Implications of sensory ecology for species coexistence: biased perception links predator diversity to prey size distribution

Inherent to sensory systems is a discrepancy between the perceived and the actual environment. We modelled prey perception in different species of echolocating bats and show that differences in sensory systems can be important for shaping the niches of animals and for structuring animal communities. We argue that sensory specialization can lower interspecific competition by making the same world appear different. We specifically raise the claim that it is important to consider the interaction of sensory bias and the distribution of (prey) resource size. Using a modeling approach we assessed the potential contribution of sensory bias for species coexistence for the example of bat echolocation. We show that even relatively small sensory differences among coexisting species can translate into significant differences in access to food resources, if prey size distribution is skewed towards small prey. Specifically, for the prey size distribution occurring most frequently in nature, differences in sensory access to resources seem large enough to relax competition and facilitate species coexistence. Interaction between sensory bias and prey size distribution in a way that enhances species coexistence may be a general phenomenon not limited to bat echolocation.publishe

Mating tactics of male feral goats ( Capra hircus ): risks and benefits

Intense competition between males for reproduction has led to the evolution of alternative mating tactics (AMTs). Feral goat males usually use a tactic called tending, in which they defend oestrous females from other males. Males may also use a second mating tactic called coursing, in which they gain access to oestrous females by disturbing a tending pair. Herein, we examine estimated mating success (EMS) and risks of using these tactics. Tending was only used by mature (≥4 years old), higher-ranking males and accounted for 75% of EMS. Coursing was used by males of all ages and dominance ranks, and accounted for 25% of EMS. Using coursing, male kids achieved 8% of EMS. Mature males achieved 92% of EMS. Both age and dominance rank were related to EMS, but age was not important after its relationship with dominance was controlled. Tending bouts were, on average, ca. 30min long, while coursing bouts only averaged ca. 2min. Males were more likely to suffer a butt while coursing than while tending, and formerly tending males were responsible for most butts. Kids that coursed had the highest risk of being butted. In most AMTs, there are reductions in the risks in relation to low fitness benefits. However, we found that the risks of butts during coursing were high, while our evidence suggests that the EMS was probably low. Nevertheless, the existence of an effective AMT in male feral goats may have an important influence on the intensity of sexual selection and the effective population siz

Matching Morphology and Diet in the Disc-Winged Bat Thyroptera tricolor (Chiroptera)

The dietary niche and morphological adaptations of a species should be highly correlated. However, conflicting selective pressures may make predictions about diet difficult without additional knowledge of a species' life history. We tested the reliability of predicting a bat's diet from its wing morphology using data for Spix's disk-winged bat (Thyroptera tricolor). The species had been predicted to fall within either the aerial hawking or gleaning foraging group. We compared the results of a theoretical (canonical discriminant function analysis of morphology) and an applied (analysis of droppings) method of diet determination. Our results place T. tricolor in the gleaning functional group with a 77% probability according to morphology. Correspondingly, a large proportion of the diverse diet consisted of nonflying prey, such as spiders, insect larvae, and other silent prey, which should be difficult to detect using echolocation. Although some flying prey were taken, it is clear that T. tricolor regularly gleans prey from surfaces, indicating that for this species, morphology is a useful indicator of diet. However, the breadth of the diet; the high proportion of jumping spiders, leafhoppers, and insect larvae; and the extremely small size of prey were unique features of the diet that could not be predicted from morphology alone. Thus, although comparative statistical methods and the analysis of wing morphology may be helpful to predict the general ecological niche, only detailed investigation of the life history may yield the detail needed for understanding the link between morphology and ecology of individual specie

Experience does not change the importance of wind support for migratory route selection by a soaring bird

Publisher Copyright: © 2022 The Authors.Migration is a complex behaviour that is costly in terms of time, energy and risk of mortality. Thermal soaring birds rely on airflow, specifically wind support and uplift, to offset their energetic costs of flight. Their migratory routes are a record of movement decisions to negotiate the atmospheric environment and achieve efficiency. We expected that, regardless of age, birds use wind support to select their routes. Because thermal soaring is a complex flight behaviour that young birds need to learn, we expected that, as individuals gain more experience, their movement decisions will also increasingly favour the best thermal uplift conditions. We quantified how route choice during autumn migration of young European honey buzzards (Pernis apivorus) was adjusted to wind support and uplift over up to 4 years of migration and compared this with the choices of adult birds. We found that wind support was important in all migrations. However, we did not find an increase in the use of thermal uplifts. This could be due to the species-specific learning period and/or an artefact of the spatio-temporal scale of our uplift proxies.Peer reviewe

Simulation experiment to test strategies of geomagnetic navigation during long-distance bird migration

The project was funded by the Leverhulme Trust (Research Project Grant RPG-2018-258).Background Different theories suggest birds may use compass or map navigational systems associated with Earth’s magnetic intensity or inclination, especially during migratory flights. These theories have only been tested by considering properties of the Earth’s magnetic field at coarse temporal scales, typically ignoring the temporal dynamics of geomagnetic values that may affect migratory navigational capacity. Methods We designed a simulation experiment to study if and how birds use the geomagnetic field during migration by using both high resolution GPS tracking data and geomagnetic data at relatively fine spatial and temporal resolutions in comparison to previous studies. Our simulations use correlated random walks (CRW) and correlated random bridge (CRB) models to model different navigational strategies based on underlying dynamic geomagnetic data. We translated navigational strategies associated with geomagnetic cues into probability surfaces that are included in the random walk models. Simulated trajectories from these models were compared to the actual GPS trajectories of migratory birds using 3 different similarity measurements to evaluate which of the strategies was most likely to have occurred. Results and conclusion We designed a simulation experiment which can be applied to different wildlife species under varying conditions worldwide. In the case of our example species, we found that a compass-type strategy based on taxis, defined as movement towards an extreme value, produced the closest and most similar trajectories when compared to original GPS tracking data in CRW models. Our results indicate less evidence for map navigation (constant heading and bi-gradient taxis navigation). Additionally, our results indicate a multifactorial navigational mechanism necessitating more than one cue for successful navigation to the target. This is apparent from our simulations because the modelled endpoints of the trajectories of the CRW models do not reach close proximity to the target location of the GPS trajectory when simulated with geomagnetic navigational strategies alone. Additionally, the magnitude of the effect of the geomagnetic cues during navigation in our models was low in our CRB models. More research on the scale effects of the geomagnetic field on navigation, along with temporally varying geomagnetic data could be useful for further improving future models.Publisher PDFPeer reviewe

Simulating geomagnetic bird navigation using novel high-resolution geomagnetic data

The project was funded by the Leverhulme Trust [Research Project Grant RPG-2018-258].Birds rely on precise navigational mechanisms, especially for long-distance migrations. One debated mechanism is their use of the geomagnetic field. It is unclear if and how different species of birds are using intensity or inclination (or both) for navigation. Previous geomagnetic modelling research is based on static geomagnetic data despite a temporally and spatially varying geomagnetic field. Animals supposedly have a high sensitivity to those changes of the geomagnetic field. In order to understand how birds respond in real-time to its temporal variation, we need to use accurate geomagnetic information linked to the position of the bird through co-location in space and time. We developed a data-driven approach to simulate geomagnetic migratory strategies, using, for the first time, accurate contemporaneous geomagnetic data obtained from Swarm satellites of the European Space Agency. We created biased correlated random walk models which were based on both GPS data from greater white-fronted geese (Anser albifrons) during fall migration between north-west Russia and central Europe and contemporaneous satellite geomagnetic data. Different strategies of geomagnetic navigation associated with different geomagnetic values were translated into probability surfaces, built from geomagnetic data, and included into the random walk models. To evaluate which strategy was most likely, we compared the measured GPS trajectories to the simulated trajectories using different trajectory similarity measurements. We propose this as an approach to track many bird species for future comparative studies. We found that navigational strategies in these geese using magnetic intensity were closer to the observed data than those using inclination. This was the case in 80% of the best models and is an indication that it should be more beneficial for these geese to use intensity over inclination. Additionally, our results supported results from a previous study, that navigation based on taxis and compass mechanisms were more similar to the observed data than other mechanisms. We therefore suggest that these geese may use a combination of these strategies for navigation at a broad-scale. Overall, it seems likely that for successful navigation to the target location more than one mechanism is necessary; indicating a multifactorial navigation mechanism of these migratory geese in the study area. The satellite geomagnetic data are available at a higher temporal resolution and the use significantly improved the fit of the modelled simulations in comparison to the modelled geomagnetic data. Therefore, using annotated geomagnetic data could greatly improve the modelling of animal geomagnetic navigation in future research.Publisher PDFPeer reviewe

Flexibility of habitat use innovel environments:Insights from a translocation experiment with Lesser Black-backed Gulls

Being faced with unknown environments is a concomitant challenge of species' range expansions. Strategies to cope with this challenge include the adaptation to local conditions and a flexibility in resource exploitation. The gulls of the Larus argentatus-fuscus-cachinnans group form a system in which ecological flexibility might have enabled them to expand their range considerably, and to colonize urban environments. However, on a population level both flexibility and local adaptation lead to signatures of differential habitat use in different environments, and these processes are not easily distinguished. Using the lesser black-backed gull (Larus fuscus) as a system, we put both flexibility and local adaptation to a test. We compare habitat use between two spatially separated populations, and use a translocation experiment during which individuals were released into novel environment. The experiment revealed that on a population-level flexibility best explains the differences in habitat use between the two populations. We think that our results suggest that the range expansion and huge success of this species complex could be a result of its broad ecological niche and flexibility in the exploitation of resources. However, this also advises caution when using species distribution models to extrapolate habitat use across space

Habitat use during spring migration: Remote sensing meets movement ecology

Forage availability during spring migration is crucial for the survival and successful reproduction of many migratory species. With careful timing in relation to spring growth and small-scale selection of suitable food sites, large avian herbivory migrants are known to maximise foraging rate during spring. However, especially for Arctic breeders, the recent levels of climate and habitat change alter the conditions that they meet at their spring stopover and breeding sites. In the EO-MOVE project we examine the habitat use of greater white-fronted geese (Anser albifrons) along their spring migration route between central Europe and northern Russia. This species is known to be sensitive to land-use intensity, phenology and landscape configuration, which calls for the exploitation of high resolution tracking and remote sensing technologies. To characterise the movement of geese within their spring stopovers, we use over 150 highly resolved GPS tracks of individual adult geese from the years 2006-2017. Since 2014 we have additionally collected acceleration data to classify the animals' behaviour and energy expenditure. We select within-stopover GPS positions that are classified as flight or feeding and overlay the movements connecting different small-scale feeding sites with optical and SAR time series data (20Ã-20m) from the Sentinel 1 and 2 satellite missions using step selection functions. Habitat preference outcomes are then set into context with vegetation indices and compared between individuals, years and stopover sites. First results indicate that white-fronted geese generally select for highly green, low and young vegetation, but also that there are large differences between stopovers. We expect to reveal in detail how the birds select for suitable feeding sites in relation to availability and recent levels of habitat change, potentially allowing for site selection prediction, an important prerequisite for spatially or temporally targeted conservation schemes

Integrating animal movement with habitat suitability for estimating dynamic landscape connectivity

Context: High-resolution animal movement data are becoming increasingly available, yet having a multitude of trajectories alone does not allow us to easily predict animal movement. To answer ecological and evolutionary questions at a population level, quantitative estimates of a species' potential to act as a link between patches, populations, or ecosystems are of importance. Objectives: We introduce an approach that combines movement-informed simulated trajectories with an environment-informed estimate of their ecological likelihood. With this approach, we estimated connectivity at the landscape level throughout the annual cycle of bar-headed geese (Anser indicus) in its native range. Methods: We used a tracking dataset of bar-headed geese to parameterise a multi-state movement model and to estimate temporally explicit habitat suitability within the species' range. We simulated migratory movements between range fragments, and estimated their ecological likelihood. The results are compared to expectations derived from published literature. Results: Simulated migrations matched empirical trajectories in key characteristics such as stopover duration. The estimated likelihood of simulated migrations was similar to that of empirical trajectories. We found that the predicted connectivity was higher within the breeding than in wintering areas, corresponding to previous findings for this species. Conclusions: We show how empirical tracking data and environmental information can be fused to make meaningful predictions about future animal movements. These are temporally explicit and transferable even outside the spatial range of the available data. Our integrative framework will prove useful for modelling ecological processes facilitated by animal movement, such as seed dispersal or disease ecology

A Comprehensive Model for the Quantitative Estimation of Seed Dispersal by Migratory Mallards

Long-distance seed dispersal is an important ecosystem service provided by migratory animals. Plants inhabiting discrete habitats, like lakes and wetlands, experience dispersal limitation, and rely heavily on zoochory for their spatial population dynamics. Granivorous waterbirds may disperse viable seeds of wetland plants over long distances during migration. The limited knowledge of waterbird migration has long hampered the evaluation of the importance of waterbirds in seed dispersal, requiring key metrics such as realistic dispersal distances. Using recent GPS tracking of mallards during spring migration, we built a mechanistic seed dispersal model to estimate realistic dispersal distances. Mallards are abundant, partially migratory ducks known to consume seeds of >300 European plant species. Based on the tracking data, we informed a mallard migration simulator to obtain a probabilistic spring migration model for the mallard population wintering at Lake Constance in Southern Germany. We combined the spring migration model with seed retention curves to develop seed dispersal kernels. We also assessed the effects of pre-migratory fasting and the availability of suitable deposition habitats for aquatic and wetland plants. Our results show that mallards at Lake Constance can disperse seeds in the northeastern direction over median distances of 293 and 413 km for seeds with short and long retention times, respectively, assuming a departure immediately after foraging. Pre-migratory fasting strongly affected the dispersal potential, with only 1–7% of ingested seeds left for dispersal after fasting for 12 h. Availability of a suitable deposition habitat was generally <5% along the migratory flyway. The high probability of seed deposition in a freshwater habitat during the first stopover, after the mallards completed the first migratory flight, makes successful dispersal most likely to happen at 204–322 km from Lake Constance. We concluded that the directed long-distance dispersal of plant seeds, realized by mallards on spring migration, may contribute significantly to large scale spatial plant population dynamics, including range expansion in response to shifting temperature and rainfall patterns under global warming. Our dispersal model is the first to incorporate detailed behavior of migratory waterbirds and can be readily adjusted to include other vector species when tracking data are available