Changing temperature can substantially shift ecological communities by altering the strength and stability of trophic interactions. Because many ecological rates are constrained by temperature, new approaches are required to understand how simultaneous changes in multiple rates alter the relative performance of species and their trophic interactions. We develop an energetic approach to identify the relationship between biomass fluxes and standing biomass across trophic levels. Our approach links ecological rates and trophic dynamics to measure temperature-dependent changes to the strength of trophic interactions and determine how these changes alter food web stability. It accomplishes this by using biomass as a common energetic currency and isolating three temperature-dependent processes that are common to all consumer-resource interactions: biomass accumulation of the resource, resource consumption and consumer mortality. Using this framework, we clarify when and how temperature alters consumer to resource biomass ratios, equilibrium resilience, consumer variability, extinction risk and transient vs. equilibrium dynamics. Finally, we characterise key asymmetries in species responses to temperature that produce these distinct dynamic behaviours and identify when they are likely to emerge. Overall, our framework provides a mechanistic and more unified understanding of the temperature dependence of trophic dynamics in terms of ecological rates, biomass ratios and stability.
Phenological responses to climate change (e.g., earlier leaf-out or egg hatch date) are now well documented and clearly linked to rising temperatures in recent decades. Such shifts in the phenologies of interacting species may lead to shifts in their synchrony, with cascading community and ecosystem consequences. To date, single-system studies have provided no clear picture, either finding synchrony shifts may be extremely prevalent [Mayor SJ, et al. (2017) 7:1902] or relatively uncommon [Iler AM, et al. (2013) 19:2348-2359], suggesting that shifts toward asynchrony may be infrequent. A meta-analytic approach would provide insights into global trends and how they are linked to climate change. We compared phenological shifts among pairwise species interactions (e.g., predator-prey) using published long-term time-series data of phenological events from aquatic and terrestrial ecosystems across four continents since 1951 to determine whether recent climate change has led to overall shifts in synchrony. We show that the relative timing of key life cycle events of interacting species has changed significantly over the past 35 years. Further, by comparing the period before major climate change (pre-1980s) and after, we show that estimated changes in phenology and synchrony are greater in recent decades. However, there has been no consistent trend in the direction of these changes. Our findings show that there have been shifts in the timing of interacting species in recent decades; the next challenges are to improve our ability to predict the direction of change and understand the full consequences for communities and ecosystems.
Biological responses to climate change have been widely documented across taxa and regions, but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. Here we reviewed 10,090 abstracts and extracted data from 71 studies reported in 58 relevant publications, to assess quantitatively whether phenotypic trait changes associated with climate change are adaptive in animals. A meta-analysis focussing on birds, the taxon best represented in our dataset, suggests that global warming has not systematically affected morphological traits, but has advanced phenological traits. We demonstrate that these advances are adaptive for some species, but imperfect as evidenced by the observed consistent selection for earlier timing. Application of a theoretical model indicates that the evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species.
Global change has made it important to understand the factors that shape species' distributions. Central to this area of research is the question of whether species' range limits primarily reflect the distribution of suitable habitat (i.e. niche limits) or arise as a result of dispersal limitation. Over-the-edge transplant experiments and ecological niche models are commonly used to address this question, yet few studies have taken advantage of a combined approach for inferring the causes of range limits. Here, we synthesise results from existing transplant experiments with new information on the predicted suitability of sites based on niche models. We found that individual performance and habitat suitability independently decline beyond range limits across multiple species. Furthermore, inferences from transplant experiments and niche models were generally concordant within species, with 31 out of 40 cases fully supporting the hypothesis that range limits are niche limits. These results suggest that range limits are often niche limits and that the factors constraining species' ranges operate at scales detectable by both transplant experiments and niche models. In light of these findings, we outline an integrative framework for addressing the causes of range limits in individual species.
, but recent studies showing the importance of plant genetic diversity for herbivores suggest that plant trait variance may be equally important 5,6 . The consequences of plant trait variance for herbivore performance, however, have been largely overlooked. Here we report an extensive assessment of the effects of withinpopulation plant trait variance on herbivore performance using 457 performance datasets from 53 species of insect herbivores. We found that variance in plant nutritive traits substantially reduces mean herbivore performance via nonlinear averaging of performance relationships that were overwhelmingly concave-down. In contrast, relationships between herbivore performance and plant defense levels were typically linear, such that plant defense variance does not affect herbivore performance via nonlinear averaging. Our results demonstrate that plants contribute to the suppression of herbivore populations by having variable nutrient levels, not just by having low average quality as is typically thought. We propose that this phenomenon could play a key role in the suppression of herbivore populations in natural systems, and that increased nutrient heterogeneity within agricultural crops could contribute to the sustainable control of insect pests in agroecosystems.Decades of research have established the importance of plant nutritive and defensive traits for herbivore performance and population dynamics 1 . Recent studies, showing that plant genetic diversity influences herbivore community patterns, suggest that plants influence herbivores not just through average trait values but also through variance in trait values 5,6 . The literature on plant defenses and herbivore nutritional ecology, however, focuses on mean relationships and mostly ignores the consequences of trait variance 2,3 . This is an oversight because intraspecific plant trait variance pervades natural systems, from among tissues within individuals to among individuals within populations 4 . In modern agroecosystems, however, plant functional diversity has been replaced by extensive homogeneous monocultures of single crop varieties or genotypes 7 . How the loss of trait diversity influences higher trophic levels and ecosystems services like pest control is unexplored relative to how much is known about the consequences of genetic diversity 8,9 . Elucidation of the direct effects of variability in plant defensive or nutritive traits on herbivore performance would inform management of agroecosystems-perhaps revealing new ways to use crop heterogeneity for sustainable pest management-and advance our fundamental understanding of plant-insect interactions. Here we test for general patterns in the effects of plant trait variance on herbivore performance using 457 datasets relating plant traits to herbivore growth and survival for 53 species of phytophagous insects from seven orders.Plant variance could influence herbivores in several ways, including reducing the opportunity for herbivore populations to adapt evolutionarily to plant defenses 10 ....
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