Environmental predictability as a cause and consequence of animal movement

The impacts of environmental predictability on the ecology and evolution of animal movement have been the subject of vigorous speculation for several decades. Recently, the swell of new biologging technologies has further stimulated their investigation. This advancing research frontier, however, still lacks conceptual unification and has so far focused little on converse effects. Populations of moving animals have ubiquitous effects on processes such as nutrient cycling and seed dispersal and may therefore shape patterns of environmental predictability. Here, we synthesise the main strands of the literature on the feedbacks between environmental predictability and animal movement and discuss how they may react to anthropogenic disruption, leading to unexpected threats for wildlife and the environment

Communal and efficient movement routines can develop spontaneously through public information use

Animal aggregations occur in almost all taxa and can be strongly influential for consumer-resource dynamics and population health. Their adaptive value and underlying mechanisms are thus fundamental questions. Many animals use information about resource locations inadvertently broadcasted by other individuals through visual, acoustic, or olfactory cues. Such simple, involuntary information transfer is commonly employed in groups of social animals. However, it remains unknown whether public information use could have been the initial cause of social aggregations. Here, using agent-based modeling, in the absence of inclusive fitness benefits or direct conspecific attraction, we show that the use of ephemeral public information about resource locations can cause memory-based foragers to spontaneously and permanently aggregate into communal home ranges that take the form of movement circuits (also called traplines) along which individuals travel asynchronously. Even though experienced individuals only rely on their personal memory to inform their movement decisions, we find that the use of public information during the learning phase is very beneficial in the long term because the communal circuits are more efficient than those established by individuals that do not use public information. Our results reveal how simple, inadvertent information transfer between naïve, selfish foragers can cause the emergence of long-term aggregations, which are a prerequisite for the evolution of more complex social behaviors. They also suggest that individuals may not necessarily need to witness the entire sequences of actions performed by others to converge to the same behavioral routines

Spatial memory shapes density dependence in population dynamics

Most population dynamics studies assume that individuals use space uniformly, and thus mix well spatially. In numerous species, however, individuals do not move randomly, but use spatial memory to visit renewable resource patches repeatedly. To understand the extent to which memorybased foraging movement may affect density-dependent population dynamics through its impact on competition, we developed a spatially explicit, individual-based movement model where reproduction and death are functions of foraging efficiency. We compared the dynamics of populations of with- and without-memory individuals. We showed that memory-based movement leads to a higher population size at equilibrium, to a higher depletion of the environment, to a marked discrepancy between the global (i.e. measured at the population level) and local (i.e. measured at the individual level) intensities of competition, and to a nonlinear density dependence. These results call for a deeper investigation of the impact of individual movement strategies and cognitive abilities on population dynamics

Mobility and its sensitivity to fitness differences determine consumer–resource distributions

An animal's movement rate (mobility) and its ability to perceive fitness gradients (fitness sensitivity) determine how well it can exploit resources. Previous models have examined mobility and fitness sensitivity separately and found that mobility, modelled as random movement, prevents animals from staying in high-quality patches, leading to a departure from an ideal free distribution (IFD). However, empirical work shows that animals with higher mobility can more effectively collect environmental information and better sense patch quality, especially when the environment is frequently changed by human activities. Here, we model, for the first time, this positive correlation between mobility and fitness sensitivity and measure its consequences for the populations of a consumer and its resource. In the absence of consumer demography, mobility alone had no effect on system equilibria, but a positive correlation between mobility and fitness sensitivity could produce an IFD. In the presence of consumer demography, lower levels of mobility prevented the system from approaching an IFD due to the mixing of consumers between patches. However, when positively correlated with fitness sensitivity, high mobility led to an IFD. Our study demonstrates that the expected covariation of animal movement attributes can drive broadly theorized consumer–resource patterns across space and time and could underlie the role of consumers in driving spatial heterogeneity in resource abundance

Foraging efficiency in temporally predictable environments: is a long-term temporal memory really advantageous?

Cognitive abilities enabling animals that feed on ephemeral but yearly renewable resources to infer when resources are available may have been favoured by natural selection, but the magnitude of the benefits brought by these abilities remains poorly known. Using computer simulations, we compared the efficiencies of three main types of foragers with different abilities to process temporal information, in spatially and/or temporally homogeneous or heterogeneous environments. One was endowed with a sampling memory, which stores recent experience about the availability of the different food types. The other two were endowed with a chronological or associative memory, which stores long-term temporal information about absolute times of these availabilities or delays between them, respectively. To determine the range of possible efficiencies, we also simulated a forager without temporal cognition but which simply targeted the closest and possibly empty food sources, and a perfectly prescient forager, able to know at any time which food source was effectively providing food. The sampling, associative and chronological foragers were far more efficient than the forager without temporal cognition in temporally predictable environments, and interestingly, their efficiencies increased with the level of temporal heterogeneity. The use of a long-term temporal memory results in a foraging efficiency up to 1.16 times better (chronological memory) or 1.14 times worse (associative memory) than the use of a simple sampling memory. Our results thus show that, for everyday foraging, a long-term temporal memory did not provide a clear benefit over a simple short-term memory that keeps track of the current resource availability. Long-term temporal memories may therefore have emerged in contexts where short-term temporal cognition is useless, i.e. when the anticipation of future environmental changes is strongly needed

Drivers of site fidelity in ungulates

1. 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. 2. 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. 3. Mule deer Odocoileus hemionus and moose Alces alces exhibited relatively strong site fidelity, while wildebeest Connochaetes taurinus and barren‐ground caribou Rangifer tarandus granti had 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. 4. 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. 5. 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

Remembering and coming back : a theoretical and methodological approach to recursive movement strategies and their population-level consequences

Les patrons récursifs de déplacement, où l’individu revient à des sites déjà visités, sont très répandus. L’utilisation de la mémoire, supposée être avantageuse lorsque l’environnement est prévisible, pourrait être sous-jacente à l’émergence de ces patrons. Cependant, notre compréhension de l’interface mémoire-déplacement a jusqu'à présent été limitée par un manque de méthodes adaptées et d’investigation théorique des avantages de l’utilisation de la mémoire et des patrons qui en émergent. Au cours de cette thèse j’ai cherché à combler en partie ces manques. Je propose ici trois nouveaux cadres d'analyse des patrons récursifs de déplacement. Le premier délimite les zones les plus fréquemment revisitées par un individu, le deuxième détecte la périodicité dans les revisites de sites connus, et le troisième définit formellement et quantifie la routine de déplacement en termes de répétitivité de la séquence de déplacement, et propose un algorithme pour détecter les sous-séquences répétées. A l'aide d'un modèle individu-centré, nous montrons que l'utilisation de la mémoire dans un environnement prévisible est très avantageuse énergétiquement comparée à une stratégie de recherche sans mémoire, y compris en situation de compétition, et qu'elle mène à l'émergence de domaines vitaux stables et à la ségrégation spatiale entre individus. L'utilisation de la mémoire invalide plusieurs hypothèses très courantes faites par les études populationnelles, en menant à une forte déplétion de l’environnement, à une augmentation de la taille de la population à l’équilibre, et à une relation non linéaire entre la taille de population totale et l’intensité de compétition localement ressentie par les individus. Ainsi, ma thèse contribue à une meilleure compréhension des conséquences de la mémoire sur la valeur sélective des individus, sur les patrons de déplacement, et sur la démographie des populations. Elle propose des méthodes innovantes pour quantifier et caractériser les patrons récursifs de déplacement pouvant émerger de son utilisation. Ces méthodes devraient ouvrir de nouvelles opportunités de comparaisons entre individus de différentes populations ou espèces qui permettront le test d'hypothèses sur les pressions de sélection favorisant l'utilisation de la mémoire.Recursive movement patterns, by which an individual returns to already visited sites, are very common. Memory use, hypothesized to be advantageous when the environment is predictable, could underlie the emergence of these patterns. However, our understanding of the memory-movement interface has been limited by two knowledge gaps. We still lack appropriate methodologies and theoretical knowledge of the advantages of memory use and of the patterns that emerge from it. During this PhD project, I aimed at filling in some of these gaps. I present here three new frameworks for the analysis of recursive movement patterns. The first one delimits the areas most frequently revisited by an individual, the second one detects periodic revisit patterns, and the third one formally defines and quantifies routine movement behaviour in terms of movement sequence repetitiveness, and presents an algorithm that detects the sub-sequences that are repeated. Using an individual-based model, we show that memory use, when the environment is predictable, is very energetically advantageous compared to foraging strategies that do not use memory, including in a situation of competition, and that it leads to the emergence of stable Home Ranges and spatial segregation between individuals. Memory use invalidates several hypotheses very commonly made in population studies, by leading to a stronger environmental depletion, to a higher equilibrium population size, and to a nonlinear relationship between the total population size and the individually-experienced intensity of competition. Therefore, my PhD thesis contributes to a better understanding of the consequences of memory use for the fitness of individuals, for movement patterns, and for population dynamics. It offers innovative methodologies that quantify and characterize recursive movement patterns that can emerge from its use. These methods should open new opportunities for the comparison of the movements of individuals from different populations and species, and thus the testing of hypotheses about the pressures that select for memory use

Dispersers’ habitat detection and settling abilities modulate the effect of habitat amount on metapopulation resilience

International audienceContext: Metapopulation theory makes useful predictions for conservation in fragmented landscapes. For randomly distributed habitat patches, it predicts that the ability of a metapopulation to recover from low occupancy level (the “metapopulation capacity”) linearly increases with habitat amount. This prediction derives from describing the dispersal between two patches as a function of their features and the distance separating them only, without interaction with the rest of the landscape. However, if individuals can stop dispersal when hitting a patch (“habitat detection and settling” ability), the rest of habitat may modulate the dispersal between two patches by intercepting dispersers (which constitutes a “shadow” effect).Objectives: We aim at evaluating how habitat detection and settling ability, and the subsequent shadow effect, can modulate the relationship between the metapopulation capacity and the habitat amount in the metapopulation.Methods: Considering two simple metapopulation models with contrasted animal movement types, we used analytical predictions and simulations to study the relationship between habitat amount and metapopulation capacity under various levels of dispersers’ habitat detection and settling ability.Results: Increasing habitat detection and settling ability led to: (i) larger metapopulation capacity values than expected from classic metapopulation theory and (ii) concave habitat amount–metapopulation capacity relationship.Conclusions: Overlooking dispersers’ habitat detection and settling ability may lead to underestimating the metapopulation capacity and misevaluating the conservation benefit of increasing habitat amount. Therefore, a further integration of our mechanistic understanding of animals’ displacement into metapopulation theory is urgently needed

Data from: From randomness to traplining: a framework for the study of routine movement behavior

Memory allows many animals to benefit from the spatial predictability of their environment by revisiting known profitable places. Travel route optimization or resource acquisition constraints usually lead to repeated sequences of visits, which may have major evolutionary and ecological implications. However, the study of this behavior has been impaired by a lack of concepts and methodologies. We here formally define routine movement behavior, provide an index that quantifies the degree of repetitiveness in movement sequences in terms of minimal conditional entropy, and design a flexible procedure that detects the specific subsequences that are repeated. We demonstrate our framework using computer simulations and real-world movement data of black-tailed deer (Odocoileus hemionus) introduced into a novel environment. The simulation example showed that our methods can suitably reveal the increase in the level of routine movement behavior during home range (HR) establishment. Black-tailed deer did not show such an increase, suggesting that HR establishment occurred very fast. In both examples, our procedure determining the subsequences that are repeated provides a precise visualization of routine movements. Our approach solves limitations in the study of routine movement behavior and thus opens promising perspectives for the study of the linkages between cognition, foraging strategies, and environments. Although we developed it to study routine movement behavior, it can be applied to any type of behavioral sequence and should thus be of interest to a broad range of behavioral ecologists

The disturbance of resident populations of field voles (Microtus agrestis) by immigrants

The introduction of immigrants into resident populations may disturb the social organisation of the latter. It is often stated that males compete with males for access to mates, while females compete with females and/or males for limited resources (e.g., nest sites, food). Therefore, the impacts of introductions on residents should depend on the immigrant’s sex. To test this hypothesis, we experimentally introduced either male or female immigrants into field vole (Microtus agrestis) populations, and observed the consequences in terms of space use and survival of both residents and immigrants. Our results showed intra-sexual competition: (i) resident females responded to the introduction of females by reducing their home range size and their interactions with neighbours; (ii) immigrant males suffered high mortality, probably due to contests with resident males for access to females. We conclude that the role of social interactions should not be underestimated when releasing unfamiliar individuals into small populations