Contrasting Effects of Leaf Litter Quality and Diversity on Oviposition of Mosquitoes.

The quality and diversity of leaf litter are important variables in determining the availability of energy in detritus-based food webs. These factors can be represented by the stoichiometric proportion between carbon and multiple nutrients, and the mixture of litter from different taxonomic and/or functional origins. In aquatic ecosystems, factors that accelerate litter decomposition can influence the secondary productivity of planktonic microbiota, which act as a link between litter and higher trophic levels. This study aimed to analyze the influence of litter quality and diversity on the oviposition behavior of medically important mosquitoes. We hypothesized that both factors would have a positive effect on the attraction of female mosquitoes and would stimulate a greater amount of oviposition. To test this hypothesis, microcosms containing isolated leaf litter leachates from four plant species were used to manipulate gradients of litter quality, and microcosms with all leachates combined were used to test the effects of litter diversity. The results showed a positive effect of litter quality (p < 0.05) on mosquito oviposition rate, with lower C:P ratio litter species (high-quality litter) presenting higher oviposition rates than litter species with high C:P ratios (low-quality litter). However, contrary to our expectations, litter diversity had a negative effect (p = 0.002) on the magnitude of egg-laying by mosquitoes. Our results highlight the importance of litter quality and diversity for insect reproductive behavior. Our data shows that litter quality can serve as a crucial indicator of a suitable environment utilized by female mosquitoes for oviposition. This finding can enhance our ability to understand and develop effective methods for mitigating the reproduction of medically significant mosquitoes, whether by allowing us to predict, based on the composition of vegetation species, areas more prone to mosquito infestation, or by using high-quality litter in oviposition traps. Furthermore, maintaining vegetation diversity can help control mosquito reproduction.

Prey defence phenotype mediates multiple-predator effects in tri-trophic food webs.

The emphasis on mechanisms governing the interaction among predators (e.g. cooperation, competition or intraguild predation) has driven the understanding of multiple-predator effects on prey survival and dynamics. However, overwhelming evidence shows that prey can adaptively respond to predators, exhibiting multiple defensive phenotypes to cope with predation. Nevertheless, there is still a relatively scarce theory connecting the emergence of prey defences in complex multi-predator scenarios and their ecological consequences. Using a mathematical approach, we evaluated the prevalence of defended prey phenotypes as a function of predator-induced mortality in a two-predator system, and how prey and phenotype dynamics affect trophic cascades. We also evaluated such responses when prey manifests a general defence against both predators (i.e. risk reducing) or a specialized defence against one predator at the expense of defence against the other predator (i.e. risk trade-off), and when such phenotypes induce fitness and foraging costs. We showed that the emergence of defended phenotypes under multiple predators depends on predator-induced mortality rates, the magnitude of phenotype costs and the effect of the defensive phenotype on the performance of all predators. Risk-reducing phenotypes enhance prioritized responses to predators with high killing rates, but prioritized responses are diminished when prey manifest risk trade-off phenotypes. Finally, we showed that resource abundance across the predation gradient directly depends on the prevalence of certain prey phenotypes and their effect on foraging costs. Ultimately, our results depict the implications of prey defences on prey and basal resources abundance in a multiple predators' environment, highlighting the role of the identity of defensive strategies in mediating the strength and nature of trophic cascades, via consumptive or non-consumptive effects.

A ênfase nos mecanismos que governam a interação entre predadores (por exemplo, cooperação, competição ou predação intra-guilda) tem impulsionado a compreensão dos efeitos de múltiplos predadores na sobrevivência e dinâmica de presas. No entanto, fortes evidências mostram que as presas podem responder de forma adaptativa aos predadores, exibindo vários fenótipos de defesa para lidar com a predação. No entanto, ainda há uma teoria relativamente escassa conectando a manifestação de defesas em presas em cenários com múltiplos predadores e suas consequências ecológicas. Usando uma abordagem matemática, avaliamos a prevalência de fenótipos de defesa de presas em função da mortalidade induzida por predadores em um sistema de dois predadores, e como a dinâmica de presas e dos fenótipos afeta a cascata trófica. Também avaliamos tais respostas quando a presa manifesta uma defesa geral contra ambos os predadores (ou seja, redução de risco) ou uma defesa especializada contra um predador em detrimento da defesa contra o outro predador (ou seja, trade-off de risco), e quando tais fenótipos induzem custos ao fitness e ao forrageamento. Nós mostramos que a manifestação de fenótipos de defesa sob múltiplos predadores depende das taxas de mortalidade induzidas pelo predador, da magnitude dos custos do fenótipo e do efeito do fenótipo no desempenho dos predadores. Os fenótipos de redução de risco aumentam as respostas priorizadas aos predadores com altas taxas de predação, mas as respostas priorizadas são reduzidas quando as presas manifestam fenótipos de trade-off de risco. Finalmente, mostramos que a abundância de recursos ao longo do gradiente de predação depende diretamente da prevalência de determinados fenótipos e seus efeitos no forrageamento da presa. Em última análise, nossos resultados retratam as implicações das defesas contra predadores na abundância de presas e recursos basais em um ambiente com múltiplos predadores, destacando o papel da identidade de estratégias de defesa na mediação da força e natureza das cascatas tróficas, via efeitos de consumo ou comportamentais.

Precipitation, landscape properties and land use interactively affect water quality of tropical freshwaters.

Globally, conversion of pristine areas to anthropogenic landscapes is one of the main causes of ecosystem service losses. Land uses associated with urbanization and farming can be major sources of pollution to freshwaters promoting artificial inputs of several elements, leading to impaired water quality. However, how the effects of land use on freshwater quality are contingent on properties of the local landscape and climate is still poorly understood. The aim of this study was to evaluate the effects of landscape properties (morphometric measurements of lakes and their catchments), precipitation patterns, and land use properties (extent and proximity of the land use to freshwaters) on water quality of 98 natural lakes and reservoirs in northeast Brazil. Water quality impairment (WQI) was expressed as a composite variable incorporating parameters correlated with eutrophication including nitrogen (N), phosphorus (P) and Chlorophyll-a concentration. Regression tree analysis showed that WQI is mainly related to highly impacted "buffer areas". However, the effects of land use in these adjacent lands were contingent on precipitation variability for 13% of waterbodies and on surface area of the buffer in relation to the volume of waterbody (BA:Vol) for 87% of waterbodies. Overall, effects on WQI originating from the land use in the adjacent portion of the lake were amplified by high precipitation variability for ecosystems with highly impacted buffer areas and by high BA:Vol for ecosystems with less impacted buffer areas, indicating that ecosystems subjected to intense episodic rainfall events (e.g. storms) and higher buffer areas relative to aquatic ecosystem size (i.e. small waterbodies) are more susceptible to impacts of land use. Land use at the catchment scale was important for the largest ecosystems. Thus, our findings point toward the need for considering a holistic approach to managing water quality, which includes watershed management within the context of climate change.

Effects of seasonality, trophic state and landscape properties on CO2 saturation in low-latitude lakes and reservoirs.

The role of tropical lakes and reservoirs in the global carbon cycle has received increasing attention in the past decade, but our understanding of its variability is still limited. The metabolism of tropical systems may differ profoundly from temperate systems due to the higher temperatures and wider variations in precipitation. Here, we investigated the spatial and temporal patterns of the variability in the partial pressure of carbon dioxide (pCO2) and its drivers in a set of 102 low-latitude lakes and reservoirs that encompass wide gradients of precipitation, productivity and landscape properties (lake area, perimeter-to-area ratio, catchment size, catchment area-to-lake area ratio, and types of catchment land use). We used multiple regressions and structural equation modeling (SEM) to determine the direct and indirect effects of the main in-lake variables and landscape properties on the water pCO2 variance. We found that these systems were mostly supersaturated with CO2 (92% spatially and 72% seasonally) regardless of their trophic status and landscape properties. The pCO2 values (9-40,020 µatm) were within the range found in tropical ecosystems, and higher (p < 0.005) than pCO2 values recorded from high-latitude ecosystems. Water volume had a negative effect on the trophic state (r = -0.63), which mediated a positive indirect effect on pCO2 (r = 0.4), representing an important negative feedback in the context of climate change-driven reduction in precipitation. Our results demonstrated that precipitation drives the pCO2 seasonal variability, with significantly higher pCO2 during the rainy season (F = 16.67; p < 0.001), due to two potential main mechanisms: (1) phytoplankton dilution and (2) increasing inputs of terrestrial CO2 from the catchment. We conclude that at low latitudes, precipitation is a major climatic driver of pCO2 variability by influencing volume variations and linking lentic ecosystems to their catchments.