The functional response is at the core of any predator-prey interactions as it establishes the link between trophic levels. The use of inaccurate functional response can profoundly affect the outcomes of population and community models. Yet most functional responses are evaluated using phenomenological models which often fail to discriminate among functional response shapes and cannot identify the proximate mechanisms regulating predator acquisition rates. Using a combination of behavioral, demographic, and experimental data collected over 20 years, we develop a mechanistic model based on species traits and behavior to assess the functional response of a generalist mammalian predator, the arctic fox (Vulpes lagopus), to various tundra prey species (lemmings and the nests of geese, passerines, and sandpipers). Predator acquisition rates derived from the mechanistic model were consistent with field observations. Although acquisition rates slightly decrease at high goose nest and lemming densities, none of our simulations resulted in a saturating response in all prey species. Our results highlight the importance of predator searching components in predator-prey interactions, especially predator speed, while predator acquisition rates were not limited by handling processes. By combining theory with field observations, our study provides support that the predator acquisition rate is not systematically limited at the highest prey densities observed in a natural system. Our study also illustrates how mechanistic models based on empirical estimates of the main components of predation can generate functional response shapes specific to the range of prey densities observed in the wild. Such models are needed to fully untangle proximate drivers of predator-prey population dynamics and to improve our understanding of predator-mediated interactions in natural communities.
Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator–prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey – lemmings (preferred prey) and snow geese (alternate prey) – which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long‐term dataset (21 years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator–prey interactions and our capacity to anticipate food web response to ongoing climate change.
Seabirds are the most endangered group of birds and among them, the gadfly petrels (genera Pseudobulweria and Pterodroma) are the most threatened and least known. The Mascarene Petrel (Pseudobulweria aterrima) is endemic to Réunion Island and is one of the rarest birds in the world. This species was considered extinct in the mid-20th century but was rediscovered in 1970. The population is thought to be in decline because of predation by invasive predators, habitat destruction, and light-induced mortality. The first goal of this paper is to detail the methods that we used to discover the breeding colonies of this species and to determine the threats at these sites. The second goal is to present characteristics of the colonies we found, the threats occurring at these colonies, and the first conservation actions implemented at these sites. We first conducted an island-scale acoustic survey using autonomous recording units (ARUs) to locate the breeding colonies. We then used infrared thermal binoculars to precisely locate the places where birds displayed and landed. Because all discovered breeding sites were on vertical cliffs, we abseiled these cliffs to access the nests. Once burrows were discovered, we deployed infrared camera traps to determine the presence of alien predators or competitors (rats, cats, tenrecs) and to study the behaviors of the birds at the colony. The large-scale acoustic survey revealed the presence of 17 vocally active sites, 16 of which were investigated with infrared thermal binoculars. We observed petrel landings at five of these sites. Two of them were accessible and we abseiled to find the nests. We found 14 occupied burrows at one of these sites and eight at the other. Camera traps revealed the presence of rats and tenrecs at both sites, and cats were detected close to the colonies. The two colonies are on tall vertical cliffs covered with native vegetation, at elevations of 650 m a. s. l. and 1250 m a. s. l., respectively. These findings allowed us to implement conservation actions, such as invasive mammal control, and to start long-term monitoring and applied research for conservation. We are confident that the methods we developed could be used with great success at other places where finding colonies of a cryptic, rare, and nocturnal seabird is particularly challenging.RESUMEN. Las aves marinas son el grupo de aves más amenazado y entre ellas los géneros Pseudobulweria y Pterodroma son los más amenazados y poco conocidos. Pseudobulweria aterrima es endémica de la isla de Reunión y es una de las aves más raras del mundo. Esta especie fue considerada extinta a mediados del siglo 20 pero fue redescubierto en 1970. Se supone que la población está en disminución debido a la depredación por especies invasoras, destrucción del hábitat y la mortalidad inducida por la luz. El primer objetivo de este estudio es detallar los métodos que utilizamos para descubrir las colonias de reproducción de esta especie y determinar las amenazas en estos sitios. El segundo objetivo es presentar las caracter...
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