An official website of the United States government
The determinants of food chain length (FCL), a crucial aspect of biodiversity due to its effects on ecosystem functioning, have long been debated. Previous studies proposed resource availability, disturbance, and ecosystem size as environmental drivers. However, studies using stable isotope approaches have shown inconsistent results, indicating missing links between environmental drivers and FCL. Here, we hypothesized that species richness and motifs (i.e. three‐species subgraphs) modulated environmental effects on FCL. Combining empirical food webs with ourN‐species food web model, we found that FCL disproportionately changed at low species richness, with saturation at high species richness. This functional response was essential to the interdependent effects of disturbance and ecosystem size in our model. Disturbance more strongly regulated FCL in smaller ecosystems, where species richness was low. Similarly, increasing ecosystem size enhanced FCL under strong, but not weak, disturbance regimes. Our study suggests that internal food web structure should deepen our understanding of how FCL changes over environments.
more »
« less
Ecosystem size and complexity as extrinsic drivers of food chain length in branching ecosystems
Abstract Understanding the drivers of food chain length in natural communities has intrigued ecologists since Elton publicized “food cycles” in the early 20th century. Proposed drivers of food chain length have included productivity, disturbance regime, ecosystem size, and trophic omnivory. However, current theories have largely assumed simple, two‐dimensional habitat architectures and may not be adequate to predict food chain length in ecosystems with a complex, branching structure. Here, we develop a spatially explicit theoretical model that provides an integrated framework for understanding variation in food chain length in branching networks. We show independent, positive influences of ecosystem size and complexity (as indicated by branching properties) on food chain length. However, the effects of ecosystem size and complexity were contingent upon other factors, appearing more clearly in high‐disturbance and high‐productivity regimes. Our results suggest that ecosystem complexity is an important yet overlooked driver of food chain length that may increase the resilience to anthropogenic environmental changes.
more »
« less
- Award ID(s):
- 2015634
- PAR ID:
- 10446941
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecosphere
- Volume:
- 14
- Issue:
- 8
- ISSN:
- 2150-8925
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
A prevailing paradigm suggests that species richness increases with area in a decelerating way. This ubiquitous power law scaling, the species–area relationship, has formed the foundation of many conservation strategies. In spatially complex ecosystems, however, the area may not be the sole dimension to scale biodiversity patterns because the scale-invariant complexity of fractal ecosystem structure may drive ecological dynamics in space. Here, we use theory and analysis of extensive fish community data from two distinct geographic regions to show that riverine biodiversity follows a robust scaling law along the two orthogonal dimensions of ecosystem size and complexity (i.e., the dual scaling law). In river networks, the recurrent merging of various tributaries forms fractal branching systems, where the prevalence of branching (ecosystem complexity) represents a macroscale control of the ecosystem’s habitat heterogeneity. In the meantime, ecosystem size dictates metacommunity size and total habitat diversity, two factors regulating biodiversity in nature. Our theory predicted that, regardless of simulated species’ traits, larger and more branched “complex” networks support greater species richness due to increased space and environmental heterogeneity. The relationships were linear on logarithmic axes, indicating power law scaling by ecosystem size and complexity. In support of this theoretical prediction, the power laws have consistently emerged in riverine fish communities across the study regions (Hokkaido Island in Japan and the midwestern United States) despite hosting different fauna with distinct evolutionary histories. The emergence of dual scaling law may be a pervasive property of branching networks with important implications for biodiversity conservation.more » « less
-
Abstract Cross-ecosystem subsidies influence the structure and dynamics of recipient ecosystems and can be sensitive to disturbance. Primary production exported from marine to shoreline ecosystems is among the largest known cross-ecosystem subsidies. However, the spatial scales at which this important connection is manifested are largely unquantified. We used local and regional observations of nearshore kelp canopy biomass and beach kelp wrack inputs to evaluate the scales at which connectivity between kelp forests and beaches is maximized. Regardless of the spatial and temporal scales considered, connectivity was highly local (<10 km) and strongest in winter. Kelp canopy biomass was the primary driver of wrack subsidies, but recipient ecosystem attributes, particularly beach width and orientation, were also important. These drivers of connectivity highlight that disturbance to either ecosystem will have large implications for beach ecosystem productivity. Spatial connectivity can regulate recovery from disturbances such that ecosystem connections must be considered in conservation efforts.more » « less
-
Abstract Understanding variation in food web structure over large spatial scales is an emerging research agenda in food web ecology. The density of predator–prey links in a food web (i.e., connectance) is a key measure of network complexity that describes the mean proportional dietary breadth of species within a food web. Connectance is a critical component of food web robustness to species loss: food webs with lower connectance have been shown to be more susceptible to secondary extinctions. Identifying geographic variation in food web connectance and its drivers may provide insight into community robustness to species loss. We investigated the food web connectance of ground-dwelling tropical forest mammal communities in multiple biogeographic regions to test for differences among regions in food web connectance and to test three potential drivers: primary productivity, contemporary anthropogenic pressure, and variation in mammal body mass distributions reflective of historical extinctions. Mammal communities from fifteen protected forests throughout the Neo-, Afro-, and Asian tropics were identified from systematic camera trap arrays. Predator–prey interaction data were collected from published literature, and we calculated connectance for each community as the number of observed predator–prey links relative to the number of possible predator–prey links. We used generalized linear models to test for differences among regions and to identify the site level characteristics that best predicted connectance. We found that mammal food web connectance varied significantly among continents and that body size range was the only significant predictor. More possible predator–prey links were observed in communities with smaller ranges in body size and therefore sites with smaller body size ranges had higher mean proportional dietary breadth. Specifically, mammal communities in the Neotropics and in Madagascar had significantly higher connectance than mammal communities in Africa. This geographic variation in contemporary mammalian food web structure may be the product of historical extinctions in the Late Quaternary, which led to greater losses of large-bodied species in the Neotropics and Madagascar thus contributing to higher average proportional dietary breadth among the remaining smaller bodied species in these regions.more » « less
-
Abstract Coastal systems experience frequent disturbance and multiple environmental stressors over short spatial and temporal scales. Investigating functional traits in coastal systems has the potential to inform how variation in disturbance frequency and environmental variables influence differences in trait‐based community composition and ecosystem function. Our goals were to (1) quantify trait‐based communities on two barrier islands divergent in topography and long‐term disturbance response and (2) determine relationships between community trait‐based composition and ecosystem productivity. We hypothesized that locations documented with high disturbance would have habitats with similar environmental conditions and trait‐based communities, with the opposite relationship in low‐disturbance locations. Furthermore, we expected higher productivity and lower site‐to‐site variation with low disturbance. Functional traits, biomass, and environmental metrics (soil salinity, elevation, and distance to shoreline) were collected and analyzed for two habitat types (dune and swale) on two Virginia barrier islands. Our results show that trait‐based community composition differed among habitat types and was related to disturbance. Habitats exhibited more similarity on the high‐disturbance island in both trait‐based composition and environmental variables. Conversely, the low‐disturbance island habitats were more dissimilar. We found the habitat with the lowest disturbance had the highest ecosystem productivity and had trait‐based communities indicative of highly competitive environments, while the high‐disturbance trait‐based communities were influenced by traits that indicate rapid recovery and growth. Site‐to‐site variation was similar in all dune habitats but differed among inter‐island swale habitats that varied in disturbance. These results highlight the importance of incorporating trait‐based analyses when approaching questions about community structure and ecosystem productivity in disturbance‐mediated habitats, such as coastal systems.more » « less
