Functional trait responses of aquatic macroinvertebrates to simulated drought in a Neotropical bromeliad ecosystem

Abstract

Summary The duration of the dry seasons in south‐eastern Amazonia is expected to increase. Little is known of how freshwater assemblages respond to drought in the humid rainforests and of the extent to which they resist the absence of rainfall before the collapse of the system. We manipulated rainshelters over tank‐forming bromeliads (i.e. the interlocking leaf axils of these plants form wells that collect rainwater) to simulate an exceptionally long dry period (49 days, compared with a 10‐year mean ± SD annual maximum number of 17 ± 5.3 days without rainfall at the study site) and then a rewetting period. By sampling weekly over 3 months, we followed the dynamics of the representation of abundance‐weighted traits in invertebrate assemblages in these treatment plants and in a control group. The functional structure of assemblages was drought resistant until the water volume in the bromeliad pools dropped by 90%, when there was a sudden shift in the functional trait structure due to the loss of most populations except the drought‐resistant culicids. Traits related to life history, body size and preferred food showed significant responses to drought. There was a convergence in the functional traits of species surviving in dry plants, strengthening the idea that environmental filtering, rather than stochasticity, determines the functional trajectory of aquatic assemblages during drought. At the end of the dry period, samples of the detritus potentially containing drought‐resistant eggs/cysts (and eventually live larvae) were taken from the dry plants and rewetted in the laboratory, allowing us to distinguish resistant species from those requiring recolonisation via subsequent oviposition by adults from elsewhere. Patches of water‐filled bromeliads persisting in the area provided the most important pool of colonists, and communities returned to the pre‐disturbance state within 1–2 weeks of rewetting. Our results suggest that the functional trait structure of invertebrate assemblages in bromeliads could remain stable under scenarios of precipitation change that would triple the duration of current dry periods at a local scale. Future experiments should evaluate how environmental factors might alter the tipping point between resistance to drought and a collapse in ecosystem processes.

Variación temporal de la diversidad taxonómica y rasgos funcionales de los macroinvertebrados acuáticos en ríos temporales en la isla de Providencia, Colombia

“…Esta resistencia se atribuye a la presencia de estructuras tales como branquias (Dero, Ancylidae Mf., Pyrgophorus), conchas para proteger el cuerpo o pigmentos como la hemoglobina (Chironomus), así como de mecanismos especializados que les permiten salvaguardarse de dichas condiciones. Estas formas de especialización de los macroinvertebrados ante las condiciones físicas y químicas adversas encontradas en la isla de Providencia concuerdan con lo hallado para ríos intermitentes de Australia, España y Estados unidos (Beche et al 2006, Bonada et al 2007, Dézerald et al 2015, Huryn et al 2008, Stubbington et al 2016). …”

“…Los rasgos que predominan varían dependiendo de si la sequía es estacional predecible o si es un evento impredecible (Bogan et al 2015, Lake 2003. En general, se ha encontrado en ecosistemas mediterráneos y templados que los rasgos funcionales asociados con mayor adaptación a la temporalidad son: ciclos vitales flexibles (sincronización de los ciclos de vida acuáticos con las temporadas de lluvias), desarrollo ligado con la temperatura del agua, diapausa, huevos protegidos contra la desecación y alto poder de dispersión (Bonada et al 2007, Boulton 1989, Dézerald et al 2015, Dole-Olivier et al 1997, Lake 2003, McDonough et al 2011, Stubbington et al 2016, Williams y Hynes 1977, así como alimentación de tipo generalista (Dieterich y Anderson 2000).…”

“…En cambio, en la época de lluvias, prevalecieron organismos con ciclos de vida de más de un año, con menos de una generación por año; este tipo de ciclo corresponde a lento estacional y es propio de Laccophilus, entre otros. Estos patrones concuerdan con lo registrado por Bogan et al (2015) y Dézerald et al (2015) para ríos intermitentes de Europa.…”

Assessing the role of canopy cover on the colonization of phytotelmata by aquatic invertebrates: an experiment with the tank-bromeliad Aechmea lingulata

“…Beyond values of light intensity and temperature of stored water, canopy cover influenced only the amount of CPOM in bromeliads. However, the volume of water and the amount of FPOM, which are important variables for the colonization process (Kitching, 2000;Armbruster et al, 2002;Dézerald et al, 2015b), did not differ between treatments and contributed to the high similarity of the communities sampled throughout the experiment. These results differ from those found in studies developed in tropical forest ecosystems (Montero et al, 2010;González et al, 2014) and are probably related to the characteristics of restinga (i.e., less dense vegetation composed of species adapted to low water availability and high temperatures and solar radiation) (Zaluar and Scarano, 2000;Scarano, 2002).…”

“…Some studies have suggested the volume of water is the main factor that influences the colonization of phytotelm ecosystems because it determines habitat size and susceptibility to colonization (Srivastava et al, 2008;Dézerald et al, 2014;Gossner et al, 2016). Although unshaded bromeliads have higher capacity of water collection (Déz-erald et al, 2014), tanks held by these plants are also subject to higher evaporation rates as a result of direct exposure to solar radiation (Dézerald et al, 2015b;Buosi et al, 2015). In this study, the volumes of stored water differed only between colonization times and were related to rainfall values during the experiment.…”