Biodiversity loss is occurring globally at unprecedented rates, altering the functioning of the Earth’s ecosystems. Multiple processes are often key components of ecosystem functioning, but it is ...unclear how biodiversity loss affects ecosystem multifunctionality (i.e., the ability of ecosystems to maintain multiple processes simultaneously). This is particularly true for some ecosystem types such as streams, which have been understudied, despite their key role in global biogeochemical cycles and their serious impairment by the widespread loss of riparian vegetation as a result of global change. Using a microcosm experiment, we tested whether losing riparian plant diversity affected stream multifunctionality, taking into account nine key processes related to litter decomposition, animal biomass production, and nutrient cycling, and simulating plant species loss from four to one in the presence or absence of litter-feeding detritivores. Multifunctionality increased with plant diversity in the presence of detritivores and decreased in their absence, evidencing a key role of detritivores in biodiversity–ecosystem-functioning (BEF) relationships. Moreover, by exploring effects of plant diversity on each process individually we were able to reveal potential mechanisms underlying BEF relationships; for example, effects of plant diversity on nutrient cycling occurred at least partly via indirect nutrient transfer, and were possibly accompanied by changes in microbial stoichiometry. Such mechanisms were unnoticeable when examining multifunctionality metrics, suggesting that individual processes provide crucial information to understand how stream ecosystem functioning is impaired by biodiversity loss.
Streams draining forested landscapes are fuelled by terrestrial plant litter, which can be transported downstream or retained and broken down locally. However, fluxes of plant litter in streams can ...vary at multiple spatio‐temporal scales, affecting the availability of this key resource in heterotrophic stream food webs.
To explore this question we quantified several processes related to litter dynamics (i.e. litter inputs, storage, losses by transport and losses by breakdown) by sampling litter at multiple sites in three streams of the Brazilian Cerrado biome (which has a tropical wet–dry climate) for 2 years. We assessed the relative contribution of different spatial (among and within streams) and temporal scales (annual, seasonal and monthly) to total variability of these processes (hereafter fluxes).
Spatial and temporal variability of fluxes were both high, but spatial variation was 1.67‐fold greater than temporal variation (61 versus 37%, respectively), especially at the within‐stream scale (50% overall); an exception was litterfall, which varied less spatially than temporally (24 versus 76%). Temporal variation of litter storage (and hence availability to consumers) was mostly seasonal and due to differences in net transport.
Inputs and transport were higher in the wet than the dry season (wet versus dry season, 1.45 versus 0.92 and 1.43 versus 0.06 g litter m−2 day−1), while breakdown was similar between both seasons (0.88 versus 0.94 g litter m−2 day−1). Storage (i.e. accumulation) rate was positive and negative in the dry and wet season, respectively, indicating that litter was stored in the dry season and exported in the wet season. The transitional dry–wet season showed the highest inputs, breakdown and storage (3.21, 1.63 g litter m−2 day−1 and 145 g litter m−2), while the wet–dry season showed lower inputs (as in the dry season), higher transport (as in the wet season) and lower breakdown and storage than the other seasons (0.93, 0.65, 0.31 g litter m−2 day−1 and 24 g litter m−2).
Our results underscore the role of variation in biophysical drivers of litter fluxes within streams (e.g. pool–riffle configuration, substrate features, biological communities), and suggest that high within‐stream replication is necessary to study litter fluxes at larger scales and over time. The seasonal patterns suggested potential changes in litter dynamics under future climate scenarios in the tropics, including increased storage due to reduced transport in a drier climate.
In Chile, mediterranean climate conditions only occur in the Central Zone (ChMZ). Despite its small area, this mediterranean climate region (med-region) has been recognised as a hotspot for ...biodiversity. However, in contrast to the rivers of other med-regions, the rivers in the ChMZ have been studied infrequently, and knowledge of their freshwater biodiversity is scarce and fragmented. We gathered information on the freshwater biodiversity of ChMZ, and present a review of the current knowledge of the principal floral and faunal groups. Existing knowledge indicates that the ChMZ has high levels of endemism, with many primitive species being of Gondwanan origin. Although detailed information is available on most floral groups, most faunal groups remain poorly known. In addition, numerous rivers in the ChMZ remain completely unexplored. Taxonomic specialists are scarce, and the information available on freshwater biodiversity has resulted from studies with objectives that did not directly address biodiversity issues. Research funding in this med-region has a strong applied character and is not focused on the knowledge of natural systems and their biodiversity. Species conservation policies are urgently required in this highly diverse med-region, which is also the most severely impacted and most populated region of the country.
Introduction of alien fish is a major problem for the conservation of amphibians inhabiting originally fishless mountain streams. While fish eradication programs in lakes and ponds have proven ...successful for the recovery of amphibian populations, there is no such information for stream-dwelling amphibians, possibly because fish removal from streams is difficult and costly. Here, we show the first case of successful recovery of a stream-dwelling amphibian (Rana iberica) in a mountain area of central Spain, following eradication of introduced brook trout (Salvelinus fontinalis) and native brown trout (Salmo trutta) translocated from downstream reaches by local anglers. Electrofishing for 12 consecutive years eradicated both fish species in the introduced area, and allowed the recovery of the R. iberica population as a result of natural recolonization from nearby streams and reintroduction of captive-reared individuals. Our results demonstrate how electrofishing can be a costly but effective method for the eradication of introduced fish and the conservation of stream-dwelling amphibians.
Tropical forests are declining at unprecedented rates in favour of agriculture, and streams can be severely impacted due to effects of multiple stressors that have rarely been considered together in ...tropical studies. We studied the effects of multiple stressors associated with agricultural practices (pesticide toxicity, nutrient enrichment and habitat alteration-quantified as TUmax, soluble reactive phosphorus concentration and sedimentation, respectively) on macroinvertebrate communities in a tropical catchment in Panama (13 stream sites sampled in 20 occasions from 2015 to 2017, with 260 samples in total). We examined how macroinvertebrate abundance, taxonomic richness, community composition and biotic indices (SPEAR and BMWP/PAN, which were specifically designed to detect pesticide toxicity and nutrient enrichment, respectively) varied depending on the studied stressors, considering their single and combined effects. Our analyses revealed significant effects of the studied stressors on macroinvertebrate communities, with two particular results that merit further attention: (1) the fact that pesticide toxicity affected BMWP/PAN, but not SPEAR, possibly because the former had been adapted for local fauna; and (2) that most stressors showed antagonistic interactions (i.e., lower combined effects than expected from their individual effects). These results highlight the need for toxicity bioassays with tropical species that allow adaptations of biotic indices, and of observational and manipulative studies exploring the combined effects of multiple stressors on tropical macroinvertebrate communities and ecosystems, in order to predict and manage future anthropogenic impacts on tropical streams.
•Extreme climatic events (ECEs) affected litter decomposition in stream microcosms.•Heating enhanced short-term nutrient leaching and long-term microbial biomass accrual.•Freezing tended to enhance ...decomposition but had inconsistent effects.•Both ECEs strongly and consistently reduced detritivore growth.•Consumer physiological variables can be good indicators of environmental change.
Extreme temperature events have increased in intensity, duration and frequency in the last century, with potential consequences on organisms and ecosystems. In many streams, leaf litter of terrestrial origin is a key resource for microorganisms and some detritivores, and its decomposition has a main role on ecosystem functioning and is often used as an indicator of ecological integrity. As litter is often exposed to atmospheric conditions before entering the stream, extreme warming and freezing events may alter its physicochemical structure and affect decomposition and associated detritivores. We tested this prediction in a microcosm experiment by exposing litter of three tree species (in single-species treatments and the 3-species mixture) to different temperature pre-treatments: heating (40 °C), freezing (−20 °C) and both (heating followed by freezing). We then examined changes in litter traits due to leaching (72 h), litter decomposition in the absence and presence of detritivores, and detritivore growth (28 d), with focus on mass and nutrient (nitrogen and phosphorus) changes. Nutrient leaching was promoted mostly by the heating pre-treatment, which apparently produced lower-quality litter. However, microbial activity mostly resulted in litter mass and nutrient gain, which were reinforced by the heating pre-treatment, while freezing had the opposite effect. When detritivores were present, decomposition showed high variation among litter types but, again, the heating and freezing pre-treatments tended to reduce and enhance nutrient loss, respectively. The greatest and more consistent effects occurred for detritivore growth, which was reduced by temperature pre-treatments, particularly in the highest-quality litter type. In general, the sequential application of heating and freezing pre-treatments showed no synergistic effect, and the litter mixture showed similar responses to single-species treatments. Our results demonstrate that short-term extreme temperatures can modify litter quality in riparian soils and have subsequent effects on its decomposition within the stream and associated fauna, potentially altering stream food webs, ecosystem functioning and biogeochemical cycles.
Climate change and infectious disease by the chytrid fungus Batrachochytrium dendrobatidis (Bd) are major drivers of amphibian extinctions, but the potential interactions of these two factors are not ...fully understood. Temperature is known to influence (1) the infectivity, pathogenicity and virulence of Bd; (2) host-parasite dynamics, especially when both hosts and parasites are ectothermic organisms exhibiting thermal sensitivities that may or may not differ; and (3) amphibian vulnerability to extinction depending on their heat tolerance, which may decrease with infection. Thus, in a global warming scenario, with rising temperatures and more frequent and extreme weather events, amphibians infected by Bd could be expected to be more vulnerable if temperatures approach their critical thermal maximum (CTmax). However, it is also possible that predicted high temperatures could clear the Bd infection, thus enhancing amphibian survival. We tested these hypotheses by measuring CTmax values of Bd-infected and Bd-free aquatic tadpoles and terrestrial toadlets/juveniles of the common midwife toad (Alytes obstetricans) and examining whether exposure of A. obstetricans individuals to peak temperatures reaching their CTmax clears them from Bd infection. We show that (1) Bd has a wide thermal tolerance range; (2) Bd is capable of altering the thermal physiology of A. obstetricans, which is stage-dependent, lowering CTmax in tadpoles but not in toadlets; and (3) Bd infection is not cleared after exposure of tadpoles or toadlets to CTmax. Living under climatic change with rising temperatures, the effect of Bd infection might tip the balance and lead some already threatened amphibian communities towards extinction.
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•Tropical lowland stream functioning was assessed through leaf litter decomposition.•Three litter types differing in their nativeness were examined.•Microbial decomposition was ...dominant across an agricultural intervention gradient.•Detritivore-mediated decomposition reflected the intervention gradient.•Microbial decomposition indicated differences among leaf litter types.
Stream ecosystems are highly vulnerable to changes in land use and vegetation in their catchments for two reasons: firstly, they receive inputs of nutrients, contaminants and sediments through runoff; and secondly, terrestrial leaf litter is the major basal resource supporting their food webs. Leaf litter decomposition by microorganisms and detritivores is thus a key stream ecosystem process, and a valuable functional indicator of impacts associated to agriculture and other alterations of human origin. Here, we investigated the joint effects of land use changes associated to agriculture (low, medium and high intervention areas: LI, MI and HI, respectively) in a tropical lowland catchment in Panama, through a decomposition experiment using three leaf litter types differing in nativeness (Ficus insipida, native to the study area; Alnus acuminata, native to Panama but not present in the study area; and Musa balbisiana, exotic to Panama). Lowland tropical areas are often poor in litter-consuming detritivores, and we accordingly observed a high contribution of microorganisms to total decomposition (>60% on average). However, only in the presence of detritivores, decomposition of Alnus discriminated among different degrees of agricultural intervention, being higher at the LI area. Leaf litter of the native Ficus showed higher microbial decomposition than the other types, possibly in relation to a home-field advantage effect. Despite the scarcity of detritivores in tropical lowland streams compared to tropical highland or temperate streams, our study indicates that their activity reflects impacts of land use change on these streams and they should therefore be included in assessments of anthropogenic impacts.
Freshwater organisms are often sensitive to pesticides, but their sensitivity varies across different taxa and with pesticide type and action mode, as shown by multiple acute toxicity tests. Such ...variability hampers predictions about how freshwater ecosystems may be altered by pesticide toxicity, which is especially critical for understudied areas of the world such as the tropics. Furthermore, there is little information about the sensitivity of some organisms that are key components of stream food webs; this is the case of litter-feeding detritivorous invertebrates, which contribute to the fundamental process of litter decomposition. Here, we examined the sensitivity of three common detritivores Anchytarsus sp. (Coleoptera: Ptilodactylidae), Hyalella sp. (Amphipoda: Hyalellidae) and Lepidostoma sp. (Trichoptera: Lepidostomatidae) to three pesticides commonly used (the insecticides bifenthrin and chlorpyrifos and the fungicide chlorothalonil) using acute (48 or 96 h) toxicity tests. Our study demonstrates that common-use pesticides provoke the mortality of half their populations at concentrations of 0.04–2.7 μg L-1. We found that all species were sensitive to the three pesticides, with the highest sensitivity found for chlorpyrifos. Additionally, we used the approach of species sensitivity distributions (SSD) to compare our study species with Daphnia magna and other temperate and tropical invertebrates. We found that the study species were among the most sensitive species to chlorpyrifos and chlorothalonil. Our results suggest that tropical detritivores merit special attention in ecological risk assessment of pesticides and highlight the need for accurate ecotoxicological information from ecologically relevant species in the tropics.
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•We examined the sensitivity of three common detritivores to three pesticides using acute toxicity tests.•Our studied species were sensitive to the three pesticides, with the highest mortality found for chlorpyrifos.•SSD indicated that our studied species were among the most sensitive to chloropyrifos and chlorothalonil reported in the literature.•Extrapolation of ecotoxicological data with D. magna, would underestimate the real effects of pesticides in tropical stream.•We highlight the need for more ecotoxicological studies that use tropical aquatic species from different trophic levels.
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•Litterbags of a mixture of leaves, hand net, and corer was the compared techniques.•We got 540 samples in five forested wetlands temporary and permanent for one year.•Richness and ...diversity were higher with a hand net, followed by litterbags, and corer.•nMDS and ANOSIM separating two macroinvertebrate assemblages in respect to techniques.•We reinforce findings from the joint use of two techniques, hand net, and corer.
Forest wetlands are biodiversity hotspots that perform functions of vital ecological importance, but they are among the world's most threatened ecosystems. Due to their high diversity of habitats and species, the study of their benthic macroinvertebrate communities is challenging, and there is no consensus on which sampling methods allow a better representation of these communities. Here we compared the performance of 3 sampling methods (hand net, corer and litterbags) in 2 temporary and 3 permanent forested wetlands in southern Chile, which were bimonthly sampled throughout a year, with 108 samples per wetland. Our results indicated that the greatest abundance and diversity were collected with the hand net, followed by the litterbags and the corer. The composition of communities collected by the hand net and litterbags were more similar between them than that of communities collected by the corer (where Chironomidae and Oligochaeta were common). We suggest that the combined use of the hand net and corer could provide a good representation of macroinvertebrate communities in forest wetlands, as they would allow recording most of the diversity, including taxa that are both sensitive and tolerant to stressors.
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