Ecological Monographs最新文献

The addition of terrestrial inputs to the ocean can have cascading impacts on coastal biogeochemistry by directly altering the water chemistry and indirectly changing ecosystem metabolism, which also influences water chemistry. Here, we use submarine groundwater discharge (SGD) as a model system to examine the direct geochemical and indirect biologically mediated effects of terrestrial nutrient subsidies on a fringing coral reef. We hypothesize that the addition of new solutes from SGD alters ecosystem metabolic processes including net ecosystem production and calcification, thereby changing the patterns of uptake and release of carbon by benthic organisms. SGD is a common land–sea connection that delivers terrestrially sourced nutrients, carbon dioxide, and organic matter to coastal ecosystems. Our research was conducted at two distinct coral reefs in Moʻorea, French Polynesia, characterized by contrasting flow regimes and SGD biogeochemistry. Using a Bayesian structural equation model, our research elucidates the direct geochemical and indirect biologically mediated effects of SGD on both dissolved organic and inorganic carbon pools. We reveal that SGD-derived nutrients enhance both net ecosystem production and respiration. Furthermore, the study demonstrates that SGD-induced alterations in net ecosystem production significantly influence pH dynamics, ultimately impacting net ecosystem calcification. Notably, the study underscores the context-dependent nature of these cascading direct and indirect effects resulting from SGD, with flow conditions and the composition of the terrestrial inputs playing pivotal roles. Our research provides valuable insights into the interplay between terrestrial inputs and coral reef ecosystems, advancing our understanding of coastal carbon cycling and the broader implications of allochthonous inputs on ecosystem functioning.

Animal populations in arid environments, where extreme temperatures and erratic rainfall are normal, are particularly vulnerable to climate change. While numerous studies have examined the effects of temperature and rainfall on the breeding success and survival of arid-zone species, the mechanistic pathways linking climate variation to demography remain poorly described for most species. Using long-term data from meerkats (Suricata suricatta) in the Kalahari Desert, we show that increases in rainfall and primary productivity (as measured by normalized difference vegetation index) were associated with improved foraging success, daily body mass gain, and body condition, which in turn contributed to enhanced breeding success and survival. Conversely, high summer temperatures were associated with reduced foraging performance and body condition. Foraging efficiency declined when daily maximum summer temperatures exceeded 35°C, and at temperatures above 37°C, diurnal mass gains often failed to offset overnight mass losses. While high temperatures had short-term detrimental effects, runs of hot days were relatively infrequent and often coincided with periods of high primary productivity. As a result, individuals were rarely in poor condition during the hottest periods of the year, suggesting that they could recover any mass lost on hot days during subsequent cooler periods. Only when high temperatures persisted alongside low primary productivity did body condition drop sharply. Although temperature variation has not yet affected the demography of our meerkat population as strongly as rainfall variation, further warming in the region and the potential for more frequent and severe hot droughts are likely to have major implications for the species' distribution and persistence. Our study emphasizes the need to consider both rainfall and temperature variations across seasons, as well as their interactions, to better understand and predict the impacts of climate change on arid-zone animals. It also demonstrates the value of long-term, high-resolution behavioral and physiological data, including frequent, year-round weighing of animals, in establishing causal links between climate and demography.

Trait-based ecology, a prominent research field identifying traits linked to the distribution and interactions of organisms and their impact on ecosystem functioning, has flourished in the last three decades. Yet, the field still grapples with critical challenges, broadly framed as Raunkiæran shortfalls. Recognizing and interconnecting these limitations is vital for designing and prioritizing research objectives and mainstreaming trait-based approaches across a variety of organisms, trophic levels, and biomes. This strategic review scrutinizes eight major limitations within trait-based ecology, spanning scales from organisms to the entire biosphere. Challenges range from defining and measuring traits (SF 1), exploring intraspecific variability within and across individuals and populations (SF 2), understanding the complex relationships between trait variation and fitness (SF 3), and discerning trait variations with underlying evolutionary patterns (SF 4). This review extends to community assembly (SF 5), ecosystem functioning and multitrophic relationships (SFs 6 and 7), and global repositories and scaling (SF 8). At the core of trait-based ecology lies the ambition of scaling up processes from individuals to ecosystems by exploring the ecological strategies of organisms and connecting them to ecosystem functions across multiple trophic levels. Achieving this goal necessitates addressing key limitations embedded in the foundations of trait-based ecology. After identifying key SFs, we propose pathways for advancing trait-based ecology, fortifying its robustness, and unlocking its full potential to significantly contribute to ecological understanding and biodiversity conservation. This review underscores the significance of systematically evaluating the performance of organisms in standardized conditions, encompassing their responses to environmental variation and effects on ecosystems. This approach aims to bridge the gap between easily measurable traits, species ecological strategies, their demography, and their combined impacts on ecosystems.

Biodiversity is a central concept in ecology and biology. Its underpinnings are multifaceted and complex and involve multiple spatiotemporal scales, and many ways of measuring relevant characteristics. Its comprehensive understanding requires a framework on which to organize concepts and associated metrics. The analysis of biodiversity is based on combinations of two types of units: study units (i.e., the inferential domain in time and space that characterizes sampling) and measurement units (i.e., metrics). We provide an integrated framework for the units of study derived from three aspects of organisms: their spatiotemporal relationships (geography), their evolutionary relationships (phylogeny), and their ecological relationships based on their requirements and effects (niche). We systematize the units of measurement based on four types of data (identity, abundance, phylogeny, traits), two properties of those data (magnitude and variability), and three approaches for their measurement (total, pairwise, nearest neighbor). Together, they define 14 basic elements that can be combined in many ways and be subject to various mathematical operations. The result is 130 different metrics, including those in the literature and those developed herein. We propose standardized symbols for these metrics and provide formulas using standard notations for their parameters. Importantly, we show how our framework can be used to align study units and measurement units with questions concerning the causes and consequences of biodiversity. We provide case studies on bats in Peru and trees in the eastern United States to ecological gradient theory, niche theory, and theory about relationships between biodiversity and productivity, and we discuss which metrics might be most appropriate in tests of island biogeography theory and the dilution effect of pathogen transmission. Our key recommendations are that researchers should: (1) harmonize study unit properties with explicitly defined questions, (2) couple metric properties with underlying processes, and (3) compare metrics with similar properties. By providing an overarching framework that clearly delineates units of study and units of measurement, we hope to ensure that appropriate data are applied to particular scientific questions, especially those of a comparative nature, thereby leading to robust conclusions of theoretical import or practical use in management or conservation.

Instream structures such as dams and weirs create artificial barriers to the passage of riverine fish, fragmenting their communities and contributing to global declines in freshwater fish biodiversity. Preventing further declines requires the remediation of barriers to restore fish passage, but analysis of fragmented fish communities is necessary to prioritize locations and fish taxa for remediation. Additionally, the potential for high flow events to facilitate barrier drown-out and reduce fragmentation remains unresolved. We used a meta-regression analysis to investigate the severity of fish fragmentation in relation to barrier features, fish traits, and river flows, quantifying fragmentation with a novel log response ratio metric reflecting the asymmetry of fish populations around barriers. We discovered that high barriers, barriers which separate different sized habitats, and clusters of sequential barriers cause more severe fragmentation and should be prioritized for remediation. Currently, barrier remediation is focused on improving passage for mobile fishes, but taxa which migrate short distances and have poor swimming performance were most fragmented, suggesting efforts are warranted to improve passage for less vagile fishes. We found evidence that fragmentation was reduced by large river flows which spill onto the floodplain and provide additional connectivity around barriers, particularly in highly regulated sections of stream with many sequential barriers. The findings of this study can be applied to improve the management of fish passage in rivers, an area of increasing relevance with the worsening discontinuity of rivers due to climate change and the continued construction of barriers.

Relationships between biodiversity and ecosystem functioning (BEF) are typically investigated separately in different ecosystem types, often neglecting connections across ecosystem boundaries. Here, we examined the cross-boundary relationships between terrestrial and aquatic biodiversity and terrestrial and aquatic ecosystem function (here productivity in terms of biomass). We collected a dataset from 100 Finnish boreal lakes for phytoplankton and zooplankton, and for trees and understory plants in the surrounding forest ecosystems. We explored the connections among climatic, catchment, and local environmental factors, and terrestrial and aquatic biodiversity and productivity using structural equation modeling (SEM). The results indicated cross-boundary connections between the two realms. Terrestrial biodiversity was associated with terrestrial productivity and connected to lake water chemistry directly and indirectly through terrestrial productivity. Water chemistry in turn was linked to aquatic biodiversity and productivity. Within both realms, biodiversity was positively associated with ecosystem productivity. The effects of biodiversity per se were weaker in the aquatic realm, in which nutrient availability was the strongest determinant of productivity. Our findings underscore the importance of exploring cross-ecosystem coupling, as the impacts of several global change drivers, such as climate and land-use change or eutrophication, extend beyond individual realms to transcend ecosystem boundaries. In particular, the combined effects of warming, eutrophication, and increasing terrestrial productivity are likely to increase the import of allochthonous nutrients to boreal lake ecosystems, resulting in enhanced primary productivity therein. As freshwater ecosystems integrate the effects of direct and indirect changes in their catchments, they serve as ideal settings for investigating cross-ecosystem coupling and act as valuable sentinels of climate and other global changes.

Ecological communities frequently exhibit remarkable taxonomic and trait diversity, and this diversity is consistently shown to regulate ecosystem function and resilience. However, ecologists lack a synthetic theory for how this diversity is maintained when species compete for limited resources, hampering our ability to project the future of biodiversity under climate change. Water-limited plant communities are an ideal system in which to study these questions given (1) the diversity of hydraulic traits they exhibit, (2) the importance of this diversity for ecosystem productivity and drought resilience, and (3) forecast changes to precipitation and evapotranspiration under climate change. We developed an analytically tractable model of water and light competition in age-structured perennial plant communities and demonstrated that high diversity is maintained through phenological division of the time between storms. We modeled a system where water arrives in the form of intermittent storms, between which plants consume the limited pool of soil water until it becomes dry enough that they must physiologically shut down to avoid embolism. Competition occurs because individuals, by consuming the shared water pool, cause their competitors to shut down earlier, harming their long-term growth and reproduction. When total precipitation is low, plants in the model compete only for water. However, increases in precipitation can cause the canopy to close and individuals to begin competing for light. Variation among species in the minimum soil water content at which they can sustain growth without embolizing leads to emergent phenological variation, as species will shut down at varying points between storm events. When this variation is paired with a trade-off such that species that shut down early are compensated by faster biomass accumulation, higher fecundity, or lower mortality, there is no limit to the number that can coexist. These results are robust to variation in both total precipitation and the time between storms. The model therefore offers a plausible explanation for how hydraulic trait diversity is maintained in a wide array of natural systems. More broadly, this work illustrates how the phenological division of an apparently singular resource can emerge because of common trade-offs and ultimately foster high taxonomic and trait diversity.

Whether, and which, individuals migrate or not is rapidly changing in many populations. Exactly how and why environmental change alters migration propensity is not well understood. We constructed density-dependent structured population models to explore conditions for the coexistence of migrants and residents. Our theoretical models were motivated by empirical data identified via a systematic literature review. We find that the equilibrium density in the season with the strongest density dependence of a strategy predicts whether the strategy will become dominant within the population. This equilibrium density represents strategy fitness in a seasonal environment and can be used to examine selection on migratory behavior. Whether partial migration can be maintained within a population depends on where in the annual cycle density dependence operates. Diversified bet-hedging, where parents produce a mix of migrants and residents, also maintains partial migration. Our study disentangles density-dependent and density-independent rates in a population with seasonal structure, potentially providing routes to explain the rapid change in migration strategies observed in many populations.

Biodiversity underpins the functional integrity of ecosystems. At present, our understanding of the relationship between biodiversity and ecosystem functioning (BEF) is essentially based on manipulative experiments. Compelling data at large spatial scales are scarce, especially for river networks. BEF patterns across landscapes are complex because they unfold in the context of environmental gradients and compositional turnover of natural communities. Leaf litter decomposition, a pivotal ecosystem process in streams, is no exception to this context dependency. The dendritic structure of river networks plus the unidirectional water flow shape both environmental conditions and the distribution of leaf resources and consumers. However, it is difficult to predict how spatial gradients of resource and consumer composition can overlap across a river network, and thus govern spatial patterns of decomposition. Here, we investigated the capacity of macroinvertebrate biodiversity to control decomposition rates of heterogeneous leaf resources at the river-network scale. We deployed five litterbags containing either one of four single leaf species or a mixture of all species at 51 sites across the Thur River network (Switzerland). We measured litter decomposition rates, variation of decomposition among leaf resources, and the effect of leaf litter diversity on decomposition. We found that decomposition rates decreased from headwaters to downstream reaches mainly due to the parallel decrease in the abundance of key shredder taxa (namely, Amphinemura, Nemoura, Leuctra, Habroleptoides, and Stenophylacini). Macroinvertebrate diversity had a minor, negative effect on decomposition rates. However, high functional macroinvertebrate diversity at the reach scale reduced the variation of decomposition among leaf resources, thus alleviating nutritional constraints exerted by nutrient-poor leaf resources. Furthermore, litter mixtures were preferably decomposed by communities with low evenness and dominated by a few taxa. These findings point to a critical role of macroinvertebrates in controlling litter decomposition at the network scale beyond environmental effects. While shredder abundance and community composition are key to determining decomposition rates across the river network, functional diversity is important in decreasing the variation of decomposition rates among leaf resources. Our results stress the importance of biodiversity controlling ecosystem functioning not only at the local but also at the river network scale.

Beta diversity—the variation among community compositions in a region—is a fundamental measure of biodiversity. Most classic measures have posited that beta diversity is maximized when each community has a distinct, nonoverlapping set of species. However, this assumption overlooks the ecological significance of species interactions and non-additivity in ecological systems, where the function and behavior of species depend on other species in a community. Here, we introduce a geometric approach to measure beta diversity as the hypervolume of the geometric embedding of a metacommunity. Besides considering compositional distinctiveness as in classic metrics, this geometric measure explicitly incorporates species associations and captures the idea that adding a unique, species-rich community to a metacommunity increases beta diversity. We show that our geometric measure is closely linked to and naturally extends previous information- and variation-based measures. Additionally, we provide a unifying geometric framework for widely adopted extensions of beta diversity. Applying our geometric measures to empirical data, we address two long-standing questions in beta diversity research—the latitudinal pattern of beta diversity and the effect of sampling effort—and present novel ecological insights that were previously obscured by the limitations of classic approaches. In sum, our geometric approach offers a new and complementary perspective on beta diversity, is immediately applicable to existing data, and holds promise for advancing our understanding of the complex relationships between species composition, ecosystem functioning, and stability.