No effects of macroconsumer exclusion on macroinvertebrate functional composition in Brazilian karst streams along a gradient of riparian forest loss

Degradation and loss of riparian vegetation are some of the main drivers of change in the trophic interactions among aquatic macroconsumers. These changes can often have major consequences for biodiversity and stream ecosystem functioning. Yet, many aspects of food-web dynamics are still not well understood, including how food webs among tropical streams respond to riparian vegetation loss. We examined the role of macroconsumers on community structure of functional feeding groups of benthic macroinvertebrates along a forest cover gradient within the Bodoquena Plateau, Brazil. We compared the effect of excluding macroconsumers (using electric fences) on functional feeding groups to those in controls within seven karst streams along a gradient of riparian vegetation cover. Aquatic insect and gastropod communities were dominated by groups of collector-gatherers, scrapers, and predators across all sites. The exclusion of macroconsumers did not lead to an increase in the abundance of macroinvertebrates and was not affected by the forest cover during the experiment. These findings demonstrated that the experimental exclusion of macroconsumers resulted in a lack of or negligible effect on functional feeding groups along the gradient of forest cover. It is important to consider the specificity of trophic relationships to fully understand the effects of vegetation loss on streams where complex groundwater hydrology can also affect food webs such as in karst terrain.Abstract in Portuguese is available with online material. A degradacao e a perda da vegetacao riparia e um dos principais impulsionadores de mudancas nas interacoes troficas entre os macroconsumidores aquaticos. Essas mudancas podem ter graves consequencias para a biodiversidade e para o funcionamento dos ecossistemas de corrego. Entretanto, muitos aspectos da cadeia trofica ainda nao sao bem compreendidos, incluindo como as redes troficas nos corregos respondem a perda da vegetacao riparia. Nesse trabalho, avaliamos o papel dos macroconsumidores na estrutura e na funcao dos grupos funcionais de alimentacao dos macroinvertebrados ao longo de um gradiente de cobertura de vegetacao riparia no Planalto da Bodoquena. Comparamos o efeito da exclusao dos macroconsumidores (usando cerca eletrica) nos grupos funcionais, comparado ao tratamento controle em sete corregos carsticos ao longo do gradiente de vegetacao. Comunidades de insetos e gastropodes aquaticos foram dominados por grupos de coletores, raspadores e predadores ao longo dos sitios de coleta. A exclusao dos macroconsumidoes nao aumentou a abundancia dos macroinvertebrados e nao foi afetado pela cobertura de floresta durante o experimento. Esses achados demostram que a exclusao experimental resultou em um fraco ou insignificante efeito nos grupos funcionais ao longo do gradiente de vegetacao. e importante considerar a especificidade das relacoes troficas para entender os efeitos da perda da vegetacao nos corregos, especialmente onde a complexa hidrologia carstica pode tambem afetar as redes troficas. Manipulating the presence of macroconsumers did not induce effects on the abundance of the functional feeding groups of the benthic invertebrates along the forest cover gradient in the Brazilian karst streams.image