricultural land use can also facilitate the spread of an invasive species, putting native biota under further stress and potentially altering ecosystem functioning. Keywords: Gambusia affinis, Mosquitofish, land use gradient, agriculture, invasive species.