Arethusa bulbosa is a northeastern North American orchid species rare in most of its range. This study sought to determine the factors associated with the presence of Arethusa within peatlands and its absence from a priori suitable sites. Twenty-four plots with Arethusa were compared with paired plots from which the species was absent and with 22 plots in peatland where the species has never been present. Vegetation and abiotic variables were recorded within the plots, and anthropogenic variables were identified using aerial photographs. The IndVal method was used to determine whether some species were characteristic of Arethusa habitat, and discriminant function analyses were performed to determine which factors were related to occupied and unoccupied sites. No characteristic species were identified when comparing paired plots. Occupied sites were mainly characterized by lower light availability at ground level (46%; mean), higher Floristic Quality Assessment Index (35), and smaller shrubs (55 cm) than unoccupied paired plots (61%, 32, and 61 cm respectively) from the same peatland. Water pH was the main factor discriminating occupied sites (5.5) from the unoccupied sites in peatlands where the species has never been present (3.9), pH being usually higher in plots with Arethusa. Ten species were characteristic of plots with Arethusa (including Larix laricina, Sphagnum palustre, and Aulacomnium warnstorfii) when compared to a priori suitable sites. Overall, our results suggest that Arethusa settles in poor to moderate Sphagnumdominated fen habitats rather than typical open bog habitats, as usually assumed.

It is generally assumed that blue and great tits (Cyanistes caeruleus, Parus major) compete for the same type of food (Lepidoptera larvae) during the breeding season and that the former have some advantage because they are usually earlier and can exploit small caterpillars that are often more abundant and are not consumed by great tits. However, it is not clear whether, when confronted with similar circumstances (e.g., nestling demand), blue and great tits show similar preferences for a particular caterpillar type. In this 2-y study, we compare the diet of both tit species in detail by controlling for hatching date and brood size. We also examine how the contribution of caterpillars and spiders to the diet is related to nestling development. A positive relationship was found between the percentage of spiders in the diet and nestling tarsus length in both species, reinforcing the idea that neonatal nutrition could have a strong influence on nestling phenotype (e.g., offspring size). Such a correlation may arise because spiders contain a high level of taurine, an essential nutrient in the early development of young, and/or this prey type contains more calcium than other food items, which may affect the rate of nestling bone mineralization. Blue tits fed their young double the number of tortricid larvae in comparison with great tits, whereas the latter showed a clear preference for noctuids and exploited, with a low frequency, a type of larvae not consumed by blue tits, hairy caterpillars (Lasiocampidae). Our results point to resource partitioning by these species in this forest ecosystem and contribute to a better understanding of feeding ecology of titmice, which is particularly timely in a global warming context.

Ants are important consumers in most terrestrial ecosystems. They show a great diversity of diets and foraging strategies. Here, we analyzed how circannual variation in resource use by the Mediterranean species Aphaenogaster senilis is related to colony life cycle and resource availability. In southwestern Spain, this species is active almost year-round, but foraging intensity decreases 10-fold between March and November, following larval production. In the summer, ants refrain from foraging at midday to avoid high temperatures. We hypothesized that diet and foraging plasticity could also explain the ecological success of this species. There are several techniques for assessing the diet of ants. Combining isotope analyses with conventional methods can provide better taxonomic resolution of resource utilization. Using a combination of classic and isotopic analyses, we found that 1) the proportion of plant and animal-derived items collected by foragers did not vary significantly from March to November, and 2) isotope analyses indicated a decrease in the trophic level of A. senilis between June and September, suggesting a difference between collected material and items assimilated. Interestingly, most animal prey were collected by individual ants, and many were retrieved alive. Therefore, A. senilis is not only a scavenger, but also a non-negligible predator, particularly of aphids. The abundance of the most common animal-derived items in the diet was proportional to their abundance in the study area. We conclude that A. senilis is an opportunistic species that is able to feed on a variety of resources, which may be key to its ecological success.

Fluctuations in the distribution and abundance of prey resources are an important influence on the foraging ecology of carnivores. Spatio-temporal variation in the diet of river otters (Lontra canadensis), however, is not well understood. In addition, we have limited knowledge about seasonal changes in otter activity at latrine sites and how these changes may relate to changes in otter diet. We used a combination of scat content and stable-isotope analyses to assess the contributions of different prey items to otter diet. We investigated the spatio-temporal variation in the availability of prey groups as it influenced the composition of otter diet and the number of scat deposited at latrine sites. A combination of fish spawning period, water-body type, and lake best described the presence of salmonidae, minnows, and insects in otter scats. The number of scats was best described by a two-week calendar time measurement and geographic location. Scat deposition was positively influenced by a time period when no fish were spawning (early July) and the kokanee (Oncorhynchus nerka) spawning period (early September). In general, the stable-isotope analysis agreed with the results of the scat content analysis: fish dominated the diet, with lesser contributions from other prey items. The stable-isotope analysis, however, suggested that sockeye salmon, larger species of fish (burbot, lake trout), and birds contributed more than was revealed by scat content analysis. Management strategies require accurate and unbiased information on wildlife distribution and abundance that is often measured from surveys of sign; this study provides some of the critical information needed to interpret surveys for river otters. We also suggest implications for other wildlife species.

Differential traits (e.g., feeding at different heights in trees) have evolved to allow the coexistence of putative competitors; such traits have been well studied in small passerines (e.g., Paridae), mainly during the winter. However, few studies have been carried out during the breeding season, when competition could be more intense. We applied here a multidimensional approach, examining ecological (prey type and size, and nesting habitat characteristics) and life history (timing of maximum nestling food demand) traits that might help to explain the coexistence of great (Parus major), crested (Lophophanes cristatus), and coal (Periparus ater) tits breeding in a Mediterranean pine forest. The diets of great and crested tit nestlings were equally diverse, and more diverse than that of coal tit nestlings. Prey size diversity was similar among species. Great and crested tits consumed longer caterpillars than coal tits. This last species preferred to build its nests in nest boxes surrounded by mature vegetation, while great tits preferred immature vegetation and crested tits preferred intermediate vegetation stages. Finally, the breeding cycles of both great and coal tits overlapped to a great extent, while crested tits bred earlier. In summary, each species has a unique combination of niche characteristics that might contribute to the coexistence of the 3 tit species.

During the breeding season, seabird colonies are attended by active breeders, failed breeders, and non-breeding birds. Determining breeding status of some seabirds can be challenging, but tracking non-breeder attendance can provide important information on the health of the colony or the local marine environment. We used behavioural and energetic data to distinguish between breeding and non-breeding northern fulmars (Fulmarus glacialis) at a colony in the Canadian High Arctic, a region where global warming is rapidly changing the marine environment in which these birds feed. Breeding fulmars could be distinguished from non-breeders based on their larger fat reserves, although body mass and morphometrics taken in the field were not sufficient to distinguish breeding classes reliably. Behavioural cues also signaled fulmar breeding status, but observing these cues required a considerable amount of observation time. As environmental conditions in the Arctic continue to change, monitoring and population modeling efforts will require detailed observation periods rather than rapid assessments to reliably assess proportions of non-breeding fulmars at Arctic colonies.

The effects of sika deer (Cervus nippon) browsing and understory productivity on web-building spiders' density were experimentally examined. We particularly focused on the nonlinear effects of these 2 factors and their underlying mechanisms. Our field experiments controlling deer density and understory productivity revealed that the deer affected the densities of 2 abundant spider species nonlinearly: the deer effect was unimodal or constant in lower productivity plots and negative in higher productivity plots. The nonlinear effects seemed to occur because the response trend of the spiders' limiting factors to deer impact differed between lower and higher productivity plots. In lower productivity plots, the density of the most abundant spider species, Prolinyphia longipedella, was limited by dicot cover, and both spider density and dicot cover had unimodal-shaped responses to deer density. This spider species was limited by the availability of twigs in higher productivity plots and responded negatively to deer density. Deer seemed to affect web-building spider density in understory vegetation by changing the number of available sites for webs through browsing. However, the precise limiting factors differed with understory productivity. Since forest understory productivity is expected to show large variation at various spatial scales due to differences in canopy tree density, the availability of nutrients, and other environmental factors, considering nonlinear effects is important when predicting the impact of large herbivores on invertebrates in forest understories.

Interactions between ants and vertebrate-dispersed fleshy fruits are common on the floor of tropical forests. These interactions are considered beneficial to seeds if ants clean the seed (which may prevent fungal contamination and/or increase germination success) or act as secondary fine-scale dispersers (depositing the seed in nearby nutrient-enriched nest sites). Benefits to seeds, however, may be constrained by limited ant access to fruits. Here, we experimentally tested whether ant access to fallen fleshy fruits of Psychotria suterella (Rubiaceae) can be affected by previous handling (including ingestion) by birds. We found that mandibulated fruits and fruits embedded in feces are more prone to be visited by ants compared to entirely intact fruits. Moreover, the number of ant species per station was higher for vertebrate-handled fruit categories. We suggest that ongoing vertebrate loss in tropical forests may affect this highly opportunistic and potentially mutualistic interaction.

The spread and efficacy of biological control agents are thought to increase with the regional frequency of host populations. We tested this hypothesis by quantifying the occurrence of and damage by 2 biocontrol agents, Galerucella pusilla and G. calmariensis beetles, on 52 introduced stands of purple loosestrife (Lythrum salicaria) in Ontario, Canada. An analysis of herbarium records combined with population-genetic analysis of style morph frequencies and extensive field observations made across Ontario over a 25-y period indicate that L. salicaria populations are more densely distributed in eastern than central Ontario. However, we did not detect the control agents more frequently nor was damage by biocontrol agents higher in 14 eastern stands than 17 central stands. By comparing 20 stands where beetles had been deliberately released with 32 for which there is no recorded history of beetle release, we found that beetles had spread widely beyond documented release sites. However, plants at release sites were more heavily damaged than those at non-release sites, such that previous surveys monitoring only release sites overestimated the efficacy of control. Overall, we detected herbivory by Galerucella spp. in 88% of L. salicaria stands throughout eastern and central Ontario, and only 5% of 5957 plants sampled seem to have entirely escaped damage. We recommend an iterative post-release monitoring study to determine the broader efficacy of the control program using the baseline quantitative data presented here.