Trophic structure alters consequences of environmental warming

Competition Increases Risk of Species Extinction during Extreme Warming

AbstractTemperature and interspecific competition are fundamental drivers of community structure in natural systems and can interact to affect many measures of species performance. However, surprisingly little is known about the extent to which competition affects extinction temperatures during extreme warming. This information is important for evaluating future threats to species from extreme high-temperature events and heat waves, which are rising in frequency and severity around the world. Using experimental freshwater communities of rotifers and ciliates, this study shows that interspecific competition can lower the threshold temperature at which local extinction occurs, reducing time to extinction during periods of sustained warming by as much as 2 weeks. Competitors may lower extinction temperatures by altering biochemical characteristics of the natural environment that affect temperature tolerance (e.g., levels of dissolved oxygen, nutrients, and metabolic wastes) or by accelerating population decline through traditional effects of resource depletion on life history parameters that affect population growth rates. The results suggest that changes in community structure in space and time could drive variability in upper thermal limits.

Legacy effects in temporally separated tadpole species are not mediated by invasive Western Mosquitofish (Gambusia affinis)

Temporally separated species are often thought to have limited competition over a shared resource. However, early arriving species may consume a limited resource such that later-arriving species have access to fewer resources and thus experience competitive effects, even if they are temporally separated (i.e., they experience legacy effects from the early species). The presence of a predator might affect potential legacy effects by influencing the behavior or survivorship of the early species. Using a mesocosm experiment, I examined whether the presence of nonnative Western Mosquitofish (Gambusia affinis) mediated legacy effects in the interaction of two temporally separated species of tadpoles, early arriving American Toads (Anaxyrus americanus) and late-arriving Bullfrogs (Rana catesbeiana). Anaxyrus americanus tadpoles reduced R. catesbeiana tadpole growth despite all A. americanus tadpoles metamorphosing 8 days before the introduction of R. catesbeiana tadpoles into the mesocosms (i.e., legacy effects). Gambusia affinis had limited effects on A. americanus (1 day delay in metamorphosis but no effect on survivorship or size at metamorphosis) and positive effects on R. catesbeiana (increased growth). There were no significant interactions between the A. americanus tadpole density and G. affinis treatments. In conclusion, I found evidence of significant legacy effects of A. americanus tadpoles on R. catesbeiana tadpoles, but no evidence that G. affinis mediated the legacy effects.

Linking animal behavior to ecosystem change in disturbed environments

Environmental disturbances often cause individuals to change their behavior. The behavioral responses can induce a chain of reactions through the network of species interactions, via consumptive and trait mediated connections. Given that species interactions define ecosystem structure and functioning, changes to these interactions often have ecological repercussions. Here, we explore the transmission of behavioral responses through the network of species interactions, and how the responses influence ecological conditions. We describe the underlying mechanisms and the ultimate impact that the behavioral responses can have on ecosystem structure and functioning, including biodiversity and ecosystems stability and services. We explain why behavioral responses of some species have a larger impact than that of others on ecosystems, and why research should focus on these species and their interactions. With the work, we synthesize existing theory and empirical evidence to provide a conceptual framework that links behavior responses to altered species interactions, community dynamics, and ecosystem processes. Considering that species interactions link biodiversity to ecosystem functioning, a deeper understanding of behavioral responses and their causes and consequences can improve our knowledge of the mechanisms and pathways through which human activities alter ecosystems. This knowledge can improve our ability to predict the effects of ongoing disturbances on communities and ecosystems and decide on the interventions needed to mitigate negative effects.

Effects of Warming on Intraguild Predator Communities with Ontogenetic Diet Shifts

AbstractSpecies interactions mediate how warming affects community composition via individual growth and population size structure. While predictions on how warming affects composition of size- or stage-structured communities have so far focused on linear (food chain) communities, mixed competition-predation interactions, such as intraguild predation, are common. Intraguild predation often results from changes in diet over ontogeny ("ontogenetic diet shifts") and strongly affects community composition and dynamics. Here, we study how warming affects a community of intraguild predators with ontogenetic diet shifts, consumers, and shared prey by analyzing a stage-structured bioenergetics multispecies model with temperature- and body size-dependent individual-level rates. We find that warming can strengthen competition and decrease predation, leading to a loss of a cultivation mechanism (the feedback between predation on and competition with consumers exerted by predators) and ultimately predator collapse. Furthermore, we show that the effect of warming on community composition depends on the extent of the ontogenetic diet shift and that warming can cause a sequence of community reconfigurations in species with partial diet shifts. Our findings contrast previous predictions concerning individual growth of predators and the mechanisms behind predator loss in warmer environments and highlight how feedbacks between temperature and intraspecific size structure are important for understanding such effects on community composition.

Temperature variability alters the stability and thresholds for collapse of interacting species

Temperature variability and extremes can have profound impacts on populations and ecological communities. Predicting impacts of thermal variability poses a challenge, because it has both direct physiological effects and indirect effects through species interactions. In addition, differences in thermal performance between predators and prey and nonlinear averaging of temperature-dependent performance can result in complex and counterintuitive population dynamics in response to climate change. Yet the combined consequences of these effects remain underexplored. Here, modelling temperature-dependent predator-prey dynamics, we study how changes in temperature variability affect population size, collapse and stable coexistence of both predator and prey, relative to under constant environments or warming alone. We find that the effects of temperature variation on interacting species can lead to a diversity of outcomes, from predator collapse to stable coexistence, depending on interaction strengths and differences in species' thermal performance. Temperature variability also alters predictions about population collapse-in some cases allowing predators to persist for longer than predicted when considering warming alone, and in others accelerating collapse. To inform management responses that are robust to future climates with increasing temperature variability and extremes, we need to incorporate the consequences of temperature variation in complex ecosystems. This article is part of the theme issue 'Integrative research perspectives on marine conservation'.

Individual variation and interactions explain food web responses to global warming

Understanding food web responses to global warming, and their consequences for conservation and management, requires knowledge on how responses vary both among and within species. Warming can reduce both species richness and biomass production. However, warming responses observed at different levels of biological organization may seem contradictory. For example, higher temperatures commonly lead to faster individual body growth but can decrease biomass production of fishes. Here we show that the key to resolve this contradiction is intraspecific variation, because (i) community dynamics emerge from interactions among individuals, and (ii) ecological interactions, physiological processes and warming effects often vary over life history. By combining insights from temperature-dependent dynamic models of simple food webs, observations over large temperature gradients and findings from short-term mesocosm and multi-decadal whole-ecosystem warming experiments, we resolve mechanisms by which warming waters can affect food webs via individual-level responses and review their empirical support. We identify a need for warming experiments on food webs manipulating population size structures to test these mechanisms. We stress that within-species variation in both body size, temperature responses and ecological interactions are key for accurate predictions and appropriate conservation efforts for fish production and food web function under a warming climate.

This article is part of the theme issue ‘Integrative research perspectives on marine conservation'.

Temperature-dependent competitive advantages of an allelopathic alga over non-allelopathic alga are altered by pollutants and initial algal abundance levels

In the context of climate warming, the dominance of allelopathic algae that cause ecosystem disturbances is an important topic. Although the hypothesis that an increase in temperature will be favorable to the dominance of allelopathic algae has been increasingly supported by many studies, it is still unclear how other factors can affect the influence of temperature. In this study, the effects of copper exposure and initial algal abundance on the competition between Pseudokirchneriella subcapitata (non-allelopathic alga) and Chlorella vulgaris (allelopathic alga) were investigated during temperature changes. The results showed that increased temperatures enhanced the competitive advantage of C. vulgaris only in the absence of copper exposure. Our data confirmed that copper exposure along with increased temperature (20-30 °C) may change the competitive advantage of C. vulgaris from favorable to unfavorable. The initial algal abundance was found to affect competition outcome by controlling copper toxicity. This study suggests that pollutants and initial abundance can alter the effects of increased temperature on the allelopathic interaction. Given the temporal dynamics of algal abundance and the pollutants in natural ecosystems, these findings should be considered in the prediction of temperature influence on an algal community.

Prey-predator phenological mismatch under climate change

Insect phenology is affected by climate change and main responses are driven by phenotypic plasticity and evolutionary changes. Any modification in seasonal activity in one species can have consequences on interacting species, within and among trophic levels. In this overview, we focus on synchronisation mismatches that can occur between tightly interacting species such as hosts and parasitoids or preys and predators. Asynchronies happen because species from different trophic levels can have different response rates to climate change. We show that insect species alter their seasonal activities by modifying their life-cycle through change in voltinism or by altering their development rate. We expect strong bottom-up effects for phenology adjustments rather than top-down effects within food-webs. Extremely complex outcomes arise from such trophic mismatches, which make consequences at the community or ecosystem levels tricky to predict in a climate change context. We explore a set of potential consequences on population dynamics, conservation of species interactions, with a particular focus on the provision of ecosystem services by predators and parasitoids, such as biological pest control.

Species interactions under climate change: connecting kinetic effects of temperature on individuals to community dynamics

Human-induced climate change, dominated by warming trends, poses a major threat to global biodiversity and ecosystem functioning. Species interactions relay the direct and indirect effects of climate warming on individuals to communities, and detailed understanding across these levels is crucial to predict ecological consequences of climate change. We provide a conceptual framework that links temperature effects on insect physiology and behaviour to altered species interactions and community dynamics. We highlight key features of this framework with recent studies investigating the impacts of warming climate on insects and other ectotherms and identify methodological, taxonomic and geographic biases. While the effects of increased constant temperatures are now well understood, future studies should focus on temperature variation, interactions with other stressors and cross-system comparisons.