ABSTRACT
Worldwide, land use changes and urbanization affect habitat and biota in streams, drastically disrupting environmental conditions and biotic interactions. We evaluated the trophic ecology of the tolerant fish Corydoras paleatus in a prairie stream with contrasting environmental conditions intimately aligned with different nearby land uses. Gut analyses was conducted at three stream reaches with contrasting ecological attributes regarding water quality, habitat structure and riparian condition. A total of 231 guts were analyzed and 15 prey items identified. A significant variation in composition and structure of the dietary assemblage, niche breadth and feeding patterns of C. paleatus under different environmental conditions was observed. Psychodidae prevailed in most deteriorated environmental conditions and Chironomidae, followed by nematodes, in stream reaches where environmental conditions improved. Maximum niche breadth and a larger proportion of generalist individuals were found at the most deteriorated site. Conversely, the proportions of specialized individuals were slightly higher at sites with better ecological conditions. Psychodidae and mineral fragments were positively correlated with the most detrimental conditions, while filamentous algae prevailed where these conditions improved. Overall, good evidence suggesting that trophic ecology of a tolerant species is affected by local environmental conditions in water quality, habitat structure and riparian corridor was observed.
Subject(s)
Grassland , Invertebrates , Animals , Ecosystem , Fishes , Humans , PlantsABSTRACT
The relationship between the timing of recurrent biological events and seasonal climatic patterns (i.e., phenology) is a crucial ecological process. Changes in phenology are increasingly linked to global climate change. However, current evidence of phenological responses to recent climate change is subjected to substantial regional and seasonal biases. Most available evidence on climate-driven phenological changes comes from Northern Hemisphere (NH) ecosystems and typically involves increases in spring and summer temperatures, which translate into earlier onsets of spring population developments. In the Argentine Pampa region, warming has occurred at a much slower pace than in the NH, and trends are mostly restricted to increases in the minimum temperatures. We used zooplankton abundance data from Lake Chascomús (recorded every two weeks from 2005 to 2015) to evaluate potential changes in phenology. We adopted a sequential screening approach to identify taxa displaying phenological trends and evaluated whether such trends could be associated to observe long-term changes in water temperature. Two zooplankton species displayed significant later shifts in phenology metrics (end date of Brachionus havanaensis seasonal distribution: 31 day/decade, onset and end dates of Keratella americana seasonal distribution: 59 day/decade and 82 day/decade, respectively). The timing of the observed shift in B. havanaensis phenology was coincident with a warming trend in the May lake water temperature (4.7°C per decade). Analysis of abundance versus temperature patterns from six additional shallow Pampean lakes, and evaluation of previous experimental results, provided further evidence that the lake water warming trend in May was responsible for the delayed decline of B. havanaensis populations in autumn. This study is the first report of freshwater zooplankton phenology changes in the Southern Hemisphere (SH).
