Ecologically based definition of seasons clarifies predator–prey interactions

Species interactions within food webs are driven by multiple constraints, including those imposed by seasonal changes in the environment. Ecologically sound definitions of seasons may therefore be a prerequisite for clarifying predator prey interactions. Most studies define biological seasons based on fixed schedules or on temporal changes in a single movement measurement. We used a novel clustering approach based on homogeneous space‐use patterns of GPS‐collared animals to reveal 7 biological seasons for caribou Rangifer tarandus caribou, and 5 for both moose Alces alces and grey wolves Canis lupus interacting in a boreal ecosystem. Subsequent evaluation of niche overlap showed that, as predicted, wolves had a stronger spatio‐temporal connection with moose, its main prey, than with caribou. Movement constraints and limiting resource distributions similarly affected all species in some instances, but also caused temporal changes in the extent of niche overlap between wolves and its two prey. The risk that caribou faced was not only linked to the niche overlap with wolves, but also to the extent of wolf‐moose niche overlap during the same period. Food‐web properties emerged from the analysis, with temporal changes in relative niche overlap reflecting the strength of trophic interactions during the year. Our study demonstrates how the study of trophic interactions can benefit from comprehensive definitions of biological seasons.     

Divergent host phenotypes create opportunities and constraints on the distribution of two wing‐dwelling feather mites

The diversity of symbionts (commensals, mutualists or parasites) that share the same host species may depend on opportunities and constraints on host exploitation associated with host phenotype or environment. Various host traits may differently influence host accessibility and within‐host population growth of each symbiont species, or they may determine the outcome of within‐host interactions among coexisting species. In turn, phenotypic diversity of a host species may promote divergent exploitation strategies among its symbiotic organisms. We studied the distribution of two feather mite species, Proctophyllodes sylviae and Trouessartia bifurcata, among blackcaps Sylvia atricapilla wintering in southern Spain during six winters. The host population included migratory and sedentary individuals, which were unequally distributed between two habitat types (forests and shrublands). Visual mite counts showed that both mite species often coexisted on sedentary blackcaps, but were seldom found together on migratory blackcaps. Regardless of host habitat, Proctophyllodes were highly abundant and Trouessartia were scarce on migratory blackcaps, but the abundance of both mite species converged in intermediate levels on sedentary blackcaps. Coexistence may come at a cost for Proctophyllodes, whose load decreased when Trouessartia was present on the host (the opposite was not true). Proctophyllodes load was positively correlated with host wing length (wings were longer in migratory blackcaps), while Trouessartia load was positively correlated to uropygial gland size (sedentary blackcaps had bigger glands), which might render migratory and sedentary blackcaps better hosts for Proctophyllodes and Trouessartia, respectively. Our results draw a complex scenario for mite co‐existence in the same host species, where different mite species apparently take advantage of, or are constrained by, divergent host phenotypic traits. This expands our understanding of bird–mite interactions, which are usually viewed as less dynamic in relation to variation in host phenotype, and emphasizes the role of host phenotypic divergence in the diversification of symbiotic organisms.     

Using functional traits to investigate the determinants of crustacean zooplankton community structure

Understanding the various processes contributing to community assembly is among the central aims of ecology. As a means of exploring this topic we quantified the relative influences of habitat filtering and competition in establishing patterns of community functional trait diversity across a landscape of lakes. Habitat filtering has been invoked in shaping community structure when co‐occurring taxa are more similar in their traits than expected by chance (under‐dispersion), and competition has been inferred as a structuring agent when co‐occurring taxa are less similar (over‐dispersion). We tested these hypotheses in crustacean zooplankton communities using a functional trait‐based approach based on five traits defining zooplankton feeding and habitat preferences across 51 lakes spanning several large limnological gradients. In general, zooplankton communities were functionally less diverse than random assemblages created from the same regional species pool. Furthermore, functional diversity was strongly correlated with variables related to lake productivity, suggesting that access to resources was the chief habitat filtering process constraining zooplankton functional diversity. This pattern was driven by the predominantly herbivorous cladocerans as opposed to the more commonly omnivorous, and sometimes carnivorous, copepods.     

Seasonal fluctuations of resource abundance and avian feeding guilds across forest–farmland boundaries in tropical Africa

Seasonal fluctuations in climatic factors are expected to increase in future decades. However, little is known about the response of tropical species communities to seasonal fluctuations in climate and resource availability, particularly across different habitat types. We examined the relationship between spatio‐temporal fluctuations in the abundance of fruits and invertebrates and two avian feeding guilds, i.e. frugivores and insectivores, in forest and farmland habitats in western Kenya. Fruits and invertebrates fluctuated substantially throughout the year, but seasonal fluctuations were asynchronous between the two habitat types. Species richness and total abundance of frugivores and insectivores also fluctuated strongly and were closely related to the abundance of their respective resources. Frugivore species richness fluctuated anti‐cyclical in forest and farmland habitats, suggesting that several frugivorous species tracked fruit resources across habitat boundaries. In contrast, insectivorous bird richness fluctuated synchronously in the two habitat types, suggesting a lack of local‐scale movements across habitat boundaries. We conclude that bird communities strongly respond to seasonal fluctuations in resource availability, but responses differ between feeding guilds. While frugivores seem to respond flexibly to seasonal fluctuations, for instance by tracking fruit resources across habitat boundaries, insectivorous birds appear to be more susceptible to the expected increase in seasonal fluctuations in resource availability.     

Can we disentangle predator–prey interactions from species distributions at a macro‐scale? A case study with a raptor species

There is a debate on whether an influence of biotic interactions on species distributions can be reflected at macro‐scale levels. Whereas the influence of biotic interactions on spatial arrangements is beginning to be studied at local scales, similar studies at macro‐scale levels are scarce. There is no example disentangling, from other similarities with related species, the influence of predator–prey interactions on species distributions at macro‐scale levels. In this study we aimed to disentangle predator–prey interactions from species distribution data following an experimental approach including a factorial design. As a case of study we selected the short‐toed eagle because of its known specialization on certain prey reptiles. We used presence–absence data at a 100 km2 spatial resolution to extract the explanatory capacity of different environmental predictors (five abiotic and two biotic predictors) on the short‐toed eagle species distribution in peninsular Spain. Abiotic predictors were relevant climatic and topographic variables, and relevant biotic predictors were prey richness and forest density. In addition to the short‐toed eagle, we also obtained the predictor's explanatory capacities for 1) species of the same family Accipitridae (as a reference), 2) for other birds of different families (as controls) and 3) artificial species with randomly selected presences (as null models). We run 650 models to test for similarities of the short‐toed eagle, controls and null models with reference species, assessed by regressions of explanatory capacities. We found higher similarities between the short‐toed eagle and other species of the family Accipitridae than for the other two groups. Once corrected by the family effect, our analyses revealed a signal of predator–prey interaction embedded in species distribution data. This result was corroborated with additional analyses testing for differences in the concordance between the distributions of different bird categories and the distributions of either prey or non‐prey species of the short‐toed eagle. Our analyses were useful to disentangle a signal of predator–prey interactions from species distribution data at a macro‐scale. This study highlights the importance of disentangling specific features from the variation shared with a given taxonomic level.     

Another call for the end of invasion biology

The restriction of invasion biology to non‐native species has been laid down as one founding principle of the discipline by many researchers. However, this split between native and non‐native species is highly controversial. Using a phenomenological approach and a more pragmatic examination of biological invasions, the present paper discusses how this dichotomy has restricted the relevance of the field, both from theoretical and practical viewpoints. We advocate the emergence of a broader disciplinary field.     

Parasites as prey in aquatic food webs: implications for predator infection and parasite transmission

While the recent inclusion of parasites into food‐web studies has highlighted the role of parasites as consumers, there is accumulating evidence that parasites can also serve as prey for predators. Here we investigated empirical patterns of predation on parasites and their relationships with parasite transmission in eight topological food webs representing marine and freshwater ecosystems. Within each food web, we examined links in the typical predator–prey sub web as well as the predator–parasite sub web, i.e. the quadrant of the food web indicating which predators eat parasites. Most predator– parasite links represented ‘concomitant predation’ (consumption and death of a parasite along with the prey/host; 58–72%), followed by ‘trophic transmission’ (predator feeds on infected prey and becomes infected; 8–32%) and predation on free‐living parasite life‐cycle stages (4–30%). Parasite life‐cycle stages had, on average, between 4.2 and 14.2 predators. Among the food webs, as predator richness increased, the number of links exploited by trophically transmitted parasites increased at about the same rate as did the number of links where these stages serve as prey. On the whole, our analyses suggest that predation on parasites has important consequences for both predators and parasites, and food web structure. Because our analysis is solely based on topological webs, determining the strength of these interactions is a promising avenue for future research.     

New highlights about the enigmatic marine snake Palaeophis maghrebianus (Palaeophiidae; Palaeophiinae) from the Ypresian (Lower Eocene) phosphates of Morocco

Abstract: Palaeophis maghrebianus belongs to the Palaeophiinae (Palaeophiidae). This snake subfamily is relatively poorly known, and it is mainly represented by disarticulated vertebrae and ribs and by a few vertebral segments. Its intracolumnar variability remains also poorly understood. The discovery of new isolated vertebrae and vertebral segments of Palaeophis maghrebianus in the Ypresian (Lower Eocene) Phosphates of Morocco enables us to provide a more detailed diagnosis of this species and to describe its intracolumnar variability. Moreover, the new material reveals that this species could reach gigantic size being, with Palaeophis colossaeus, one of the two longer palaeophiids. The microanatomical and histological analysis of some vertebrae illustrating diverse positions along the vertebral column reveals the presence of osteosclerosis, especially in the anterior and mid‐precloacal regions. The occurrence of this osseous specialization implies a role in buoyancy and body trim control in this taxon, which is considered a shallow marine dweller based on its anatomical features and geological data. Palaeophis maghrebianus also displays a dense vascular network suggesting a growth speed, and thus a metabolic rate, much higher than in the biggest extant snakes.     

Willow seedlings from photooxidized seeds accelerate cotyledon death and anticipate first leaf emergence: a histological and biochemical study following germination

In willow seeds, photooxidative damage is mainly restricted to the outer cotyledonary tissues, significantly reducing normal germination. Here we analyzed the damage generated in cotyledonary tissues and investigated whether the increase in reactive oxygen species (ROS) generation in seedlings from photooxidized seeds can affect the morphogenetic capacity of the shoot apical meristem. Seeds were photooxidized under different light intensities and the evolution of the damage during seedling growth was studied by light and transmission electron microscopies. The level of lipid peroxidation and changes in antioxidant capacity were measured following the time course of superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase enzyme activities, and the effect of photooxidative stress on the genesis of new leaf primordia and lateral roots was examined. Early and active endocytosis and autophagy, changes in chloroplast morphology, as well as the accumulation and diffusion of ROS all play important roles in the early cell death observed in cotyledonary tissues. Following germination, seedlings from photooxidized seeds anticipated the emergence of first leaves, which complemented the altered functionality of the damaged cotyledons.