Living with liver flukes: Does migration matter?

Normandeau, Jacalyn; Kutz, Susan; Hebblewhite, Mark; Merrill, Evelyn H.

doi:10.1016/j.ijppaw.2020.05.002

Cited by 8 publications

(6 citation statements)

References 51 publications

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“…No switching was observed between east to west tactics. (b) Probability of switching to an alternate migratory tactic for resident, eastern, and western migrant elk as a function of the predicted fitness (lambda, λ) derived from the Integrated Population Model, at Ya Ha Tinda, 2002-2019 females were exposed to higher forage quality on the summer range than residents (Hebblewhite & Merrill, 2009) reflected in higher diet quality (Hebblewhite & Merrill, 2009;Normandeau et al, 2020). The reason that winter-range density dependence occurred only for the resident tactic was because higher summer forage quality of migrants affected the probability of pregnancy in the subsequent year and is essential temperate ungulates to regaining body fat and body condition following lactation (Cook et al, 2004(Cook et al, , 2010.…”

Section: Discussionmentioning

confidence: 99%

“…Pregnancy rates of residents declined at high densities, a classic indicator of forage‐limited density dependence (Bonenfant et al, 2009; Stewart et al, 2005). Lower pregnancy rates at higher density provided an incentive to switch migratory tactics because migrant females were exposed to higher forage quality on the summer range than residents (Hebblewhite & Merrill, 2009) reflected in higher diet quality (Hebblewhite & Merrill, 2009; Normandeau et al, 2020). The reason that winter‐range density dependence occurred only for the resident tactic was because higher summer forage quality of migrants affected the probability of pregnancy in the subsequent year and is essential for temperate ungulates to regaining body fat and body condition following lactation (Cook et al, 2004, 2010).…”

Section: Discussionmentioning

confidence: 99%

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Large herbivores in a partially migratory population search for the ideal free home

Martin

Hebblewhite

Merrill

2022

Ecology

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Migration is a tactic used across taxa to access resources in temporally heterogenous landscapes. Populations that migrate can attain higher abundances because such movements allow access to higher quality resources, or reduction in predation risk resulting in increased fitness. However, most migratory species occur in partially migratory populations, a mix of migratory and nonmigratory individuals. It is thought that the portion of migrants in a partial migration population is maintained either through (1) a population-level evolutionary stable state where counteracting density-dependent vital rates act on migrants and residents to balance fitness or (2) conditional migration, where the propensity to migrate is influenced by the individual's state. However, in many respects, migration is also a form of habitat selection and the proportion of migrants and residents may be the result of density-dependent habitat selection. Here, we test whether the theory of Ideal Free Distribution (IFD) can explain the coexistence of different migratory tactics in a partially migratory population. IFD predicts individuals exhibit density-dependent vital rates and select different migratory tactics to maximize individual fitness resulting in equal fitness (λ) between tactics. We tested the predictions of IFD in a partially migratory elk population that declined by 70% with 19 years of demographic data and migratory tactic switching rates from >300 individuals. We found evidence of density dependence for resident pregnancy and adult female survival providing a fitness incentive to switch tactics. Despite differences in vital rates between migratory tactics, mean λ (fitness) was equal. However, as predicted by the IFD, individuals switched tactics toward those of higher fitness. Our analysis reveals that partial migration may be driven by tactic selection that follows the ideal free distribution. These findings reinforce that migration across taxa may be a polymorphic behavior in large herbivores where migratory tactic selection is determined by differential costs and benefits, mediated by density dependence.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Large herbivores in a partially migratory population search for the ideal free home

Martin

Hebblewhite

Merrill

2022

Ecology

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“…Normandeau et al . (2020) measured infection intensity and prevalence simultaneously, finding that migrants had higher infection in terms of both metrics, which only partially matches theoretical predictions. This empirical finding of higher infection intensity in migrants could represent the rare theoretical case of the reverse pattern (which occurs when transmission of parasites in the migrant environment is high and their survival cost low, compared to parasites in the resident environment; Shaw et al ., 2018).…”

Section: Conceptual Frameworkmentioning

confidence: 87%

How to study parasites and host migration: a roadmap for empiricists

et al. 2022

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Animal migration (round‐trip, predictable movements) takes individuals across space and time, bringing them into contact with new communities of organisms. In particular, migratory movements shape (and are shaped by) the costs and risk of parasite transmission. Unfortunately, our understanding of how migration and parasite infection interact has not proceeded evenly. Although numerous conceptual frameworks (e.g. mathematical models) have been developed, most empirical evidence of migration–parasite interactions are drawn from pre‐existing empirical studies that were conducted using other conceptual frameworks, which limits our understanding. Here, we synthesise and analyse existing work, and then provide a roadmap for future (especially empirical) studies. First, we synthesise the conceptual frameworks that have been developed to understand interactions between migration and parasites (e.g. migratory exposure, escape, allopatry, recovery, culling, separation, stalling and relapse). Second, we highlight current challenges to studying migration and parasites empirically, and to integrating empirical and theoretical perspectives, particularly emphasizing the challenge of feedback loops. Finally, we provide a guide to overcoming these challenges in empirical studies, using comparative, observational and experimental approaches. Beyond guiding future empirical work, this review aims to inspire stronger collaboration between empiricists and theorists studying the intersection of migration and parasite infection. Such collaboration will help overcome current limits to our understanding of how migration and parasites interact, and allow us to predict how these critical ecological processes will change in the future.

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“…Questions here could be framed accordingly, e.g., as 'Here are multiple conflicting empirical data patterns, how do we reconcile them?' For example, some empirical studies find the pattern that migratory individuals typically have greater parasite infection than resident individuals [29,30], while other studies find the opposite pattern [31,32]. Shaw et al [33] used a theoretical model to clarify the mechanism leading to these disparate patterns: migration can simultaneously lead to a higher richness of parasites and lower infection prevalence.…”

Section: Starting With Pattern Focusing On Conflict (The "Mediator")mentioning

confidence: 99%

Six strategies for framing theoretical research questions

Shaw,

Bisesi,

Wojan

et al. 2024

Preprint

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Theory is a small but critical component of the biological research process, and complements observational and experimental approaches. However, early career biologists receive little training on how to frame a theoretical question and, thus, how to evaluate when theory has successfully answered the research question.Here we develop a guide with six verbal framings for theoretical models in biology. These correspond to different roles one might play as a theorist: "Advocate", "Explainer", "Instigator", "Mediator", "Semantician", and "Tinkerer". These are drawn from combinations of two starting points (pattern or mechanism) and three foci (novelty, robustness, or conflict). We illustrate each of these framings with examples of specific theoretical questions, by drawing on recent theoretical papers in the fields of ecology and evolutionary biology. We show how the same research topic can be approached from slightly different perspectives, using different framings. We show how clarifying a model's framing can debunk common misconceptions of theory: that simplifying assumptions are bad, more detail is always better, models show anything you want, and modelling requires substantial math knowledge. Finally, we provide a roadmap that early career researchers can use to identify a framing to serve as a blueprint for their own theoretical research projects.

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Living with liver flukes: Does migration matter?

Cited by 8 publications

References 51 publications

Large herbivores in a partially migratory population search for the ideal free home

Large herbivores in a partially migratory population search for the ideal free home

How to study parasites and host migration: a roadmap for empiricists

Six strategies for framing theoretical research questions

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