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Drought attenuates the impact of fish on aquatic macroinvertebrate richness and community composition.

ABSTRACT: Identifying ecological niche filters that shape species community composition is a critical first step in understanding the relative contributions of deterministic and stochastic processes in structuring communities. Systems with harsh ecological filters often have a more deterministic basis to community structure. Although these filters are often treated as static, investigations into their stability through time are rare, particularly in combination with extreme forms of environmental change such as drought.We examined the richness and composition of aquatic macroinvertebrate communities from 36 ponds over four years during the onset of a megadrought to answer the following questions: (1) what are the relative influences of non-native fish presence and pond permanence in structuring communities? And (2) how do the magnitudes of such filters vary through time?As predicted, fish presence had a strong, negative effect on both alpha and gamma diversity, lowering average invertebrate richness in pond communities by 23%. However, fish presence and sample year interacted to determine both richness and taxa composition: as drought conditions intensified, the effects of fish weakened such that there were no differences in the richness or composition between fish and fishless ponds by the later sampling years. Moreover, large-bodied invertebrate groups - often considered highly vulnerable to fish predation - were detected within fish-occupied sites by the final year of the study.This pattern was associated with progressive decreases in precipitation due to a severe drought in California, emphasizing the importance of exogenous, regional factors in moderating the strength of biotic niche filters on local community structure over time. Given that all detected fish species were non-native, these results also have application to understanding and forecasting changes in the diversity of native insects and other aquatic invertebrates.

SUBMITTER: McDevitt-Galles T

PROVIDER: S-EPMC6405237 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Project description:In Costa Rica, considerable effort goes to conservation and protection of biodiversity, while at the same time agricultural pesticide use is among the highest in the world. Several protected areas, some being wetlands or marine reserves, are situated downstream large-scale banana farms, with an average of 57 pesticide applications per year. The banana industry is increasingly aware of the need to reduce their negative environmental impact, but few ecological field studies have been made to evaluate the efficiency of proposed mitigation strategies. This study compared the composition of benthic macroinvertebrate communities up- and downstream effluent water from banana farms in order to assess whether benthic invertebrate community structure can be used to detect environmental impact of banana farming, and thereby usable to assess improvements in management practises. Aquatic invertebrate samples were collected at 13 sites, using kick-net sampling, both up- and downstream banana farms in fast flowing streams in the Caribbean zone of Costa Rica. In total, 2888 invertebrate specimens were collected, belonging to 15 orders and 48 families or taxa. The change in community composition was analysed using multivariate statistics. Additionally, a biodiversity index and the Biological Monitoring Working Party (BMWP) score system was applied along with a number of community composition descriptors. Multivariate analyses indicated that surface waters immediately up- and downstream large-scale banana farms have different macroinvertebrate community compositions with the most evident differences being higher dominance by a single taxa and a much higher total abundance, mostly of that same taxon. Assessment of macroinvertebrate community composition thus appears to be a viable approach to detect negative impact from chemical-intensive agriculture and could become an effective means to monitor the efficacy of changes/proposed improvements in farming practises in Costa Rica and similar systems.

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Drought attenuates the impact of fish on aquatic macroinvertebrate richness and community composition.

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