Hydrobiologia最新文献

We experimentally tested whether the presence of a free benthic predator (Odonata naiads) alters the displacement time, the position occupied in the water column, and the proportion of food consumed by benthic and nektonic tadpoles. The presence of predators did not influence the displacement time or the proportion of food consumed by any of the two species. In the presence of predators, benthic tadpoles avoided the benthic microhabitat, increasing their time in the middle of the water column. This behavior was unexpected since the previous studies indicate that the morphology of benthic tadpoles restricts them to the bottom of water bodies. We, thus, hypothesize that such a drastic behavior change was a consequence of the real risk of predation to which the tadpoles were exposed. Our results are in accordance with the threat-sensitivity hypothesis, in which prey behave flexibly when exposed to different degrees of predation threats. Nektonic tadpoles, however, slightly increased their permanence in the water column in the presence of the same benthic predators. Therefore, we provide support for the hypothesis that predators induce greater behavioral changes in prey that exhibit patterns of microhabitat use similar to theirs.

Our objective was to assess the effects of interactions between the native Percichthys trucha and both Salmo trutta and Oncorhynchus mykiss during the juvenile period. We conducted single and multipredator (conspecific and heterospecific) functional response (FR) experiments with Meridialaris chiloeensis as native prey and estimated the functional response ratio as a predator impact metric. Our results showed that all species have type II FR, with salmonids having a greater impact on prey than native fish. In multipredator experiments, O. mykiss had a greater negative impact on P. trucha than S. trutta. The individual feeding performance of P. trucha was better under conspecific than heterospecific conditions. This study shows that the vulnerability of juvenile P. trucha to salmonid competition could be a real threat in Patagonian lotic environments.

The trophic organization of estuarine fish communities is poorly known. We used Stable Isotopes (δ¹³C and δ¹⁵N) to classify the most abundant fishes of the Atrato River Delta (Colombia) into trophic guilds. We examined trophic niches and the relationships between the abundance of the trophic guilds (catch per unit effort) and environmental variables. The zoobenthivores were the dominant trophic guild. The isotopic niche width, based on Bayesian estimate of the standard ellipse areas, was more significant for carnivores (25.3‰²) and planktivores (24.4‰²) than for omnivores (7.8‰²) and phytobenthivores (3.1‰²). The overlap combinations showed a medium probability of isotopic overlap (≈50%) between carnivores and planktivores and between carnivores and omnivores. Isotopic niche size and overlap suggested diversity in food sources and considerable niche segregation of the fish community. Mangrove area was the main factor explaining the abundance of omnivores and zoobenthivores, supporting that the causal links between mangrove habitat and local fishery production may be explained through the trophic contribution of mangroves and mangrove-related sources. The results underscore the importance of mangrove areas in the trophic organization of fish communities and can inform strategies aimed at managing the ecosystem impacts of fishing and protecting extensive mangrove areas in the southern Caribbean.

Inorganic carbon acquisition is essential to algal growth, while the limitations of dissolved inorganic carbon (DIC) on phytoplankton are still less known in lakes. Sediment is an active hot spot for microbial metabolism, driving the migration and transformation of elements in shallow lakes, which may control the DIC availability to influence algal spatiotemporal dynamics. Hence, we investigated the spatiotemporal changes of phytoplankton, DIC and sediment respiration rates in a eutrophic shallow freshwater lake under non-bloom conditions. There was a widespread deficiency of DIC in the lake, except the estuary. Sediment respiration was positively associated with changes in DIC concentrations, indicating that carbon metabolic activity of sedimentary microorganisms was an important inorganic carbon source for water columns. The availability of DIC in water columns regulated by sediment microbial respiration influenced the algal biomass, composition and productivity. The synergistic effects of seasonal temperature changes and sediment microbial respiration influenced the vertical distribution and migration of phytoplankton. Our results emphasized that carbon metabolic intensity of sediment microorganisms might play a key role in dynamics of phytoplankton, further impacting the spatiotemporal pattern and formation of algal bloom in eutrophic shallow freshwater lakes.

Appraising sexual asymmetry during maximum gonad investment (MGI) offers a sharp tool to evaluate the reproductive response of species to climate by coupling extrinsic and intrinsic factors. We comparatively analyze how the mass and physiological male and female gonad investments of the broadcast-spawning intertidal Chiton articulatus in two populations from the Mexican Tropical Pacific respond to the thermal phases of cold “La Niña” and warm “El Niño.” We found that local rather than regional temperature modulates MGI intensity and breadth in this species, evidencing higher MGI levels in the southern tropical zone (Oaxaca). Male gonad investment was higher than that of females during neutral and cold phases compared to warm thermal phases. Physiological gonad investment during MGI suggests that males spawn before females, and the adult sex ratio of each population was close to unity. Our results suggest reproductive success regulation through sexual asymmetry in both mass and physiological gonad investment, modulated by temperature changes due to thermal phases. The male bias in gonad investment found under neutral to cold temperatures suggests physiological resilience in this species, especially considering its habitat and the impact of climate change· The MGI value is a phenotypic trait that varies as a function of temperature.

Anthropic activities are expected to change species co-occurrence by altering niche availability and biotic interactions, which affects ecosystem functioning. We investigated the non-random co-occurrences of zooplankton species, which species have positive and negative co-occurrences, and which environmental factors (local and landscape) influence the species distribution and co-occurrences in Amazon lotic systems. We expected that variables related to intense changes in the landscape would influence species distribution and reduce positive and negative co-occurrences, increasing random associations. Our study was conducted in a river and twelve first- and second-order streams across three periods in the Amazon region of Brazil. We sampled zooplankton and physical and chemical variables and determined forest cover around the sampling sites. Co-occurrences were determined by probabilistic models. Total suspended solids, pH, and ammonium were the variables shaping zooplankton distribution. We observed 43 positive and six negative co-occurrences. Ammonium increased positive and negative co-occurrences and suspended solids decreased these associations. Our study provides insights into how environmental factors can alter niche availability and biotic interactions leading to different patterns of zooplankton co-occurrence in Amazon systems. This is the first study investigating such relationships in Amazon lotic systems and can help to understand risks to biodiversity and plan conservation strategies.

This work aimed to infer the time of origin and the mode of evolution of the potentially endemic ciliates of the phytotelmata, as well as delimit their dispersal routes until reaching this environment. We estimate a dated molecular phylogeny from the 18Sr-RNA sequence available from GenBank. We inferred the habitat ancestral state and the dynamics of the diversification rates related to assessed habitats. Our results showed that the arrival to phytotelmata habitats is recent and occurred numerous times and independently over evolutionary time, being the origin of potentially endemic ciliates after the appearance of bromeliads. Our data also revealed that the arrival of the ciliates to the phytotelma occurred through four distinct routes: (i) from a marine/brackish ancestor, (ii) a freshwater ancestor, (iii) a terrestrial ancestor, or (iv) a symbiotic ancestor. In addition, we noticed a significant increase in the diversification rates of potentially endemic ciliates to bromeliad phytotelma. Several ecological, morphological and evolutionary hypotheses help to explain these ciliates' evolutionary success. However, more studies with this group are needed to define complex hypotheses explaining such a process. It emphasizes the need to dedicate efforts to develop ecological and molecular studies with this group.

Forecasting the potential distribution of gastropod species with socio-environmental significance under current and future scenarios is crucial for controlling disease transmissions and biological invasions. In this study, ecological niche modeling was employed to predict the potential distribution and assess niche overlap of two problematic gastropod species in South America: the native species Biomphalaria glabrata, which serves as a vector for schistosomiasis pathogen, and the invasive Melanoides tuberculata. Our findings revealed overlapping environmental niches between native and invasive gastropod species, with the invasive species exhibiting broader environmental requirements. The distinct environmental niches of each gastropod species translate into unique potential distribution locations in geographic space, which remain largely unchanged across current and future climatic scenarios. Additionally, we provide evidence suggesting that utilizing the invasive species as a biological control for health-related species may not be advantageous without specific management strategies. Despite niche similarities, the invasive gastropod has the potential to spread to less ideal habitats for the native species. Hence, strategies to address both native and invasive mollusks should be formulated based on empirical evidence to mitigate environmental, ecological, and health concerns.

Neotropical streams stand as one of the most biodiverse aquatic ecosystems in the world. The extremely high biodiversity of these ecosystems was generated and modified by several geological events, major climatic changes, and complex ecological mechanisms. Here we synthesize ecological concepts that influence the organization of Neotropical stream biodiversity. We analyze the ecological processes from three perspectives: horizontal (i.e., competition between species), vertical (i.e., trophic organization), and regional perspectives (i.e., environmental selection, stochasticity and dispersal). Our review highlights that Neotropical streams are understudied compared to other regions considering the three ecological perspectives and the human impacts on these ecosystems. The lack of studies in the horizontal perspective is prominent compared to the other perspectives. Overall, our knowledge of the biodiversity and dynamics of Neotropical streams is concentrated on the regional perspective and especially on the anthropogenic impacts on aquatic biodiversity. We identify some gaps in knowledge and conclude that the ecology of Neotropical streams is rapidly changing in the face of the current environmental crisis generated by multiple disturbances. These results indicate an urgent need for integrated ecological studies of Neotropical streams, considering their high global proportion of biodiversity and the multiple services these ecosystems support.

Nutrient enrichment can impair the biotic integrity of steams and rivers. Nutrients derived from land use practices have been identified as sources of water quality impairment in several Central California Coast watersheds resulting in excess algal growth. We developed an algae-based multi-metric index to assess the biotic integrity of streams and rivers in this region because algae often respond directly to changes in nutrient levels. Additionally, we apply the algal index of biotic integrity to the development of an effects-based nitrogen reduction target. Eleven individual metrics based on diatom autecologies, community structure, ecological guilds, tolerance, and intolerance were incorporated into the index. All algal production metrics failed reproducibility criteria for inclusion in the index. The index of biotic integrity was highly correlated with human disturbance (r = − 0.6213) and was significantly different between classes of least-, intermediate-, and most-disturbed sites. Piecewise linear regression showed a steep negative relationship between nitrate–N and the index with a breakpoint of 0.505 mg/L nitrate–N, above which the negative trend became insignificant. This change in the relationship between nitrate and the index of biotic integrity suggests that this breakpoint can aid the development of a reasonable effects-based criterion for nitrate–N in this region.