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All animals carry specialized microbiomes, and their gut microbiota are continuously released into the environment through excretion of waste. Here we propose the meta-gut as a novel conceptual framework that addresses the ability of the gut microbiome released from an animal to function outside the host and alter biogeochemical processes mediated by microbes. We demonstrate this dynamic in the hippopotamus (hippo) and the pools they inhabit. We used natural field gradients and experimental approaches to examine fecal and pool water microbial communities and aquatic biogeochemistry across a range of hippo inputs. Sequencing using 16S RNA methods revealed community coalescence between hippo gut microbiomes and the active microbial communities in hippo pools that received high inputs of hippo feces. The shared microbiome between the hippo gut and the waters into which they excrete constitutes a meta-gut system that could influence the biogeochemistry of recipient ecosystems and provide a reservoir of gut microbiomes that could influence other hosts. We propose that meta-gut dynamics may also occur where other animal species congregate in high densities, particularly in aquatic environments.

Hippopotami (hippos) are ecosystem engineers that subsidize aquatic ecosystems through the transfer of organic matter and nutrients from their terrestrial grazing, with potentially profound effects on aquatic biogeochemistry. We examined the influence of hippo subsidies on biogeochemical cycling in pools of varying hydrology and intensity of hippo use in the Mara River of Kenya. We sampled upstream, downstream, and at the surface and bottom of pools of varying volume, discharge, and hippo numbers, both before and after flushing flows. The product of hippo number and water residence time served as an index of the influence of hippo subsidies (hippo subsidy index, HSI) on aquatic biogeochemistry. Low-HSI hippo pools remained oxic between flushing flows and could be a source or sink for nutrients. High-HSI hippo pools quickly became anoxic between flushing flows and exported nutrients and byproducts of anaerobic microbial metabolism, including high concentrations of total ammonia nitrogen, hydrogen sulfide, and methane. Medium-HSI hippo pools were more similar to high-HSI hippo pools but with lower concentrations of reduced substances. Episodic high discharge events flushed pools and reset them to the oxic state. Transitions from oxic to anoxic states depended on water residence time, with faster transitions to anoxia in pools experiencing smaller flushing flows. Frequent shifts between these alternative oxic and anoxic states create heterogeneity in space and time in pools as well as in downstream receiving waters. In river systems where the influence of hippos on water quality is a concern, maintaining the natural flow regime, including flushing flows, ameliorates impacts of hippos.

Top predators have substantial downstream effects on the structure, function, and resilience of ecosystems. The influence of top predators on an ecosystem can vary if they occur within multiple habitat types and have a wide niche breadth due to spatiotemporal changes in diet. We examined spatial patterns in trophic position and niche width for an economically important reef-associated fishery species, the giant trevally Caranx ignobilis. We sampled 4 localities in the western Indian Ocean representing different habitats: coral atolls, coastal reefs, and granitic islands. We analyzed isotopic ratios of carbon (13C/12C) and nitrogen (15N/14N), and performed compound-specific amino acid stable isotope analysis (AA-CSIA) to control for baseline nitrogen variation. Our analysis of 12 juveniles and 43 adults revealed wide variation in trophic niche breadth between sampling sites and an offshore to coastal gradient in carbon that drove niche distinctiveness between localities. We observed niche width patterns suggestive of ontogenetic changes in diet and habitat utilization and larger niche sizes at the oceanic island sites than the coastal site. Trophic position estimates ranged from 3.5-5, expanding the trophic range of C. ignobilis relative to previous studies using AA-CSIA and placing it at the equivalent trophic level as many predatory sharks. Our study corroborates prior evidence that C. ignobilis is an important apex predator in reef and island ecosystems. Additionally, we show how evaluating spatiotemporal components of trophic ecology of marine predators is critical for characterizing their functional role and ecosystem influence, allowing for targeted conservation efforts.

Introduced species can have strong ecological, social and economic effects on their non-native environment. Introductions of megafaunal species are rare and may contribute to rewilding efforts, but they may also have pronounced socio-ecological effects because of their scale of influence. A recent introduction of the hippopotamusHippopotamus amphibiusinto Colombia is a novel introduction of a megaherbivore onto a new continent, and raises questions about the future dynamics of the socio-ecological system into which it has been introduced. Here we synthesize current knowledge about the Colombian hippopotamus population, review the literature on the species to predict potential ecological and socio-economic effects of this introduction, and make recommendations for future study. Hippopotamuses can have high population growth rates (7–11%) and, on the current trajectory, we predict there could be 400–800 individuals in Colombia by 2050. The hippopotamus is an ecosystem engineer that can have profound effects on terrestrial and aquatic environments and could therefore affect the native biodiversity of the Magdalena River basin. Hippopotamuses are also aggressive and may pose a threat to the many inhabitants of the region who rely upon the Magdalena River for their livelihoods, although the species could provide economic benefits through tourism. Further research is needed to quantify the current and future size and distribution of this hippopotamus population and to predict the likely ecological, social and economic effects. This knowledge must be balanced with consideration of social and cultural concerns to develop appropriate management strategies for this novel introduction.

Secondary contact may have important implications for ecological and evolutionary processes; however, few studies have tracked the outcomes of secondary contact from its onset in natural ecosystems. We evaluated an anadromous alewife (Alosa pseudoharengus ) reintroduction project in Rogers Lake (Connecticut, USA), which contains a landlocked alewife population that was isolated as a result of colonial‐era damming. After access to the ocean was restored, adult anadromous alewife were stocked into the lake. We assessed anadromous juvenile production, the magnitude and direction of introgression, and the potential for competition between ecotypes. We obtained fin clips from all adult alewife stocked into the lake during the restoration and a sample of juveniles produced in the lake two years after the stocking began. We assessed the ancestry of juveniles using categorical assignment and pedigree reconstruction with newly developed microhaplotype genetic markers. Anadromous alewives successfully spawned in the lake and hybridized with the landlocked population. Parentage assignments revealed that male and female anadromous fish contributed equally to juvenile F1 hybrids. The presence of landlocked backcrosses shows that some hybrids were produced within the first two years of secondary contact, matured in the lake, and reproduced. Therefore, introgression appears directional, from anadromous into landlocked, in the lake environment. Differences in estimated abundance of juveniles of different ecotypes in different habitats were also detected, which may reduce competition between ecotypes as the restoration continues. Our results illustrate the utility of restoration projects to study the outcomes of secondary contact in real ecosystems.

The Mara River basin is a trans-boundary basin of international importance. It forms the headwaters of the Nile River and serves as the primary dry season water source for an estimated 1.1 million rural people and the largest remaining overland migration of 1.4 million wildebeest in the Serengeti-Mara Ecosystem. Changes throughout the basin are impacting the quantity and quality of the Mara River, yet the historical context of environmental conditions in the basin is not well known. We collected sediment cores throughout the wetland at the mouth of the Mara River, and we used isotopic dating methods and a suite of analyses to examine historical patterns of sediment quantity and source, mercury contamination, and carbon and nutrient loading. Our results show that ecological conditions in the Mara River basin were fairly stable over paleoecological time scales (2000–1000 years before present), but there has been a period of rapid change in the basin over the last 250 years, particularly since the 1960s. A shift in the source and quantity of sediments in the river began in the late 1700s and became much more pronounced in the 1950s and 1960s, coincident with increasing mercury concentrations. The quantity of sediment from the Upper Mara increased, particularly since 1960, but the proportion of total sediment from this region decreased as the Talek and Middle Mara portions of the basin began producing more sediment. The decadal oscillation in sediment accumulation was congruent with known periods of extreme precipitation events. Carbon and nitrogen loading also increased since the 1960s, and the shift in the isotopic ratio of nitrogen provides evidence for increased anthropogenic loading. Altogether, these data likely reflect patterns of change also experienced in other basins throughout East Africa.

Variation in eye size is ubiquitous across taxa. Increased eye size is correlated with improved vision and increased fitness via shifts in behavior. Tests of the drivers of eye size evolution have focused on macroevolutionary studies evaluating the importance of light availability. Predator-induced mortality has recently been identified as a potential driver of eye size variation. Here, we tested the influence of increased predation by the fish predator, the alewife (Alosa pseudoharengus) on eye size evolution in waterfleas (Daphnia ambigua) from lakes in Connecticut. We quantified the relative eye size of Daphnia from lakes with and without alewife using wild-caught and third-generation laboratory reared specimens. This includes comparisons between lakes where alewife are present seasonally (anadromous) or permanently (landlocked). Wild-caught specimens did not differ in eye size across all lakes. However, third-generation lab reared Daphnia from lakes with alewife, irrespective of the form of alewife predation, exhibited significantly larger eyes than Daphnia from lakes without alewife. This genetically based increase in eye size may enhance the ability of Daphnia to detect predators. Alternatively, such shifts in eye size may be an indirect response to Daphnia aggregating at the bottom of lakes. To test these mechanisms, we collected Daphnia as a function of depth and found that eye size differed in Daphnia found at the surface versus the bottom of the water column between anadromous alewife and no alewife lakes. However, we found no evidence of Daphnia aggregating at the bottom of lakes. Such results indicate that the evolution of a larger eye may be explained by a connection between eyes and enhanced survival. We discuss the cause of the lack of concordance in eye size variation between our phenotypic and genetic specimens and the ultimate drivers of eye size.

Animal carcasses can provide important resources for a suite of consumers, and bones may provide a largely overlooked component of this resource, as they contain a large proportion of the phosphorus (P) in a carcass and they can persist for decades to millennia. We synthesized several datasets from our research in the Mara River, in which annual mass drownings of wildebeest (Connochaetes taurinus) contribute 2.2 × 105 kg of bones per year, to examine the ecological role that bone could play in this river ecosystem and to prioritize research questions on the role of bones in aquatic ecosystems in general. We measured bone stoichiometry and used in-stream litterbags to measure bone decomposition rate, both of which varied by bone type. Decomposition occurs as a two-stage process, with 15% of the mass being relatively labile and decomposing in 80–120 days and the remaining recalcitrant portion decomposing over > 80 years, leading to an estimated standing stock of 5.1 × 106 kg bones in the river. We used mesocosm experiments to measure leaching rates from bones. Leachate from fresh bones was an order of magnitude higher in inorganic nitrogen (N) than P; however, aged bones from the river leached much more P than N, which stimulated primary production. Biofilms growing on bones had five times greater chlorophyll a and two times greater organic matter than those growing on rocks, although algal composition was not significantly different between the two substrates. Biofilms growing on bones also differed from biofilms on rocks in carbon (C) and N stable isotope signature. Mixing models suggest that biofilms on bones account for 19% of macroinvertebrate and 24% of fish tissues in the Mara River, even months after carcasses were present. In combination, these findings suggest that bones may influence nutrient cycling, ecosystem function, and food webs in the Mara River, potentially on decadal time scales. Bones may also be important in other aquatic ecosystems, and mass extirpations of large land mammals may have led to a loss of this resource. Large animal bones may play a unique role in ecosystems via their slow release of limiting nutrients.

Animals can be important vectors for the movement of resources across ecosystem boundaries. Animals add resources to ecosystems primarily through egestion, excretion, and carcasses, and the stoichiometry and bioavailability of these inputs likely interact with characteristics of the recipient ecosystem to determine their effects on ecosystem function. We studied the influence of hippopotamus excretion/egestion and wildebeest carcasses, and their interactions with discharge, in the Mara River, Kenya. We measured nutrient dissolution and decomposition rates of wildlife inputs, the influence of inputs on nutrient concentrations and nutrient limitation in the river and the influence of inputs on biofilm growth and function in both experimental streams and along a gradient of inputs in the river. We found that hippopotamus excretion/egestion increases ammonium and coarse particulate organic matter in the river, and wildebeest carcasses increase ammonium, soluble reactive phosphorus, and total phosphorus. Concentrations of dissolved carbon and nutrients in the water column increased along a gradient of wildlife inputs and during low discharge, although concentrations of particulate carbon decreased during low discharge due to deposition on the river bottom. Autotrophs were nitrogen limited and heterotrophs were carbon limited and nitrogen and phosphorus colimited upstream of animal inputs but there was no nutrient limitation downstream of inputs. In experimental streams, hippo and wildebeest inputs together increased biofilm gross primary production (GPP) and respiration (R). These results differed in the river, where low concentrations of hippo inputs increased gross primary production (GPP) and respiration (R) of biofilms, but high concentrations of hippo inputs in conjunction with wildebeest inputs decreased GPP. Our research shows that inputs from large wildlife alleviate nutrient limitation and stimulate ecosystem metabolism in the Mara River and that the extent to which these inputs subsidize the ecosystem is mediated by the quantity and quality of inputs and discharge of the river ecosystem. Thus, animal inputs provide an important ecological subsidy to this river, and animal inputs were likely important in many other rivers prior to the widespread extirpation of large wildlife.

The recent increase in river restoration projects is altering habitat connectivity for many aquatic species, increasing the chance that previously isolated populations will come into secondary contact. Anadromous and landlocked alewife (Alosa pseudoharengus) are currently undergoing secondary contact as a result of a fishway installation at Rogers Lake in Old Lyme, Connecticut. To determine the degree of prezygotic isolation and potential for hybridization between alewife life history forms, we constructed spawning time distributions for two anadromous and three landlocked alewife populations using otolith‐derived age estimates. In addition, we analyzed long‐term data from anadromous alewife migratory spawning runs to look for trends in arrival date and spawning time. Our results indicated that anadromous alewife spawned earlier and over a shorter duration than landlocked alewife, but 3%–13% of landlocked alewife spawning overlapped with the anadromous alewife spawning period. The degree of spawning time overlap was primarily driven by annual and population‐level variation in the timing of spawning by landlocked alewife, whereas the timing and duration of spawning for anadromous alewife were found to be relatively invariant among years in our study system. For alewife and many other anadromous fish species, the increase in fish passage river restoration projects in the coming decades will re‐establish habitat connectivity and may bring isolated populations into contact. Hybridization between life history forms may occur when prezygotic isolating mechanisms are minimal, leading to potentially rapid ecological and evolutionary changes in restored habitats.

The value of biodiversity is widely appreciated, but we are only beginning to understand the interplay of processes that generate biodiversity and their consequences for coevolutionary interactions. Whereas predator–prey coevolution is most often analyzed in the context of evolutionary arms races, much less has been written about how predators are affected by, and respond to, evolutionary diversification in their prey. We hypothesize here that adaptive radiation of prey may lead to diversification and potentially speciation in predators, a process that we call an upwards adaptive radiation cascade. In this paper we lay out the conceptual basis for upwards adaptive radiation cascades, explore evidence for such cascades, and finally advocate for intensified research.

Consumers with different seasonal life histories encounter different communities of producers during specific seasonal phases. If consumers evolve to prefer the producers that they encounter, then consumers may reciprocally influence the temporal composition of producer communities. Here, we study the keystone consumer Daphnia ambigua, whose seasonal life history has diverged due to intraspecific predator divergence across lakes of New England. We ask whether grazing preferences of Daphnia have diverged also and test whether any grazing differences influence temporal composition patterns of producers. We reared clonal populations of Daphnia from natural populations representing the two diverged life history types for multiple generations. We conducted short‐term (24 hr) and long‐term (27 days) grazing experiments in equal polycultures consisting of three diatom and two green algae species, treated with no consumer, Daphnia from lakes with anadromous alewife, or from lakes with landlocked alewife. After 24 hr, life history and grazing preference divergence in Daphnia ambigua drove significant differences in producer composition. However, those differences disappeared at the end of the 27‐day experiment. Our results illustrate that, despite potentially more complex long‐term dynamics, a multitrophic cascade of evolutionary divergence from a predator can influence temporal community dynamics at the producer level.

Animals can impact freshwater ecosystem structure and function in ways that persist well beyond the animal’s active presence. These legacy effects can last for months, even decades, and often increase spatial and temporal heterogeneity within a system. Herein, we review examples of structural, biogeochemical, and trophic legacies from animals in stream and river ecosystems with a focus on large vertebrates. We examine how the decline or disappearance of many native animal populations has led to the loss of their legacy effects. We also demonstrate how anthropogenically altered animal populations, such as livestock and invasive species, provide new legacy effects that may partially replace lost animal legacies. However, these new effects often have important functional differences, including stronger, more widespread and homogenizing effects. Understanding the influence of animal legacy effects is particularly important as native animal populations continue to decline and disappear from many ecosystems, because they illustrate the long-term and often unanticipated consequences of biodiversity loss. We encourage the conservation and restoration of native species to ensure that both animal populations and their legacy effects continue to support the structure and function of river ecosystems.

The annual migration of ∼1.2 million wildebeest (Connochaetes taurinus) through the Serengeti Mara Ecosystem is the largest remaining overland migration in the world. One of the most iconic portions of their migration is crossing of the Mara River, during which thousands drown annually. These mass drownings have been noted, but their frequency, size, and impact on aquatic ecosystems have not been quantified. Here, we estimate the frequency and size of mass drownings in the Mara River and model the fate of carcass nutrients through the river ecosystem. Mass drownings (>100 individuals) occurred in at least 13 of the past 15 y; on average, 6,250 carcasses and 1,100 tons of biomass enter the river each year. Half of a wildebeest carcass dry mass is bone, which takes 7 y to decompose, thus acting as a long-term source of nutrients to the Mara River. Carcass soft tissue decomposes in 2-10 wk, and these nutrients are mineralized by consumers, assimilated by biofilms, transported downstream, or moved back into the terrestrial ecosystem by scavengers. These inputs comprise 34-50% of the assimilated diet of fish when carcasses are present and 7-24% via biofilm on bones after soft tissue decomposition. Our results show a terrestrial animal migration can have large impacts on a river ecosystem, which may influence nutrient cycling and river food webs at decadal time scales. Similar mass drownings may have played an important role in rivers throughout the world when large migratory herds were more common features of the landscape.

Incluye contenido parcial de los autores Biological invasion is one of the main threats to native biodiversity. For a speciesto become invasive, it must be voluntarily or involuntarily introduced by humans into a nonna-tive habitat. Mammals were among first taxa to be introduced worldwide for game, meat, and labor, yet the number of species introduced in the Neotropics remains unknown. In this dataset, we make available occurrence and abundance data on mammal species that (1) transposeda geographical barrier and (2) were voluntarily or involuntarily introduced by humans into theNeotropics. Our data set is composed of 73,738 historical and current georeferenced recordson alien mammal species of which around 96% correspond to occurrence data on 77 speciesbelonging to eight orders and 26 families. Data cover 26 continental countries in the Neotrop-ics, ranging from Mexico and its frontier regions (southern Florida and coastal-central Floridain the southeast United States) to Argentina, Paraguay, Chile, and Uruguay, and the 13 coun-tries of Caribbean islands. Our data set also includes neotropical species (e.g.,Callithrixsp.,Myocastor coypus,Nasua nasua)considered alien in particular areas of Neotropics. The mostnumerous species in terms of records are fromBossp. (n=37,782),Sus scrofa(n=6,730), andCanis familiaris(n=10,084); 17 species were represented by only one record (e.g., Syncerus caf-fer, Cervus timorensis, Cervus unicolor, Canis latrans). Primates have the highest number of spe-cies in the data set (n=20 species), partly because of uncertainties regarding taxonomicidentification of the generaCallithrix,which includes the speciesCallithrix aurita, Callithrixflaviceps, Callithrix geoffroyi, Callithrix jacchus, Callithrix kuhlii, Callithrix penicillata, andtheir hybrids. This unique data set will be a valuable source of information on invasion riskassessments, biodiversity redistribution and conservation-related research. There are no copy-right restrictions. Please cite this data paper when using the data in publications. We alsorequest that researchers and teachers inform us on how they are using the data

Grazing hippos are key species in transfer of silicon from terrestrial grasses to lake diatoms., While the importance of grasslands in terrestrial silicon (Si) cycling and fluxes to rivers is established, the influence of large grazers has not been considered. Here, we show that hippopotamuses are key actors in the savannah biogeochemical Si cycle. Through a detailed analysis of Si concentrations and stable isotope compositions in multiple ecosystem compartments of a savannah-river continuum, we constrain the processes influencing the Si flux. Hippos transport 0.4 metric tons of Si day−1 by foraging grass on land and directly egesting in the water. As such, they bypass complex retention processes in secondary soil Si pools. By balancing internal processes of dissolution and precipitation in the river sediment, we calculate that hippos affect up to 76% of the total Si flux. This can have a large impact on downstream lake ecosystems, where Si availability directly affects primary production in the diatom-dominated phytoplankton communities.

Bycatch of mid-trophic-level anadromous fishes that connect marine and freshwater ecosystems is a growing conservation concern. Anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) are important components of coastal freshwater and marine food webs, but have experienced dramatic declines in the abundances of spawning adults. Freshwater-focused restoration efforts have yielded few consistent signs of recovery, raising concerns that bycatch in Northwest Atlantic commercial fisheries may be negating these conservation actions. Using data from 15 microsatellites genotyped for baseline populations and bycatch, we conducted genetic stock identification to understand how bycatch was partitioned among previously identified regional genetic stocks. We then combined this information with fishery observer data to estimate genetic stock-specific bycatch mortality for the southern New England Atlantic herring fishery (2012–2013). Bycatch overall, but especially in the Atlantic herring fishery, was disproportionately assigned to the most severely depleted genetic stocks (alewife southern New England stock — 70% of assignments; blueback herring mid-Atlantic stock — 78% of assignments). These genetic stocks overlap in the region surrounding Long Island Sound, suggesting that bycatch taken from this area in recent years may be negatively impacting recovery efforts in this region. Our study suggests that mitigating bycatch on the southern New England fishing grounds may benefit recovery efforts for alewife and blueback herring genetic stocks that have experienced the greatest declines in spawning adult abundances.

Competitive diversification, that is, when increasing intraspecific competition promotes population niche expansion, is commonly invoked in evolutionary studies and currently plays a central role in how we conceptualize the process of adaptive diversification. Despite the frequency with which this idea is cited, the empirical evidence for the process is somewhat limited, and the findings of these studies have yet to be weighed objectively through synthesis. Here, we sought to fill this gap by reviewing the existing literature and collecting the data necessary to assess the evidence for competition as a diversifying force. Additionally, we sought to test a more recent hypothesis, which suggests that competition can act to both promote and inhibit dietary diversification depending on the degree to which a consumer depletes its resources. The surprising result of this synthesis was that increasing competition did not have a mean positive effect on population‐level diet breadth or the degree of individual specialization. Instead, we found that increasing intraspecific competition had a restricting effect on population‐level diet breadth in as many cases as it had a diversifying effect. This wide disparity in the effect of competition on consumer diet variation was negatively related to a metric for consumer resource depletion. Altogether, these findings call into question a long‐standing assumption of basic evolutionary models and lend some support to recent theoretical predictions. Specifically, these findings support the idea that competition is primarily diversifying for species with a small effect (per unit biomass) on their resources and that resource depletion limits the diversifying effect of competition for consumers with larger ecological effects.

In many regions of the world, populations of large wildlife have been displaced by livestock, and this may change the functioning of aquatic ecosystems owing to significant differences in the quantity and quality of their dung. We developed a model for estimating loading rates of organic matter (dung) by cattle for comparison with estimated rates for hippopotamus in the Mara River, Kenya. We then conducted a replicated mesocosm experiment to measure ecosystem effects of nutrient and carbon inputs associated with dung from livestock (cattle) versus large wildlife (hippopotamus). Our loading model shows that per capita dung input by cattle is lower than for hippos, but total dung inputs by cattle constitute a significant portion of loading from large herbivores owing to the large numbers of cattle on the landscape. Cattle dung transfers higher amounts of limiting nutrients, major ions and dissolved organic carbon to aquatic ecosystems relative to hippo dung, and gross primary production and microbial biomass were higher in cattle dung treatments than in hippo dung treatments. Our results demonstrate that different forms of animal dung may influence aquatic ecosystems in fundamentally different ways when introduced into aquatic ecosystems as a terrestrially derived resource subsidy.

Understanding the factors that affect water quality and the ecological services provided by freshwater ecosystems is an urgent global environmental issue. Predicting how water quality will respond to global changes not only requires water quality data, but also information about the ecological context of individual water bodies across broad spatial extents. Because lake water quality is usually sampled in limited geographic regions, often for limited time periods, assessing the environmental controls of water quality requires compilation of many data sets across broad regions and across time into an integrated database. LAGOS-NE accomplishes this goal for lakes in the northeastern-most 17 US states. LAGOS-NE contains data for 51 101 lakes and reservoirs larger than 4 ha in 17 lake-rich US states. The database includes 3 data modules for: lake location and physical characteristics for all lakes; ecological context (i.e., the land use, geologic, climatic, and hydrologic setting of lakes) for all lakes; and in situ measurements of lake water quality for a subset of the lakes from the past 3 decades for approximately 2600–12 000 lakes depending on the variable. The database contains approximately 150 000 measures of total phosphorus, 200 000 measures of chlorophyll, and 900 000 measures of Secchi depth. The water quality data were compiled from 87 lake water quality data sets from federal, state, tribal, and non-profit agencies, university researchers, and citizen scientists. This database is one of the largest and most comprehensive databases of its type because it includes both in situ measurements and ecological context data. Because ecological context can be used to study a variety of other questions about lakes, streams, and wetlands, this database can also be used as the foundation for other studies of freshwaters at broad spatial and ecological scales.

From agriculture to public health to civil engineering, managing antimicrobial resistance presents a considerable challenge. The dynamics underlying resistance evolution reflect inherently spatial processes. Resistant pathogen strains increase in frequency when a strain that emerges in one locale can spread and replace pathogen subpopulations formerly sensitive to the antimicrobial agent. Moreover, the strength of selection for antimicrobial resistance is in part governed by the extent of antimicrobial use. Thus, altering how antimicrobials are used across a landscape can potentially shift the spatial context governing the dynamics of antimicrobial resistance and provide a potent management tool. Here, we model how the efficacy of adjusting antimicrobial use over space to manage antimicrobial resistance is mediated by competition among pathogen strains and the topology of pathogen metapopulations. For several pathogen migration scenarios, we derive critical thresholds for the spatial extent of antimicrobial use below which resistance cannot emerge, and relate these thresholds to (a) the ability to eradicate antimicrobial‐sensitive pathogens locally and (b) the strength of the trade‐off between resistance ability and competitive performance where antimicrobial use is absent. We find that in metapopulations where patches differ in connectedness, constraining antimicrobial use across space to mitigate resistance evolution only works if the migration of the resistant pathogen is modest; yet, this situation is reversed if the resistant strain has a high colonization rate, with variably connected metapopulations exhibiting less sensitivity to reducing antimicrobial use across space. Furthermore, when pathogens are alternately exposed to sites with and without the antimicrobial, bottlenecking resistant strains through sites without an antimicrobial is only likely to be effective under a strong competition–resistance trade‐off. We therefore identify life‐history constraints that are likely to suggest which pathogens can most effectively be controlled by a spatially targeted antimicrobial regime. We discuss implications of our results for managing and thinking about antimicrobial resistance evolution in spatially heterogeneous contexts.

Stability contributes to the persistence of ecological communities, yet the interactions among different stabilizing forces are poorly understood. We assembled mesocosms with an algal resource and one to eight different clones of the consumer Daphnia ambigua and tracked algal and Daphnia abundances through time. We then fitted coupled ordinary differential equations (ODEs) to the consumer-resource time series. We show that variation in different components of stability (local stability and the magnitude of population fluctuations) across mesocosms arises through variation in life history traits and the functional processes represented by ODE model parameters. Local stability was enhanced by increased algal growth rate and Daphnia mortality and foraging rate. Population fluctuations were dampened by high Daphnia conversion efficiency and lower interaction strengths, low algal growth rate, high Daphnia death rate, and low Daphnia foraging. These results indicate that (1) stability in consumer-resource systems may arise through the net effect of multiple related stabilizing pathways and (2) different aspects of stability can vary independently and may respond in opposite directions to the same forces.

Human activity is causing wild populations to experience rapid trait change and local extirpation. The resulting effects on intraspecific variation could have substantial consequences for ecological processes and ecosystem services. Although researchers have long acknowledged that variation among species influences the surrounding environment, only recently has evidence accumulated for the ecological importance of variation within species. We conducted a meta-analysis comparing the ecological effects of variation within a species (intraspecific effects) with the effects of replacement or removal of that species (species effects). We evaluated direct and indirect ecological responses, including changes in abundance (or biomass), rates of ecological processes and changes in community composition. Our results show that intraspecific effects are often comparable to, and sometimes stronger than, species effects. Species effects tend to be larger for direct ecological responses (for example, through consumption), whereas intraspecific effects and species effects tend to be similar for indirect responses (for example, through trophic cascades). Intraspecific effects are especially strong when indirect interactions alter community composition. Our results summarize data from the first generation of studies examining the relative ecological effects of intraspecific variation. Our conclusions can help inform the design of future experiments and the formulation of strategies to quantify and conserve biodiversity.

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Conservation Association) C/BAR grant from the Canadian Circumpolar Institute NSERC Canada Natural Sciences and Engineering Research Council (NSERC) Miami Univ, Dept Biol, Oxford, OH 45056 USA Univ Wisconsin, Ctr Limnol, Madison, WI 53706 USA Univ South Carolina, Baruch Marine Field Lab, Georgetown, SC USA Univ Western Australia, Ctr Neonatal Res & Educ, Perth, WA 6009, Australia Univ Alabama, Dept Biol Sci, Tuscaloosa, AL 35487 USA Miami Univ, Dept Biol, Hamilton, OH 45011 USA Univ Oslo, Nat Hist Museum, POB 1172, NO-0318 Oslo, Norway Univ Paul Sabatier, Lab Evolut & Diversite Biol, F-31062 Toulouse, France Virginia Commonwealth Univ, Dept Biol, Richmond, VA 23284 USA Univ Fed Rio Grande do Norte, Dept Ecol, Natal, RN, Brazil Univ Georgia, Odum Sch Ecol, Athens, GA 30602 USA Auburn Univ, Dept Biol Sci, Auburn, AL 36849 USA Univ Massachusetts, Sch Environm, Boston, MA 02125 USA British Antarctic Survey, High Cross, Cambridge CB3 0ET, England Ohio Dept Nat Resources, Div Wildlife, Inland Fisheries Res Unit, 10517 Canal Rd SE, Hebron, OH 43025 USA Montana State Univ, Dept Ecol, Bozeman, MT 59717 USA Ohio State Univ, Dept Ecol Evolut & Organismal Biol, Columbus, OH 43210 USA Rivers Sch, 333 Winter St, Boston, MA 02493 USA Inst Marine Res, POB 1870, N-5817 Bergen, Norway Univ St Thomas, Dept Biol, St Paul, MN 55105 USA Univ Arkansas, Dept Biol Sci, Fayetteville, AR 72701 USA Norwegian Inst Water Res, Gaustadalleen 21, NO-0349 Oslo, Norway Cornell Univ, Dept Ecol & Evolutionary Biol, Ithaca, NY 14853 USA Kansas State Univ, Div Biol, Ackert Hall, Manhattan, KS 66506 USA IRSN, LRD, SERIS, PRP ENV,Lab Radioprot, Rue Max Pol Fouchet BP10, F-50130 Octeville, France Univ Fed Mato Grosso do Sul, CCBS, Lab Ecol, Campo Grande, MS, Brazil Fed Off Environm FOEN, Water Div, CH-3003 Bern, Switzerland Univ Wyoming, Dept Zool & Physiol, Laramie, WY 82071 USA Sao Paulo State Univ, Inst Biosci, Dept Zool, BR-18618689 Botucatu, SP, Brazil Minnesota Dept Nat Resources, Fisheries Res, 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Rd,Private Bag 9019, Whangarei 0110, New Zealand Caravan Lab, 5729 36th Ave NE, Seattle, WA 98105 USA Swedish Univ Agr Sci, Dept Aquat Resources, Inst Coastal Res, S-74242 Oregrund, Sweden Muller Sars Soc, Free Basic Res, POB 5831, N-0308 Oslo, Norway Mediterranean Inst Oceanog, 235 Campus Luminy Case 901, F-13288 Marseille 09, France Univ Nacl La Pampa, Fac Ciencias Exactas & Nat, Dept Recursos Nat, Uruguay 151, RA-6300 Santa Rosa, La Pampa, Argentina Yale Univ, Dept Ecol & Evolutionary Biol, New Haven, CT 06520 USA Weizmann Inst Sci, Dept Mol Cell Biol, IL-7610001 Rehovot, Israel Virginia Wesleyan Coll, Dept Biol, Norfolk, VA 23502 USA Univ Minnesota, Math Sci & Technol Dept, Crookston, MN 56716 USA Cary Inst Ecosyst Studies, Millbrook, NY 12545 USA US Geol Survey, Patuxent Wildlife Res Ctr, SO Conte Anadromous Fish Lab, Turners Falls, MA 01376 USA Pyhajarvi Inst, Sepantie 7, FI-27500 Kauttua, Finland USDA ARS, Natl Sedimentat Lab, Water Qual & Ecol Res Unit, 598 McElroy Dr, Oxford, MS 38655 USA Nebraska Wesleyan Univ, Cooper Fdn Ctr Acad Resources, Lincoln, NE 68504 USA Univ Pittsburgh, Dept Microbiol & Mol Genet, Pittsburgh, PA 15219 USA Tohoku Univ, Grad Sch Life Sci, Aoba Ku, 6-3 Aramaki, Sendai, Miyagi 9808578, Japan Hiroshima Univ, Grad Sch Biosphere Sci, 4-4 Kagamiyama 1 Chome, Higashihiroshima 7398528, Japan Univ Montpellier, CNRS, Lab Biodiversite Marine & Ses Usages, F-34095 Montpellier, France Southern Illinois Univ, Dept Zool, Carbondale, IL 62901 USA Southern Illinois Univ, Ctr Ecol, Carbondale, IL 62901 USA Univ Idaho, Dept Fish & Wildlife Sci, Moscow, ID 83844 USA Agr & Agri Food Canada, Brandon Res Ctr, POB 1000A,RR 3, Brandon, MB R7A 5Y3, Canada Trent Univ, Dept Biol, Peterborough, ON K9L 0G2, Canada Polar Field Serv Inc, 8100 Shaffer Pkwy 100, Littleton, CO 80127 USA Kansas State Univ, US Geol Survey, Kansas Cooperat Fish & Wildlife Res Unit, Div Biol, Manhattan, KS 66506 USA Sao Paulo State Univ, Inst Biosci, Dept Zool, BR-18618689 Botucatu, SP, Brazil US National Science Foundation (NSF) OPUS (Opportunities for Promoting Understanding through Synthesis) award: DEB 0918993 NSF: DEB-1030242 CNPq: 304621/2015-3 NSF DDEP grant: 0951432 Ohio Lake Erie Protection Fund: SG189-02 United States Environmental Protection Agency: GL-97590101 Federal Aid in Sport Fish Restoration Program: F-69-P Carrying Capacity in Norwegian Aquaculture (CANO) - Research Council of Norway: 173537 New Zealand Ministry of Business, Innovation and Employment: UOWX0505 St. Johns River Water Management District (Florida): SK933AA US EPA STAR Fellowship: FP-91694301-1 Japan Society for the Promotion of Science KAKENHI: 15H02642 EU BioFresh project, 7th Framework European program: 226874 NSERC: 89673S

Summary Hippopotami can play a significant role as ecosystem engineers and may play an important role as carbon and nutrient vectors from savanna grasslands to aquatic systems. We coupled the results of a feeding study of captive hippopotami, faeces leaching/mineralisation experiments, hippopotamus consumption estimates and the stoichiometry of savanna grasses to calculate excretion and egestion rates of hippopotami. We then used time budgets and population estimates to calculate nutrient loading by hippopotami in the Mara River, Kenya. In captivity, hippopotami consumed 11.0 g dry matter (DM) kg hippopotamus−1 day−1 (110.6 C; 6.8 N; 1.0 P) and egested 5.3 g DM kg−1 day−1. They excreted or egested 2.72 g C, 0.28 g N and 0.04 g P kg hippopotamus−1 day−1, and urine comprised 12% of C, 70% of N and 33% of P of total excretion and egestion. By integrating data from previously published work on hippopotamus digestion with the data we collected in the field, we estimated an average hippopotamus in the Mara River would excrete or egest 1.93–3.58 g DM, 0.78–1.47 g C, 0.13–0.19 g N and 0.01–0.02 g P kg hippopotamus−1 day−1, and that half of this excretion/egestion would enter the river. The hippopotamus population increased by 1500% inside the Maasai Mara National Reserve, Kenya, between 1959 and 2006. We estimate that hippopotami egest 36 200 kg faeces day−1 into the Mara River (wet mass). Daily loading into the river by excretion and egestion equals 8563 kg DM, 3499 kg C, 492 kg N and 48 kg P, which is equivalent to 670% of CPOM, 15% of DOC, 27% of TN and 29% of TP of loading from the upstream catchment. This research provides the first estimates for hippopotamus inputs to rivers that include both excretion and egestion and provides evidence that hippopotami are important resource vectors in sub-Saharan African rivers, even when compared to other sources of carbon and nutrients.

Animal contributions to ecosystem productivity via nutrient regeneration are increasingly recognized as significant for ecosystem productivity. The paradigm in coastal upwelling systems, in contrast, remains centered around the idea that nutrient supply is extrinsic and sourced from deep water. Here we tested for both animal contributions to nitrogen regeneration and microbial retention of nitrogen along a gradient of animal abundance in Washington State, USA. Using inferences from the concentration and isotopic composition of nitrogen forms, as well as the stable nitrogen isotopic composition of particulate organic matter, and plant and animal tissue, we found increased ammonium as well as greater stable nitrogen isotope values in these organisms in areas of increased animal abundance. We further tested the effect of the nearshore biota by comparing it with an immediately adjacent offshore area, and found an enriched δ15N value for nitrate and particulate organic matter. Further, an analysis of the dual ...

SUMMARY 1. Ecological experiments showing large effects are predicted to drive contemporary trait changes resulting from evolution and phenotypic plasticity. However, few classic ecological experiments conducted in the wild have been investigated for evidence of contemporary trait change. 2. We examined a classic experiment in trophic ecology, the introduction of alewife (Alosa pseudoharengus) to Crystal Lake, Connecticut, U.S.A. (Brooks & Dodson, 1965), for the presence of contemporary trait change. 3. Alewife were introduced to Crystal Lake, an inland lake isolated from the coastal ocean, from an anadromous (migratory sea-run) source population. We utilised museum specimens collected soon after introduction and modern samples to measure changes in gill-raker morphology for the Crystal Lake alewife population since its introduction. We compared the gill-rakers of the Crystal Lake population to those of other nearby anadromous and landlocked (freshwater resident) alewife populations. 4. At introduction, the Crystal Lake population showed gill-raker spacing (GRS) similar to that of anadromous populations. Following introduction, we found evidence for a rapid decrease in GRS, an important trait for size-selective prey capture in fishes. This decrease occurred alongside a dramatic decline in zooplankton size, shown by Brooks and Dodson (1965) to be caused by the onset of alewife predation. After 45 years of isolation in freshwater, the Crystal Lake population showed GRS typical of landlocked populations. 5. Brooks and Dodson’s study is a classic example of the strong effects predators can have on prey communities. Our study shows that such community effects of predators may feed back to shape predator trophic morphology. The rate of trait change observed for the Crystal Lake alewife population is comparable to rates observed from evolutionary experiments conducted explicitly to examine trait changes over contemporary time scales. 6. We conclude that strong ecological effects of introduced populations may be important drivers of contemporary trait change. We propose that classic ecological experiments represent underutilised resources for examining interactions between contemporary trait change and ecological effects in the wild.

Benthic communities in Long Island Sound (LIS) have experienced over 150 years of commercial shellfishing and excess nutrient loading (eutrophication) which causes hypoxia. We established an ecological baseline using a combination of live, dead, archaeological, and fossil material to investigate the impacts of these stressors on the molluscan community. We expected that ecological change would increase with eutrophication-hypoxia west towards New York City. Instead we found that taxonomic similarity, rank-order abundance, and drilling frequency are more strongly controlled by commercial fishing pressure than by decreasing dissolved oxygen. Commercial fisherman collecting quahog clams (Mercenaria mercenaria), physically disrupt surface-dwelling organisms and also kill large numbers of predatory gastropods, including the channeled whelk, Busycotypus canaliculatus, and the drilling moonsnails Neverita duplicata and Euspira heros, to protect hard clam stocks. As a result, areas dredged by commercial fishermen yield fewer shells with drill-holes and fewer surface-dwelling organisms than unfished sites. In spite of recent reductions in lobster fishing, crushing predation by crabs and lobsters on clams has been suppressed below baseline levels throughout LIS, even in the well oxygenated east. The absence of a clear relationship between eutrophication-hypoxia and ecological change questions the effectiveness of nitrogen reduction alone as a restoration strategy. LIS fossils revealed a relatively ancient loss of those mollusks associated with seagrass and oyster habitats (e.g., oysters, Crassostrea virginica; jingle shells, Anomia simplex; scallops, Argopecten irradiens; and the gastropod Bittiolum alternatum) that predates the accumulation of dead shells and underscores the need for older material to reveal the shifting baseline. The interactive nature of multiple stressors means that past overfishing may have dampened the response of communities in LIS to eutrophication or inhibited their capactiy to recover. The unexpected role of hypoxic areas protected from commercial fishing as refuges highlights the utility of no-take marine preserves in eutrophied estuaries worldwide.

Rocky intertidal productivity is traditionally thought to be sustained almost solely by upwelled nitrate with remineralized forms of minor importance. Using tidepools as natural experimental mesocosms, we conducted 15N-tracer experiments to test whether ammonium remineralized within the rocky intertidal is also a significant source of fixed N to localized ecosystem production. Comparison of tidepools with and without the dominant bivalve Mytilus californianus allowed consideration of its role in NH+4 cycling. Closed water-incubation bottles were used to investigate the contribution of suspended microbes to NH+4 cycling. Tidepools with mussels had both greater NH+4 remineralization (two times) and NH+4 removal as compared with those without, with daytime rates greater than nighttime rates. Incorporation of NH+4 tracer by particulate organic matter and macroalgae, and the persistence of this signal in tidepools for several days following the experiment, showed retention of autochthonous NH+4 in the system. Remineralization rates were tightly correlated to removal rates when compared over all treatments and experiments, but NH+4 remineralization was significantly greater than removal, suggesting a surplus available to nearshore primary producers.

Contemporary insights from evolutionary ecology suggest that population divergence in ecologically important traits within predators can generate diversifying ecological selection on local community structure. Many studies acknowledging these effects of intraspecific variation assume that local populations are situated in communities that are unconnected to similar communities within a shared region. Recent work from metacommunity ecology suggests that species dispersal among communities can also influence species diversity and composition but can depend upon the relative importance of the local environment. Here, we study the relative effects of intraspecific phenotypic variation in a fish predator and spatial processes related to plankton species dispersal on multitrophic lake plankton metacommunity structure. Intraspecific diversification in foraging traits and residence time of the planktivorous fish alewife (Alosa pseudoharengus) among coastal lakes yields lake metacommunities supporting three lake types which differ in the phenotype and incidence of alewife: lakes with anadromous, landlocked, or no alewives. In coastal lakes, plankton community composition was attributed to dispersal versus local environmental predictors, including intraspecific variation in alewives. Local and beta diversity of zooplankton and phytoplankton was additionally measured in response to intraspecific variation in alewives. Zooplankton communities were structured by species sorting, with a strong influence of intraspecific variation in A. pseudoharengus. Intraspecific variation altered zooplankton species richness and beta diversity, where lake communities with landlocked alewives exhibited intermediate richness between lakes with anadromous alewives and without alewives, and greater community similarity. Phytoplankton diversity, in contrast, was highest in lakes with landlocked alewives. The results indicate that plankton dispersal in the region supplied a migrant pool that was strongly structured by intraspecific variation in alewives. This is one of the first studies to demonstrate that intraspecific phenotypic variation in a predator can maintain contrasting patterns of multitrophic diversity in metacommunities.

A major challenge in conservation biology is the need to broadly prioritize conservation efforts when demographic data are limited. One method to address this challenge is to use population genetic data to define groups of populations linked by migration and then use demographic information from monitored populations to draw inferences about the status of unmonitored populations within those groups. We applied this method to anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), species for which long-term demographic data are limited. Recent decades have seen dramatic declines in these species, which are an important ecological component of coastal ecosystems and once represented an important fishery resource. Results show that most populations comprise genetically distinguishable units, which are nested geographically within genetically distinct clusters or stocks. We identified three distinct stocks in alewife and four stocks in blueback herring. Analysis of available time series data for spawning adult abundance and body size indicate declines across the US ranges of both species, with the most severe declines having occurred for populations belonging to the Southern New England and the Mid-Atlantic Stocks. While all alewife and blueback herring populations deserve conservation attention, those belonging to these genetic stocks warrant the highest conservation prioritization.

Organisms experience competing selective pressures, which can obscure the mechanisms driving evolution. Daphnia ambigua is found in lakes where a predator, the alewife (Alosa pseudoharengus) either does (anadromous) or does not (landlocked) migrate between marine and freshwater. We previously reported an association between alewife variation and life history evolution in Daphnia. However, differences in alewife migration indirectly influence phytoplankton composition for Daphnia. In ‘anadromous lakes’, Daphnia are present in the spring and experience abundant high-quality green algae. Intense predation by young-of-the-year anadromous alewife quickly eliminates these Daphnia populations by early summer. Daphnia from ‘landlocked lakes’ and lakes without alewife (‘no alewife lakes’) are present during the spring and summer and are more likely to experience high concentrations of sub-optimal cyanobacteria during the summer. To explore links between predation, resources, and prey evolution, we reared third-generation laboratory-born Daphnia from all lake types on increasing cyanobacteria concentrations. We observed several significant ‘lake type × resource’ interactions whereby the differences among lake types depended upon cyanobacteria concentrations. Daphnia from anadromous lakes developed faster, were larger at maturation, produced more offspring, and had higher intrinsic rates of increase in the absence of cyanobacteria. Such trends disappeared or reversed as cyanobacteria concentration was increased because Daphnia from anadromous lakes were more strongly influenced by the presence of cyanobacteria. Our results argue that alewife migration and phytoplankton composition both play a role in Daphnia evolution.

Prior to Euro-American contact, anadromous alewives (Alosa pseudoharengus) were abundant throughout eastern North America. In the 400 yr since Euro-American settlement began in the region, anadromous alewife populations have declined by an order of magnitude or more while human land use has simultaneously intensified. Here we asked how lake nutrient inputs in the southern New England region have changed over the past 400 yr by examining nutrient inputs to four lakes in coastal Connecticut that differ in their land-use history and their history of accessibility to anadromous alewife. We estimated the flux of nitrogen and phosphorus from both anadromous alewife and the landscape and conducted a paleoecological analysis of stable isotopes (δ15N, total δ13C, organic δ13C) and nutrients (N : P, C : N, organic C) from lake sediment cores in each of our study watersheds. Nutrient loading models suggest that allochthonous nutrient inputs are now dominated by watershed land use and our paleoecological data also reflect major changes in human land use. Loading models also suggest that prior to Euro-American contact, anadromous alewife runs historically provided up to 95% of allochthonous phosphorus inputs and up to 68% of allochthonous nitrogen inputs to the region's coastal lakes. However, paleoecological data suggest that even the large nutrient inputs from abundant past alewife populations may never have had the same long-term effect on lake nutrient dynamics as those from the landscape due to the unique combination of the alewife's life history and coastal Connecticut's climate and geomorphology.

Intraspecific competition is considered a principal driver of dietary variation, but empirical studies provide mixed support for this mechanism. Here we link comparative and experimental work testing the effects of competition and resource availability on the dietary variation of the alewife (Alosa pseudoharengus). The alewife, a consumer with extreme effects on its resources, was specifically utilized to additionally test the idea that strong interactions between a consumer and its resources can diminish the diversifying effect of competition. First, we compared the short- and long-term diet measures of wild populations across a wide range of densities. Second, in a pair of large-scale field mesocosm experiments, we explored the influence of competition and interaction strength on alewife dietary variation. Results from a whole-lake comparison and field experiments indicated that increasing competition was negatively correlated with population dietary variation. Further, altering the strength of the interaction between the alewife and its prey via prey supplementation eliminated this negative relationship. Collectively, our results suggest that competitive interactions may not drive dietary diversification in the alewife and, potentially, in other highly effective consumers. Our results also indicate that further consideration of the strength of species interactions (and the consumer traits that underlie them) would improve our understanding of the link between intraspecific competition and variation.

Recent work suggests that juvenile alewives (Alosa pseudoharengus) share similar phenotypes among independently derived landlocked (freshwater resident) populations. Based on this observation, it is possible that the alewife life history forms represent a case of parallel adaptive divergence. To further evaluate this hypothesis, we describe patterns of body shape divergence between anadromous and landlocked alewife life history forms using geometric morphometrics. Our results suggest that body shape differs significantly between juveniles of the alewife forms: anadromous fish were more robust, with larger heads and deeper caudal peduncles, while landlocked fish from three independently isolated populations were more fusiform with thinner caudal peduncles and smaller heads. These differences matched population level dietary patterns, which suggest that anadromous fish consumed more littoral resources than landlocked fish. Finding consistent differences across populations of the same form supports the notion that landlocked alewives have diverged from their anadromous ancestors in a parallel manner, in response to pressures associated with being isolated in freshwater lakes. Comparing alewife phenotypes to expectations from the literature suggests that neither migration distance of the population, nor the relative availability of habitats in each lake, are likely drivers of the pattern we report. Instead, the pattern is consistent with the hypothesis that divergence between alewife forms results from the distinct effects of each form on its zooplankton prey.

Predation has important cascading impacts on primary producer biomass and community composition in many ecosystems. While most studies have focused on the consequences of interspecific or density differences in predators, it is recognized that phenotypic variation within species can have strong and cascading community and ecosystem consequences at lower trophic levels. In coastal New England lakes, both the presence and life history form of the zooplanktivorous fish alewife, Alosa pseudoharengus, have strong influence on the biomass, size structure and community composition of crustacean zooplankton communities. Here we test the hypothesis that alewife presence and life history will have cascading impacts on phytoplankton biomass and community composition in a mesocosm experiment that previously reported strong biomass and compositional differences of crustacean zooplankton communities among alewife treatments. We show that alewife life history led to small but statistically significant differences in phytoplankton community composition among treatments. This compositional difference was driven primarily by an increase in the density of two edible phytoplankton genera associated with lower zooplankton biomass in the anadromous alewife treatment. Our results show that intraspecific variation in a predator can have cascading effects on primary producer communities. However we did not observe significant differences in total algal biomass.

We tested the use of cladoceran remains as a proxy for the presence and life history type of alewife (Alosa pseudoharengus) from pre-colonial times to present in a group of coastal lakes in southern New England. Alewife are a keystone predator that structure the zooplankton community through strong predation on large-bodied zooplankton species, which releases small zooplankton species, such as Bosmina spp., from competition and predation pressure. In southern New England there are lakes without alewife, lakes with anadromous alewife that only reside in lakes during the summer, and lakes with landlocked alewife that reside in lakes year-round. The entire zooplankton commu- nity of these lakes is structured differently based on the presence and type of alewife they contain. We examined differences in the morphology of Bosmina spp. from sediment core samples and contemporary zooplankton samples between lakes with different types of alewife. We found that there were significant differences in the morphology of Bosmina spp. between lakes with and without alewife. We also used discriminant analysis on the morphology of Bosmina spp. to classify lakes in terms of alewife presence and alewife type. We found that the morphology of Bosmina spp. can serve as a useful proxy for detecting the presence, but not the life history type of alewife from paleoecological and contemporary inferences.

The Mara River Basin in East Africa is a trans-boundary basin of international significance experiencing excessive levels of sediment loads. Sediment levels in this river are extremely high (turbidities as high as 6,000 NTU) and appear to be increasing over time. Large wildlife populations, unregulated livestock grazing, and agricultural land conversion are all potential factors increasing sediment loads in the semi-arid portion of the basin. The basin is well-known for its annual wildebeest (Connochaetes taurinus) migration of approximately 1.3 million individuals, but it also has a growing population of hippopotami (Hippopotamus amphibius), which reside within the river and may contribute to the flux of suspended sediments. We used in situ pressure transducers and turbidity sensors to quantify the sediment flux at two sites for the Mara River and investigate the origin of riverine suspended sediment. We found that the combined Middle Mara—Talek catchment, a relatively flat but semi-arid region with large populations of wildlife and domestic cattle, is responsible for 2/3 of the sediment flux. The sediment yield from the combined Middle Mara–Talek catchment is approximately the same as the headwaters, despite receiving less rainfall. There was high monthly variability in suspended sediment fluxes. Although hippopotamus pools are not a major source of suspended sediments under baseflow, they do contribute to short-term variability in suspended sediments. This research identified sources of suspended sediments in the Mara River and important regions of the catchment to target for conservation, and suggests hippopotami may influence riverine sediment dynamics.

Environmental signals can induce phenotypic changes that span multiple generations. Along with phenotypic responses that occur during development (i.e. ‘within-generation’ plasticity), such ‘transgenerational plasticity’ (TGP) has been documented in a diverse array of taxa spanning many environmental perturbations. New theory predicts that temporal stability is a key driver of the evolution of TGP. We tested this prediction using natural populations of zooplankton from lakes in Connecticut that span a large gradient in the temporal dynamics of predator-induced mortality. We reared more than 120 clones of Daphnia ambigua from nine lakes for multiple generations in the presence/absence of predator cues. We found that temporal variation in mortality selects for within-generation plasticity while consistently strong (or weak) mortality selects for increased TGP. Such results provide us the first evidence for local adaptation in TGP and argue that divergent ecological conditions select for phenotypic responses within and across generations.

Food-chain length is an important character of ecological communities that affects many of their functional aspects. Recently, an increasing number of studies have tested the effects of productivity, disturbance, or ecosystem size on food-chain length in a variety of natural systems. Here we conduct a formal meta-analysis to summarize findings from these empirical studies. We found significant positive mean effects of productivity and ecosystem size but no significant mean effect of disturbance on food-chain length. The strength of mean effect sizes was not significantly different between productivity and ecosystem size. These results lend general support to previous theories predicting the effect of productivity and ecosystem size, but fail to support the prediction that disturbance shortens food chains. In addition, our meta-analysis found that the effect sizes of primary studies were significantly heterogeneous for ecosystem size and disturbance, but not for productivity. This pattern might reflect that ecosystem size and disturbance can affect food-chain length through multiple different mechanisms, while productivity influences food-chain length in a simple manner through energy limitation.