Biology subjects

McCann, K. S.

Publications and source records attributed to McCann, K. S..

9 recordsLinked to original sources

bioRxiv2025

Fish spawning events stimulate trophic hotspots across freshwater food webs

1.0Mass reproductive events, where large numbers of organisms aggregate for synchronous reproduction, are often captivating and ecologically significant, boosting offspring survival and reducing time spent searching for mates. However, mass reproduction can also instigate cryptic but consequential responses across entire food webs. Reproductive materials are abundant and accessible resources that can attract mobile consumers from up to thousands of kilometers away. Yet, their consumption, especially in aquatic systems, is difficult to detect and rarely characterized. Here, we combine molecular techniques with acoustic telemetry, literature review, and extensive natural history observations to investigate the food web consequences of synchronized reproduction in freshwater fishes. First, we demonstrate that a common but underappreciated fish species, white sucker, creates a resource pulse used ubiquitously by consumers, from local invertebrates and fishes to mobile predatory fishes, birds, and terrestrial mammals. Spawning white sucker create trophic hotspots that attract consumers across trophic levels and ecosystems to feed on eggs, spawning adults, and aggregated egg predators. Then we show that egg provisioning and predation is widespread among north-temperate freshwater fish species, highlighting that resource pulses instigated by mass reproduction may play a critical but underappreciated role in freshwater and terrestrial ecosystems.

ecology↗

bioRxiv2023

Can higher-order interactions resolve the species coexistence paradox?

Most ecological models are based on the assumption that species interact in pairs. Emerging in diverse communities, however, are higher-order interactions, in which two or more species jointly impact the growth of a third species. A pitfall of the pairwise approach is that it misses the higher-order interactions potentially responsible for maintaining diversity in nature. Here, we explore how well higher-order interactions enable coexistence when pairwise interactions are insufficient to do so. Specifically, we explore the stability properties of systems where higher-order interactions guarantee that a specified set of abundances are a feasible equilibrium of the dynamics. Even these higher-order interactions do not necessarily produce robust coexistence. We find that facilitative higher-order interactions that counter pairwise competitive interactions are less likely to generate stable equilibria than competitive interactions countering pairwise facilitation. In both cases the system is more likely to be stable when the pairwise interactions are weak, and when the equilibrium abundances are near those produced by the pairwise interactions. Last, we show that correlations between the pairwise and higher-order interactions permit robust coexistence in diverse systems. Our work reveals the challenges in generating stable coexistence through higher-order interactions, but also uncovers higher-order interaction patterns that can enable diversity.

ecology↗

bioRxiv2022

Towards a multi-stressor theory for coral reefs in a changing world

Coral reefs are facing a constant barrage of human impacts, including eutrophication, overharvesting and climate change. While the local effects of overharvesting have been well-studied, regional nutrient loading from anthropogenic activities on land and global climate change-induced disturbances are increasing in magnitude and necessitating cross-scale multi-stressor approaches for coral reef ecology. Here, we expand on longstanding theory to develop an integrated multi-stressor framework for coral reefs. We show that: i) the geometry of a simple, empirically-motivated model suggests nutrients and harvesting can operate similarly, and synergistically, in driving shifts from coral- to algae-dominated reefs, resulting in clear context-dependent management implications; and ii) this same geometry suggests climate-driven coral mortality can drive the presence of long transients and climate-driven alternate states, even in moderately-impacted ecosystems. Reefs seemingly in a "safe space" based on individual stressors may in fact be much more susceptible to increasingly frequent storms and bleaching events in multi-stressor conditions. By integrating these findings with general ecological and theoretical concepts, we suggest that responses in benthic composition may act as "signatures of change" to multi-stressors, allowing us to develop a predictive and generalizable multi-stressor framework for coral reefs under global change. In line with this theory, we detail empirical evidence from Barbados of historical changes in reef composition and multi-stressor impacts within our framework. By bridging coral reef ecology and general ecological concepts, we can better understand ecosystem functioning and resilience in these important yet highly threatened systems. Manuscript HighlightsO_LITheoretical understanding of synergistic multi-stressor impacts on coral reefs C_LIO_LIUnexpected climate-driven alternate states, related to long transients C_LIO_LITheoretical framework predicts "signatures of change" based on dominant stressor C_LI

ecology↗

bioRxiv2022

Slower organisms exhibit sudden population disappearances in a reddened world

Nature is replete with variation in the body sizes, reproductive output, and generation times of species that produce life history responses known to vary from small and fast to large and slow. Although researchers recognize that life history speed likely dictates fundamental processes in consumer-resource interactions like productivity and stability, theoretical work remains incomplete in this critical area. Here, we examine the role of life history speed on consumer-resource interactions by using a well used mathematical approach that manipulates the speed of the consumers growth rate in a consumer-resource interaction. Importantly, this approach holds the isocline geometry intact allowing us to assess the impacts of altered life history speed on stability (coefficient of variation, CV) without changing the underlying qualitative dynamics. Although slowing life history can be initially stabilizing, we find that in stochastic settings slowing ultimately drives highly destabilizing population disappearances, especially under reddened noise. Our results suggest that human-driven reddening of noise may decrease species stability because the autocorrelation of red noise enlarges the period and magnitude of perturbations, overwhelming a species natural compensatory responses via a ratchet-like effect. This ratchet-like effect then pushes species population dynamics far away from equilibria that can lead to precipitous local extinction.

ecology↗

bioRxiv2021

Increased brain growth in escaped rainbow trout

Recent examples of rapid brain size plasticity in response to novel laboratory environments suggest that fish brain size is a flexible trait, allowing growth or shrinkage of brain tissue based on short term needs. Nevertheless, it remains to be seen if plasticity of fish brain size is relevant to natural environmental conditions. Here, using rainbow trout escaped from a farming operation as a natural experiment, we demonstrate that adult fish brain size can change rapidly in response to life in a natural lake environment. Specifically, escaped trout had on average 15% heavier brains relative to body size than captive trout after living for about 7 months in the lake. Because relative brain size of most escaped trout fell above the range of variation seen within the captive trout population, we conclude that increased brain size was achieved by plasticity after escape. Brain morphology analysis showed that the most anterior regions (olfactory bulbs and rest of telencephalon) contributed most to the increase in overall brain size in escaped trout. Relative size of the heart ventricle, another organ which can be subject to plastic changes under variable environmental conditions in fish, did not differ between escaped and captive trout. Massive and selective brain growth under the changed environmental conditions associated with escape from holding pens highlighted the plastic potential of fish brain size and suggests that a shift to increased complexity of life in the wild setting of a lake imposed greatly increased cognitive requirements on escaped trout.

zoology↗

bioRxiv2020

Spatial fingerprinting: horizontal fusion of multi-dimensional bio-tracers as solution to global food provenance problems

Building the capacity of efficiently determining the provenance of food products represents a crucial step towards the sustainability of the global food system. Whether it is for enforcing existing egislation or providing reliable information to consumers, technologies to verify geographical origin of food are being actively developed. Biological tracers (bio-tracers) such as DNA and stable isotopes have recently demonstrated their potential for determining provenance. Here we show that the data fusion of bio-tracers is a very powerful technique for geographical provenance discrimination. Based on 90 individuals of Sockeye salmon that originate from 3 different areas for which we measured 17 bio-tracers, we demonstrate that increasing the combined bio-tracers results in stronger the discriminatory power. The generality of our results are mathematically demonstrated under simplifying assumptions and numerically confirmed in our case study using three commonly used supervised learning techniques.

ecology↗

bioRxiv2019

Coherent whole food web responses to outbreaking spruce budworm

The world is astoundingly variable, and individuals to whole communities must respond to variability to survive. One example of natures variability is the massive fluctuations in spruce budworm (Choristoneura fumiferana Clemens, Lepidoptera: Tortricidae) populations that occur over 35 years. We examined how the parasitoid community altered its parasitism of budworm and other caterpillar species in response to these fluctuations. Budworm and other caterpillar species were sampled from balsam fir in three plots for 14 years in Atlantic Canada, and then reared to identify any emerging parasitoids. We found that the parasitoid community showed a simple linear, indiscriminate response (i.e., no preference, where densities purely dictated parasitism rates) to changes in budworm densities relative to other caterpillar species on balsam fir. We also observed strong changes in topology and distributions of interaction strengths between the parasitoids, budworm and other caterpillar species as budworm densities fluctuated. Our study contributes to the suggestion that hardwood trees are a critical part of the budworm-parasitoid food web, where parasitoids attack other caterpillar species on hardwood trees when budworm populations are low. Taken together, our study shows that a parasitoid community collectively alters species interactions in response to variable budworm densities, fundamentally shifting food web pathways.

ecology↗

bioRxiv2019

Thermal preferences drive behavioural responses but not biomass responses of predatory fishes to lake morphometry

Top predators responses to environmental conditions shape food web architecture and influence ecosystem structure and stability. Yet the impacts of fundamental properties like ecosystem size and morphometry on top predators behaviour are poorly understood. We examined how lake morphometry impacts the behaviour (inferred by depth use) of three key fish top predators--the cold-adapted lake trout, the cool-adapted walleye, and the warm-adapted smallmouth bass-- which can each strongly impact local food web structure. We used catch-per-unit-effort data from nearly 500 boreal lakes of Ontario, Canada to evaluate the role of thermal preference in dictating mean depth of capture and biomass index in response to lake morphometry. We found evidence that thermal preferences influence how species depth use and biomass changed with lake size, proportion of littoral area, and maximum lake depth, although we found no relationship with lake shape. However, found no strong evidence that lake morphology influences these species biomasses, despite theory that predicts such a relationship. Our results suggest that some aspects of lake morphometry can alter habitat accessibility and productivity in ways that influence the behaviour and biomass of these top predator species depending on their thermal preferences. Our results have implications for how lake food webs expand and contract with lake morphometry and other key abiotic factors. We argue that several key abiotic factors likely drive top predator depth use in ways that may shape local food web structure and play an important role in determining the ultimate fate of ecosystems with environmental change.

ecology↗

bioRxiv2018

Multiple species drive flexible lake food webs with warming

Climate change is rewiring the food webs that determine the fate of diverse ecosystems. Mobile generalist consumers are responding to climate change by rapidly shifting their behaviour and foraging, driving food webs to flex. Although these responsive generalists form a key stabilizing module in food web structure, the extent to which they are present throughout whole food webs is largely unknown. Here, we show that multiple species comprising key trophic roles drive flexible lake food webs with warming. By examining lakes that span a 7{degrees}C air temperature gradient, we found significant reductions in nearshore derived carbon and nearshore habitat use with increased temperature in three of four fish species. We also found evidence that the response of lake trout to increased temperatures may reduce their biomass and cascade to release their preferred prey, the pelagic forage fish cisco. Our results suggest that climate warming will shift lake food webs toward increased reliance on offshore habitats and resources. We argue that species across trophic levels broadly couple lake macrohabitats, suggesting that potentially stabilizing responsive consumers are present throughout food webs. However, climate change appears to limit their ability to responsively forage, critically undermining a repeated stabilizing mechanism in food webs.

ecology↗