An official website of the United States government
Abstract How strongly predators and prey interact is both notoriously context dependent and difficult to measure. Yet across taxa, interaction strength is strongly related to predator size, prey size and prey density, suggesting that general cross‐taxonomic relationships could be used to predict how strongly individual species interact.Here, we ask how accurately do general size‐scaling relationships predict variation in interaction strength between specific species that vary in size and density across space and time?To address this question, we quantified the size and density dependence of the functional response of the California spiny lobsterPanulirus interruptus, foraging on a key ecosystem engineer, the purple sea urchinStrongylocentrotus purpuratus, in experimental mesocosms. Based on these results, we then estimated variation in lobster–urchin interaction strength across five sites and 9 years of observational data. Finally, we compared our experimental estimates to predictions based on general size‐scaling relationships from the literature.Our results reveal that predator and prey body size has the greatest effect on interaction strength when prey abundance is high. Due to consistently high urchin densities in the field, our simulations suggest that body size—relative to density—accounted for up to 87% of the spatio‐temporal variation in interaction strength. However, general size‐scaling relationships failed to predict the magnitude of interactions between lobster and urchin; even the best prediction from the literature was, on average, an order of magnitude (+18.7×) different than our experimental predictions.Harvest and climate change are driving reductions in the average body size of many marine species. Anticipating how reductions in body size will alter species interactions is critical to managing marine systems in an ecosystem context. Our results highlight the extent to which differences in size‐frequency distributions can drive dramatic variation in the strength of interactions across narrow spatial and temporal scales. Furthermore, our work suggests that species‐specific estimates for the scaling of interaction strength with body size, rather than general size‐scaling relationships, are necessary to quantitatively predict how reductions in body size will alter interaction strengths.
more »
« less
Linear scaling between microbial predator and prey densities in the global ocean
Abstract It has been proposed that microbial predator and prey densities are related through sublinear power laws. We revisited previously published biomass and abundance data and fitted Power‐law Biomass Scaling Relationships (PBSRs) between marine microzooplankton predators (Z) and phytoplankton prey (P), and marine viral predators (V) and bacterial prey (B). We analysed them assuming an error structure given by Type II regression models which, in contrast to the conventional Type I regression model, accounts for errors in both the independent and the dependent variables. We found that the data support linear relationships, in contrast to the sublinear relationships reported by previous authors. The scaling exponent yields an expected value of 1 with some spread in different datasets that was well‐described with a Gaussian distribution. Our results suggest that the ratiosZ/P, andV/Bare on average invariant, in contrast to the hypothesis that they systematically decrease with increasingPand B, respectively, as previously thought.
more »
« less
- Award ID(s):
- 2023680
- PAR ID:
- 10381266
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Environmental Microbiology
- Volume:
- 25
- Issue:
- 2
- ISSN:
- 1462-2912
- Format(s):
- Medium: X Size: p. 306-314
- Size(s):
- p. 306-314
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Many critical drivers of ecological systems exhibit regular scaling relationships, yet the underlying mechanisms explaining these relationships are often unknown. Trophic interaction strengths, which underpin ecosystem stability and dynamics, are no exception, exhibiting statistical scaling relationships with predator and prey traits that lack causal, evolutionary explanations. Here we propose two universal rules to explain the scaling of trophic interaction strengths through the relationship between a predator’s feeding rate and its prey’s density --- the so-called predator functional response. First, functional responses must allow predators to meet their energetic demands when prey are rare. Second, functional responses should approach their maxima near the highest prey densities that predators experience. We show that independently parameterized mathematical equations derived from these two rules predict functional response parameters across over 2,100 functional response experiments. The rules further predict consistent patterns of feeding rate saturation among predators, a slow-fast continuum among functional response parameters, and the allometric scaling of those parameters. The two rules thereby offer a potential ultimate explanation for the determinants of trophic interaction strengths and their scaling, revealing the importance of ecologically realized constraints to the complex, adaptive nature of functional response evolution.more » « less
-
Enrico Pirotta (Ed.)Abstract AimUnderstanding the distribution of marine organisms is essential for effective management of highly mobile marine predators that face a variety of anthropogenic threats. Recent work has largely focused on modelling the distribution and abundance of marine mammals in relation to a suite of environmental variables. However, biotic interactions can largely drive distributions of these predators. We aim to identify how biotic and abiotic variables influence the distribution and abundance of a particular marine predator, the bottlenose dolphin (Tursiops truncatus), using multiple modelling approaches and conducting an extensive literature review. LocationWestern North Atlantic continental shelf. MethodsWe combined widespread marine mammal and fish and invertebrate surveys in an ensemble modelling approach to assess the relative importance and capacity of the environment and other marine species to predict the distribution of both coastal and offshore bottlenose dolphin ecotypes. We corroborate the modelled results with a systematic literature review on the prey of dolphins throughout the region to help explain patterns driven by prey availability, as well as reveal new ones that may not necessarily be a predator–prey relationship. ResultsWe find that coastal bottlenose dolphin distributions are associated with one family of fishes, the Sciaenidae, or drum family, and predictions slightly improve when using only fish versus only environmental variables. The literature review suggests that this tight coupling is likely a predator–prey relationship. Comparatively, offshore dolphin distributions are more strongly related to environmental variables, and predictions are better for environmental‐only models. As revealed by the literature review, this may be due to a mismatch between the animals caught in the fish and invertebrate surveys and the predominant prey of offshore dolphins, notably squid. Main ConclusionsIncorporating prey species into distribution models, especially for coastal bottlenose dolphins, can help inform ecological relationships and predict marine predator distributions.more » « less
-
Dam, Hans G. (Ed.)Recent research has revealed the diversity and biomass of life across ecosystems, but how that biomass is distributed across body sizes of all living things remains unclear. We compile the present-day global body size-biomass spectra for the terrestrial, marine, and subterranean realms. To achieve this compilation, we pair existing and updated biomass estimates with previously uncatalogued body size ranges across all free-living biological groups. These data show that many biological groups share similar ranges of body sizes, and no single group dominates size ranges where cumulative biomass is highest. We then propagate biomass and size uncertainties and provide statistical descriptions of body size-biomass spectra across and within major habitat realms. Power laws show exponentially decreasing abundance (exponent -0.9±0.02 S.D.,R2= 0.97) and nearly equal biomass (exponent 0.09±0.01,R2= 0.56) across log size bins, which resemble previous aquatic size spectra results but with greater organismal inclusivity and global coverage. In contrast, a bimodal Gaussian mixture model describes the biomass pattern better (R2= 0.86) and suggests small (~10−15g) and large (~107g) organisms outweigh other sizes by one order magnitude (15 and 65 Gt versus ~1 Gt per log size). The results suggest that the global body size-biomass relationships is bimodal, but substantial one-to-two orders-of-magnitude uncertainty mean that additional data will be needed to clarify whether global-scale universal constraints or local forces shape these patterns.more » « less
-
Abstract Euphausiids are important prey for many marine organisms and often occur in patchy aggregations. Euphausiid predators, such as blue whales, may become concentrated in the vicinity of these aggregations. We investigated an area called Nine Mile Bank (NMB) near San Diego, California, defined by an area of steep bathymetry, to determine whether the frequent whale sightings in that locality can be explained by the distribution of euphausiids across the bank and by the vertical distribution of euphausiids in the water column.Thysanoessa spinifera, the strongly preferred blue whale prey euphausiid in this area, was consistently more abundant on the bank or inshore of it than offshore. In contrast,Euphausia pacifica,a minor blue whale prey item, was much more abundant and distributed across the study region. Adults of both species were concentrated in a stratum corresponding to the feeding depth of blue whales. Other euphausiids that form a negligible part of the blue whale diet also showed no association with NMB. Both blue whales and their primary prey speciesThysanoessa spiniferawere more abundant on or inshore of the bank than offshore, suggesting that the bank may serve as an offshore limit of high prey abundance that helps to concentrate blue whales.more » « less
