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1. Extreme site fidelity as an optimal strategy in an unpredictable and homogeneous environment

   https://doi.org/10.1111/1365-2435.13390  

   Gerber, Brian D. ; Hooten, Mevin B. ; Peck, Christopher P. ; Rice, Mindy B. ; Gammonley, James H. ; Apa, Anthony D. ; Davis, Amy J. ; Lemaître, ed., Jean‐François ( July 2019 , Functional Ecology)

   Animal site fidelity structures space use, population demography and ultimately gene flow. Understanding the adaptive selection for site fidelity patterns provides a mechanistic understanding to both spatial and population processes. This can be achieved by linking space use with environmental variability (spatial and temporal) and demographic parameters. However, rarely is the environmental context that drives the selection for site fidelity behaviour fully considered.

   We use ecological theory to understand whether the spatial and temporal variability in breeding site quality can explain the site fidelity behaviour and demographic patterns of Gunnison sage‐grouse (Centrocercus minimus). We examined female site fidelity patterns across multiple spatial scales: proximity of consecutive year nest locations, space‐use overlap within and across the breeding and brooding seasons, and fidelity to a breeding patch. We also examined the spatial and temporal variability in nest, chick, juvenile and adult survival.

   We found Gunnison sage‐grouse to be site faithful to their breeding patch, area of use within the patch and generally where they nest, suggesting an “Always Stay” site fidelity strategy. This is an optimal evolutionary strategy when site quality is unpredictable. Further, we found limited spatial variability in survival within age groups, suggesting little demographic benefit to moving among patches. We suggest Gunnison sage‐grouse site fidelity is driven by the unpredictability of predation in a relatively homogeneous environment, the lack of benefits and likely costs to moving across landscape patches and leaving known lek and breeding/brooding areas.

   Space use and demography are commonly studied separately. More so, site fidelity patterns are rarely framed in the context of ecological theory, beyond questions related to the win‐stay:lose‐switch rule. To move beyond describing patterns and understand the adaptive selection driving species movements and their demographic consequences require integrating movement, demography and environmental variability in a synthetic framework.

   Site fidelity theory provides a coherent framework to simultaneously investigate the spatial and population ecology of animal populations. Using it to frame ecological questions will lead to a more mechanistic understanding of animal movement, spatial population structuring and meta‐population dynamics.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Negative frequency‐dependent foraging behaviour in a generalist herbivore ( Alces alces ) and its stabilizing influence on food web dynamics

   https://doi.org/10.1111/1365-2656.13031  

   Hoy, Sarah R. ; Vucetich, John A. ; Liu, Rongsong ; DeAngelis, Don L. ; Peterson, Rolf O. ; Vucetich, Leah M. ; Henderson, John J. ; Street, ed., Garrett ( July 2019 , Journal of Animal Ecology)

   Resource selection is widely appreciated to be context‐dependent and shaped by both biological and abiotic factors. However, few studies have empirically assessed the extent to which selective foraging behaviour is dynamic and varies in response to environmental conditions for free‐ranging animal populations.

   Here, we assessed the extent that forage selection fluctuated in response to different environmental conditions for a free‐ranging herbivore, moose (Alces alces), in Isle Royale National Park, over a 10‐year period. More precisely, we assessed how moose selection for coniferous versus deciduous forage in winter varied between geographic regions and in relation to (a) the relative frequency of forage types in the environment (e.g. frequency‐dependent foraging behaviour), (b) moose abundance, (c) predation rate (by grey wolves) and (d) snow depth. These factors are potentially important for their influence on the energetics of foraging. We also built a series of food‐chain models to assess the influence of dynamic foraging strategies on the stability of food webs.

   Our analysis indicates that moose exhibited negative frequency dependence, by selectively exploiting rare resources. Frequency‐dependent foraging was further mediated by density‐dependent processes, which are likely to be predation, moose abundance or some combination of both. In particular, frequency dependence was weaker in years when predation risk was high (i.e. when the ratio of moose to wolves was relatively low). Selection for conifers was also slightly weaker during deep snow years.

   The food‐chain analysis indicates that the type of frequency‐dependent foraging strategy exhibited by herbivores had important consequences for the stability of ecological communities. In particular, the dynamic foraging strategy that we observed in the empirical analysis (i.e. negative frequency dependence being mediated by density‐dependent processes) was associated with more stable food web dynamics compared to fixed foraging strategies.

   The results of this study indicated that forage selection is a complex ecological process, varying in response to both biological (predation and moose density) and abiotic factors (snow depth) and over relatively small spatial scales (between regions). This study also provides a useful framework for assessing the influence of other aspects of foraging behaviour on the stability of food web dynamics.

    

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3. Drivers of site fidelity in ungulates

   https://doi.org/10.1111/1365-2656.13425  

   Morrison, Thomas A. ; Merkle, Jerod A. ; Hopcraft, J. Grant C. ; Aikens, Ellen O. ; Beck, Jeffrey L. ; Boone, Randall B. ; Courtemanch, Alyson B. ; Dwinnell, Samantha P. ; Fairbanks, W. Sue ; Griffith, Brad ; et al ( February 2021 , Journal of Animal Ecology)

   While the tendency to return to previously visited locations—termed ‘site fidelity’—is common in animals, the cause of this behaviour is not well understood. One hypothesis is that site fidelity is shaped by an animal's environment, such that animals living in landscapes with predictable resources have stronger site fidelity. Site fidelity may also be conditional on the success of animals’ recent visits to that location, and it may become stronger with age as the animal accumulates experience in their landscape. Finally, differences between species, such as the way memory shapes site attractiveness, may interact with environmental drivers to modulate the strength of site fidelity.

   We compared inter‐year site fidelity in 669 individuals across eight ungulate species fitted with GPS collars and occupying a range of environmental conditions in North America and Africa. We used a distance‐based index of site fidelity and tested hypothesized drivers of site fidelity using linear mixed effects models, while accounting for variation in annual range size.

   Mule deerOdocoileus hemionusand mooseAlces alcesexhibited relatively strong site fidelity, while wildebeestConnochaetes taurinusand barren‐ground caribouRangifer tarandus grantihad relatively weak fidelity. Site fidelity was strongest in predictable landscapes where vegetative greening occurred at regular intervals over time (i.e. high temporal contingency). Species differed in their response to spatial heterogeneity in greenness (i.e. spatial constancy). Site fidelity varied seasonally in some species, but remained constant over time in others. Elk employed a ‘win‐stay, lose‐switch’ strategy, in which successful resource tracking in the springtime resulted in strong site fidelity the following spring. Site fidelity did not vary with age in any species tested.

   Our results provide support for the environmental hypothesis, particularly that regularity in vegetative phenology shapes the strength of site fidelity at the inter‐annual scale. Large unexplained differences in site fidelity suggest that other factors, possibly species‐specific differences in attraction to known sites, contribute to variation in the expression of this behaviour.

   Understanding drivers of variation in site fidelity across groups of organisms living in different environments provides important behavioural context for predicting how animals will respond to environmental change.

    

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4. Nutrient Loading and Viral Memory Drive Accumulation of Restriction Modification Systems in Bloom-Forming Cyanobacteria

   https://doi.org/10.1128/mBio.00873-21  

   Papoulis, Spiridon E. ; Wilhelm, Steven W. ; Talmy, David ; Zinser, Erik R. ( June 2021 , mBio)

   Moran, Mary Ann (Ed.)

   ABSTRACT The mechanisms driving cyanobacterial harmful algal blooms (HABs) like those caused by Microcystis aeruginosa remain elusive, but improved defense against viral predation has been implicated for success in eutrophic environments. Our genus-level analyses of 139,023 genomes revealed that HAB-forming cyanobacteria carry vastly more restriction modification systems per genome (RMPG) than nearly all other prokaryotic genera, suggesting that viral defense is a cornerstone of their ecological success. In contrast, picocyanobacteria that numerically dominate nutrient-poor systems have the fewest RMPG within the phylum Cyanobacteria . We used classic resource competition models to explore the hypothesis that nutrient enrichments drive ecological selection for high RMPG due to increased host-phage contact rate. These classic models, agnostic to the mechanism of defense, explain how nutrient loading can select for increased RMPG but, importantly, fail to explain the extreme accumulation of these defense systems. However, extreme accumulation of RMPG can be achieved in a novel “memory” model that accounts for a unique activity of restriction modification systems: the accidental methylation of viral DNA by the methyltransferase. The methylated virus “remembers” the RM defenses of its former host and can evade these defenses if they are present in the next host. This viral memory leads to continual RM system devaluation; RMs accumulate extensively because the benefit of each addition is diminished. Our modeling leads to the hypothesis that nutrient loading and virion methylation drive the extreme accumulation of RMPG in HAB-forming cyanobacteria. Finally, our models suggest that hosts with different RMPG values can coexist when hosts have unique sets of RM systems. IMPORTANCE Harmful algal blooms (HABs), caused by cyanobacteria like Microcystis aeruginosa , are a global threat to water quality and use across the planet. Researchers have agreed that nutrient loading is a major contributor to HAB persistence. While we may understand the environmental conditions that cause HABs, we still struggle in identifying the mechanisms that explain why these organisms have a competitive edge against other, less ecologically hazardous organisms. Our interdisciplinary approach in microbiology, mathematical population modeling, and genomics allows us to use nearly 70 years of research in restriction modification systems to show that HAB-forming cyanobacteria are exceptional in their ability to defend against viruses, and this capacity is intimately tied to nutrient loading. Our hypothesis suggests that defense against viral predation is a fundamental pillar of cyanobacterial ecological strategy and an important contributor to HAB dynamics. 

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5. Dynamic energy landscapes of predators and the implications for modifying prey risk

   https://doi.org/10.1111/1365-2435.14478  

   Papastamatiou, Yannis P. ; Binder, Benjamin M. ; Boswell, Kevin M. ; Malone, Margaret A. ; Heithaus, Michael R. ; Huveneers, Charlie ; Mourier, Johann ; Harborne, Alastair R. ( December 2023 , Functional Ecology)

   Landscapes of fear describe a spatial representation of an animal's perceived risk of predation and the associated foraging costs, while energy landscapes describe the spatial representation of their energetic cost of moving and foraging. Fear landscapes are often dynamic and change based on predator presence and behaviour, and variation in abiotic conditions that modify risk. Energy landscapes are also dynamic and can change across diel, seasonal, and climatic timescales based on variability in temperature, snowfall, wind/current speeds, etc.

   Recently, it was suggested that fear and energy landscapes should be integrated. In this paradigm, the interaction between landscapes relates to prey being forced to use areas of the energy landscape they would avoid if risk were not a factor. However, dynamic energy landscapes experienced by predators must also be considered since they can affect their ability to forage, irrespective of variation in prey behaviour. We propose an additional component to the fear and dynamic energy landscape paradigm that integrates landscapes of both prey and predators, where predator foraging behaviour is modulated by changes in their energyscape.

   Specifically, we integrate the predator's energy landscape into foraging theory that predicts prey patch‐leaving decisions under the threat of predation. We predict that as a predator's energetic cost of foraging increases in a habitat, then the prey's foraging cost of predation and patch quitting harvest rate, will decrease. Prey may also decrease their vigilance in response to increased energetic foraging costs for predators, which will lower giving‐up densities of prey.

   We then provide examples in terrestrial, aerial, and marine ecosystems where we might expect to see these effects. These include birds and sharks which use updrafts that vary based on wind and current speeds, tidal state, or temperature, and terrestrial predators (e.g. wolves) whose landscapes vary seasonally with snow depth or ice cover which may influence their foraging success and even diet selection.

   A predator perspective is critical to considering the combination of these landscapes and their ecological consequences. Dynamic predator energy landscapes could add an additional spatiotemporal component to risk effects, which may cascade through food webs.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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