Automated VHF-Radio Telemetry Reveals Resource-Driven Site Utilisation Patterns in a Small-Bodied, Highly Mobile Bird (Erythrura Gouldiae)

BackgroundInformation on site utilisation and movement is essential for managing species' resource requirements. Collecting these data requires frequent location sampling of multiple individuals, which can be challenging for small-bodied animals due to the often-large size of animal-borne satellite-based telemetry devices. We show how coded VHF-radio nano-transmitters and an array of passive receivers to collect location data at sufficient frequency and accuracy can be utilised to test whether the highly mobile and small-bodied Gouldian finch adheres to optimal foraging theory within a landscape of high spatiotemporal heterogeneity.MethodsCoded VHF-radio nano-transmitters (0.23 g wt.) were attached to 38 Gouldian finches (Erythrura gouldiae; < 12g bd. wt). Tagged birds were then detected by an array of 6 passive VHF-radio receivers (~ 530 m detection range) spread over 120 km2. We tracked the tagged birds during two sessions corresponding with high and low abundance of their primary food resource (Sorghum spp. seed). The mean and total duration that an individual spent within any receiver detection field (residence time) were used as dependants in a generalised linear mixed model approach within a Bayesian framework to assess the influence of tracking session, life stage, receiver site, and release site. Network analysis revealed the importance of specific areas for the finches within the receiver array using the proportional time a bird spent within any receiver's detection field and the movement between adjacent detection fields. ResultsThe daily mean and total duration that a tagged individual spent within a receiver detection field decreased by ~50% between periods of high and low seed availability, while the extent of movements across the landscape increased with a decline in seed resources. These data support the hypothesis that the Gouldian finch adheres to optimal foraging theory to survive periods of food scarcity. ConclusionsThe data collected via passive telemetry technology support the hypothesis that the Gouldian finch adheres to optimal foraging theory and uses alternative behavioural strategies to survive periods of food scarcity. Specifically, we found that Gouldian finches reduced the time spent foraging within a patch, increased the frequency of transit flights among patches, and expanded the size of their activity space as grass resources declined.

Réflexions sur la proportion du lapin de garenne (Oryctolagus cuniculus) dans le régime alimentaire des chasseurs-cueilleurs autour du Dernier Maximum Glaciaire en Ibérie

Hoy en día el conejo europeo (Oryctolagus cuniculus) es considerado invasivo en varios países. Sin embargo, los motivos del inicio de la explotación de este lagomorfo en el Paleolítico Superior en la península ibérica son objeto de un intenso debate sin que todavía exista un consenso general sobre las causas que explican su introducción en la dieta de los cazadores-recolectores ibéricos. En este artículo, primero presentamos cómo su caza comenzó antes del Último Máximo Glacial (UMG), aumentando durante este periodo. Luego evaluamos las principales hipótesis del Modelo de Amplitud de Dieta (Diet Breadth Model), desarrollado a partir de la Teoría del Forrajeo Óptimo (Optimal Foraging Theory). Este modelo (a veces implícito) es el origen de algunas de estas hipótesis, pero hasta ahora nunca se había aplicado de forma concreta al UMG en la península ibérica. En consecuencia, nosotros lo hemos hecho y los resultados obtenidos no parecen apoyar las hipótesis que defienden una intensificación de la explotación del medio ambiente. Sugerimos que el aprovechamiento de este taxon en torno al UMG en Iberia podría explicarse más bien por el uso de redes entre varias personas. [fr] Bien qu’aujourd’hui le lapin de garenne (Oryctolagus cuniculus) soit considéré comme une espèce invasive dans plusieurs pays, il fait l’objet d’un débat intense quant aux raisons du début de son exploitation durant le Paléolithique supérieur dans la péninsule ibérique. Cependant, aucun consensus général n’existe afin d’expliquer les causes de son introduction dans la diète des chasseurs-cueilleurs ibériens. Ici, nous présentons d’abord que sa chasse a débuté avant le Dernier Maximum Glaciaire (DMG) et qu’elle s’est accrue durant cette période. Ensuite, nous évaluons les principales hypothèses soutenues à partir du Modèle Classique du Régime Alimentaire (MCRA; Diet Breadth Model) issu de la Théorie de l’Approvisionnement Optimal (TAO; Optimal Foraging Theory). Bien que ce modèle soit à l’origine (parfois implicitement) de plusieurs de ces hypothèses, il n’a jamais été appliqué concrètement au DMG dans la péninsule. Nous avons alors appliqué ce modèle et les résultats obtenus ne semblent pas appuyer les hypothèses soutenant une intensification de l’exploitation de l’environnement. Plutôt, nous suggérons que l’utilisation de filets par plusieurs personnes pourrait expliquer l’exploitation de ce taxon autour du DMG en Ibérie.

Less is worse than none: ineffective adaptive foraging can destabilise food webs

Consumers can potentially adjust their diet in response to changing resource abundances, thereby achieving better foraging payoffs. Although previous work has explored how such adaptive foraging scales up to determine the structure and dynamics of food webs, consumers may not be able to perform perfect diet adjustment due to sensory or cognitive limitations. Whether the effectiveness of consumers' diet adjustment alters food-web consequences remains unclear. Here, we study how adaptive foraging, specifically the effectiveness (i.e. rate) with which consumers adjust their diet, influences the structure, dynamics, and overall species persistence in synthetic food webs. We model metabolically-constrained optimal foraging as the mechanistic basis of adaptive diet adjustment and ensuing population dynamics within food webs. We compare food-web dynamical outcomes among simulations sharing initial states but differing in the effectiveness of diet adjustment. We show that adaptive diet adjustment generally makes food-web structure resilient to species loss. Effective diet adjustment that maintains optimal foraging in the face of changing resource abundances facilitates species persistence in the community, particularly reducing the extinction of top consumers. However, a greater proportion of intermediate consumers goes extinct as optimal foraging becomes less-effective and, unexpectedly, slow diet adjustment leads to higher extinction rates than no diet adjustment at all. Therefore, food-web responses cannot be predicted from species' responses in isolation, as even less-effective adaptive foraging benefits individual species (better than non-adaptive) but can harm species' persistence in the food web as a whole (worse than non-adaptive). Whether adaptive foraging helps or harms species coexistence has been contradictory in literature. Our finding that it can stabilise or destabilise the food web depending on how effectively it is performed help reconcile this conflict. Inspired by our simulations, we deduce that there may exist a positive association between consumers' body size and adaptive-foraging effectiveness in the real world. We also infer that such effectiveness may be higher when consumers cognise complete information about their resources, or when trophic interactions are driven more by general traits than by specific trait-matching. We thereby suggest testable hypotheses on species persistence and food-web structure for future research, in both theoretical and empirical systems.

Foraging behavior and patch size distribution jointly determine population dynamics in fragmented landscapes

Increased fragmentation caused by habitat loss presents a major threat to the persistence of animal populations. Whereas the negative effects of habitat loss on biodiversity are well-known, the effects of fragmentation per se on population dynamics and ecosystem stability remain less understood. How fragmentation affects populations is strongly determined by the rate at which individuals can move between separated habitat patches within the fragmented landscape. Here, we use a computational, spatially explicit predator-prey model to investigate how the interplay between fragmentation per se and optimal foraging behavior influences predator-prey interactions and, ultimately, ecosystem stability. We study cases where prey occupies isolated habitat patches and let predators disperse between patches following a Lévy random walk. Our results show that both the Lévy exponent and the degree of fragmentation strongly determine coexistence probabilities. Brownian and ballistic predators go extinct in highly fragmented landscapes and only scale-free predators can coexist with prey. Furthermore, our results reveal that predation causes irreversible loss of prey habitat in highly fragmented landscapes due to the overexploitation of smaller patches. Moreover, our results show that predator movement can reduce, but not prevent not minimize, the amount of irreversibly lost habitat. Our results suggest that incorporating optimal foraging theory into population- and landscape ecology models is crucial to assess the impact of fragmentation on biodiversity and ecosystem stability.

Model for finding the number of honey bee colonies needed for the optimal foraging process in a specific geographical location

Finding a proper location for a bee apiary is a crucial task for beekeepers and especially for travelling beekeepers. Normally beekeepers choose an appropriate apiary location based on their previous experience and sometimes the location may not be optimal for the bee colonies. This can be explained by different flowering periods, variation of resources at the known fields, as well as other factors. In addition it is very challenging to evaluate how many bee colonies should be placed in one geographical location for an optimal nectar foraging process. This research presents a model for finding the number of honey bee colonies needed for the optimal foraging process in the specific location, taking into account several assumptions. Authors propose to take into account potential field productivity, possible chemical contamination, surroundings of the apiary. To run the model, several steps have to be completed, starting from the selection of area of interest, conversion to polygons for further calculations, defining the roads in the selected area. The outcome of the model number of colonies that should be placed is presented to the user. The Python language was used for the model development. The model can be extended to use additional factors and values to increase the precision of the evaluation. In addition, input from users (farmers, agricultural specialists, etc.) about external factors that can affect the number of bee colonies in the apiary can be taken into account. This work is conducted within the Horizon 2020 FET project HIVEOPOLIS (Nr.824069).

Optimal Foraging

This chapter is a refresher on the prey model of classic optimal foraging theory through the lens of this book. I build on the multi-species functional response, the selection ideas, and the parameter breakdown presented in the preceding chapters to argue for how optimal foraging might arise. I rederive the models and suggest that optimal foraging theory may still be relevant to understanding predator–prey interactions, in particular in the context of multi-species functional responses. I also address the possibility that predators mostly have broad diets because they experience low prey abundances most of the time in nature.

Horizontal-vertical movement relationships: Adélie penguins forage continuously throughout provisioning trips

Background Diving marine predators forage in a three-dimensional environment, adjusting their horizontal and vertical movement behaviour in response to environmental conditions and the spatial distribution of prey. Expectations regarding horizontal-vertical movements are derived from optimal foraging theories, however, inconsistent empirical findings across a range of taxa suggests these behavioural assumptions are not universally applicable. Methods Here, we examined how changes in horizontal movement trajectories corresponded with diving behaviour and marine environmental conditions for a ubiquitous Southern Ocean predator, the Adélie penguin. Integrating extensive telemetry-based movement and environmental datasets for chick-rearing Adélie penguins at Béchervaise Island, we tested the relationships between horizontal move persistence (continuous scale indicating low [‘resident’] to high [‘directed’] movement autocorrelation), vertical dive effort and environmental variables. Results Penguins dived continuously over the course of their foraging trips and lower horizontal move persistence corresponded with less intense foraging activity, likely indicative of resting behaviour. This challenges the traditional interpretation of horizontal-vertical movement relationships based on optimal foraging models, which assumes increased residency within an area translates to increased foraging activity. Movement was also influenced by different environmental conditions during the two stages of chick-rearing: guard and crèche. These differences highlight the strong seasonality of foraging habitat for chick-rearing Adélie penguins at Béchervaise Island. Conclusions Our findings advance our understanding of the foraging behaviour for this marine predator and demonstrates the importance of integrating spatial location and behavioural data before inferring habitat use.

Changes in surface water drive the movements of Shoebills

Animal movement is mainly determined by spatial and temporal changes in resource availability. For wetland specialists, the seasonal availability of surface water may be a major determinant of their movement patterns. This study is the first to examine the movements of Shoebills (Balaeniceps rex), an iconic and vulnerable bird species. Using GPS transmitters deployed on six immature and one adult Shoebills over a 5-year period, during which four immatures matured into adults, we analyse their home ranges and distances moved in the Bangweulu Wetlands, Zambia. We relate their movements at the start of the rainy season (October to December) to changes in Normalized Difference Water Index (NDWI), a proxy for surface water. We show that Shoebills stay in the Bangweulu Wetlands all year round, moving less than 3 km per day on 81% of days. However, average annual home ranges were large, with high individual variability, but were similar between age classes. Immature and adult Shoebills responded differently to changes in surface water; sites that adults abandoned became drier, while sites abandoned by immatures became wetter. However, there were no differences in NDWI of areas used by Shoebills before abandonment and newly selected sites, suggesting that Shoebills select areas with similar surface water. We hypothesise that the different responses to changes in surface water by immature and adult Shoebills are related to age-specific optimal foraging conditions and fishing techniques. Our study highlights the need to understand the movements of Shoebills throughout their life cycle to design successful conservation actions for this emblematic, yet poorly known, species.