Behavioral Ecology and Sociobiology最新文献

Abstract

Apex carnivores that rely primarily on predation play a central but complex role within scavenging ecology by potentially suppressing intra-guild competitors, but also facilitating them by providing a reliable supply of carrion. We investigated the competitive relationship between sympatric wolves (Canis lupus) and wolverines (Gulo gulo) in Norway across three seasons. We deployed remote cameras at fresh wolf kills (n = 29) and built Bayesian generalized linear mixed models (GLMMs) to explore the use of fresh wolf-killed prey by sympatric wolves and wolverines. Our results showed that wolves facilitated wolverines by providing scavenging opportunities. Biomass available from wolf kills was influenced by seasonal wolf prey preference and group size. Wolverines visited 100% of wolf kills in fall and winter, whereas only 18% in summer. We found that in winter, wolverines visited wolf kills 3.6 and 6.7 times more often than single wolves and wolf groups revisited their kills, and spent 10 and 25 times as much time at carcasses compared to single wolves and groups of wolves. Thus, wolverines played an important role in the depletion of wolf-killed prey, with potential effects on the scavenging behavior of other guild members. Understanding how globally threatened top predators may function as key species in scavenging processes is important to conservation as this may have community-wide cascading effects and support important ecosystem functions and services.

Significance statement

Large carnivores serve a central role within scavenging ecology through the suppression and facilitation of intraguild competitors. The wolf, as an apex obligate predator, can provide a reliable supply of carrion, that can serve as an important resource to facultative scavengers. However, while facultative behavior helps to mitigate the effects of limited prey for scavengers, it can also increase exposure to competition and intraguild predation. Across three seasons, we explored the use of fresh wolf-killed prey by sympatric wolves and wolverines. Our findings reveal that wolves facilitate wolverines by providing scavenging opportunities, where biomass available from kills is influenced by wolves’ prey preference and group size. Wolverines, like wolves, utilized kills heavily during winter, when increased access to food is important to wolverine reproductive rates. Wolverines exhibited caching behavior, possibly reducing exposure to interspecific competition, while serving an important role in the depletion of carrion biomass.

Co-occurrence of ecologically similar species can lead to direct agonistic interactions, including kleptoparasitism, where one individual consumes trophic resources acquired by another. We documented facultative kleptoparasitism in two similarly-sized raptors, the lesser kestrel (Falco naumanni) and the red-footed falcon (Falco vespertinus). These two species currently co-occur in Northern Italy due to recent range shifts influenced by climate and land-use changes. Multi-year focal observations revealed that single or multiple red-footed falcons were associated with 72% of foraging groups of lesser kestrels. Red-footed falcons initiated kleptoparasitic attacks on lesser kestrels in 46% of foraging group observations, with a success rate of 34%. Attacks were more likely when the prey capture rate (i.e. a proxy of foraging efficiency) of lesser kestrels was high. Red-footed falcons were more successful in stealing prey when the food items carried by lesser kestrels were larger, and kleptoparasitic attacks by groups of red-footed falcons had a higher success rate than attacks by singletons. Overall, we propose that such frequent kleptoparasitic events, which have never been previously documented in these two species, may have emerged as a consequence of their recently established co-occurrence. Kleptoparasitism could reduce the foraging efficiency and fitness of lesser kestrels, potentially leading to broader ecological consequences, such as population declines or range shifts. These findings highlight how species redistributions associated with global changes may lead to novel interspecific interactions with unforeseen ecological implications.

Abstract

Behavioral modifications induced by parasites have been extensively documented across multiple taxa. However, a major challenge is to experimentally determine whether such manipulations confer an adaptive advantage to the parasite. Behavioral alterations in spiders attacked by ichneumonid wasps are characterized by the construction of modified webs. These modified webs can enhance the survival chances of the parasitoid by reducing mortality due to natural enemies and environmental factors during the pupal stage. Additionally, some modified webs offer extra protection by keeping a centrally attached leaf shelter, originally used by the spider as a refuge, where parasitoids can build their cocoon. In these webs, it is possible that web modifications are not critical for the survival of parasitoid pupae. We evaluated the hypothesis that modifications made by parasitized spiders in a web with leaf shelter do not improve the survival of the parasitoid and presented details of behavioral modifications induced by the wasp Zatypota alborhombarta (Ichneumonidae) in its host spider Cryptachaea migrans (Theridiidae). We observed that modified webs built by parasitized spiders had silk thread around the web shelter, reduced vertical lines, and an increase in forked distal ends of lines. However, these changes in the host web did not improve the survival of parasitoid pupae. Our results indicate that the benefits of host behavioral modification for the parasitoids may vary across different host species. In addition, we suggested that the effects of altered web designs may depend on specific host-created web features and environmental factors like predation pressure.

Significance statement

Behavioral manipulations of hosts induced by parasites are often suggested as an adaptive trait, increasing the fitness of the parasitic organism. Still, the influence of host characteristics on the parasite’s fitness is rarely experimentally assessed, raising questions about the extent of the adaptive nature of manipulation. Here, we demonstrate for the first time that behavioral modifications induced by Ichneumonidae wasps in a cobweb spider do not increase the survival of the parasitoids. We argue that the presence of shelters in these webs, used by parasitoids in their pupal stages, provides a safe environment for development, independent of other modifications. Furthermore, we suggest that the behavioral modification reflects the maintenance of a phylogenetically conserved trait.