Sam M. J. G. Steyaert’s research while affiliated with Nord University and other places

Generalist populations often harbor individual dietary specialists. Whether using a narrower set of resources than the population (= specialization) affects specialists' nutrient intake remains underexplored. We evaluated variation in ingredient and nutrient specialization in a European brown bear Ursus arctos population via the Proportional Similarity Index (PSi, from 0 = highly specialized to 1 = not specialized) and assessed associations of specialization with year, season and reproductive class. Different methodologies concerning the organization of raw data for PSi calculations were evaluated (i.e. the resolution of diet compositional data (feces vs the average of all feces per individual) and temporal restrictions for the population (year‐round vs within‐season). Overall, a tendency for ingredient specialization (PSi 0.37 ± 0.14) and absence of nutrient specialization (PSi 0.79 ± 0.10) was observed. Ingredient specialization was mainly influenced by the proportion of berries, graminoids, oats and moose in the diet. Annual, seasonal and reproductive class effects were moderate and did not strongly affect PSi for both ingredients and nutrients. Organizing diet compositional data from a ‘feces resolution' to ‘individual resolution' decreased specialization. Changing the comparative population in PSi calculations from ‘all‐year‐round' to ‘within year and season' also resulted in less pronounced specialization. The degree of specialization was not caused by individuals exhibiting consistent ingredient preferences over the years (low repeatability of PSi) except in spring. Our results suggested absence of nutrient specialization and mild ingredient specialization, which appeared to be an outcome of the ecological circumstances rather than specific individual traits. Additionally, we demonstrated that the methods applied can have substantial influence for the calculation of specialization indices.

Carrion can have disproportionally large effects on ecological processes and community dynamics. During decomposition, the influx of growth‐limiting nutrients can create small‐scale disturbances with high soil cover known as ‘cadaver decomposition islands’ (CDIs). Such disturbances can allow for altered plant species composition, increased biomass production or provide microsites for regeneration. Carcasses also provide a resource for omnivorous scavengers, which have the potential to direct endozoochorous seed dispersal towards developing CDIs. In this study, we investigated functional links between the scavenger community, carcass‐induced disturbances in vegetation and the seedling establishment of berry‐producing ericaceous species. We experimentally placed out 30 vertebrate carcasses of various species in a boreal forest ecosystem, each paired with a control and a mechanically disturbed plot to track vertebrate animal activity (i.e. dispersal vectors), vegetation changes (i.e. recruitment windows) and seedling establishment. We hypothesized that carcass size and season of experimental deposition would affect (H1) scavenger community composition and (H2) formation of CDIs, and that (H3) seedling establishment of ericaceous species is more abundant at CDIs compared with control or disturbed plots without carcass deposition. We found that carcass presence effectively created a spatiotemporal hotspot of animal activity and that 94% of observations of vertebrates at carcasses were of species with the potential for ericaceous seed dispersal. Larger carcasses (e.g. moose, reindeer) attracted similar and abundant vertebrate communities, whereas observations at small carcasses (e.g. red fox) resembled those at control plots (H1). Only larger carcasses led to CDI formation (i.e. potential recruitment microsites), while plots with small carcasses resembled control plots (H2). Surprisingly, the season of carcass deposition did not influence vertebrate composition at carcass plots or CDI formation (H1–2). Seedlings were significantly more abundant in CDIs compared with mechanical disturbance and control plots (H3). Overall, CDIs contained about 4 and 19 times more seedlings compared with disturbed and controls, respectively. Our study demonstrates how individual carcasses in a boreal forest landscape can facilitate sexual reproduction in ericaceous keystone species. We suggest that this pathway also occurs in other ecosystems and that it may contribute to the genetic diversity of plant populations. Read the free Plain Language Summary for this article on the Journal blog.

Ruminants are dependent on their gut microbiomes for nutrient extraction from plant diets. However, knowledge about the composition, diversity, function, and spatial structure of gut microbiomes, especially in wild ruminants, is limited, largely because analysis has been restricted to faeces or the rumen. In two geographically separated reindeer subspecies, 16S rRNA gene amplicon sequencing revealed strong spatial structuring, and pronounced differences in microbial diversity of at least 33 phyla across the stomach, small intestine, and large intestine (including faeces). The main structural feature was the Bacteroidota to Firmicutes ratio, which declined from the stomach to the large intestine, likely reflecting functional adaptation. Metagenome shotgun sequencing also revealed highly significant structuring in the relative occurrence of carbohydrate-active enzymes (CAZymes). CAZymes were enriched in the rumen relative to the small and large intestines. Interestingly, taxonomic diversity was highest in the large intestine, suggesting an important and understudied role for this organ. Despite the two study populations being separated by an ocean and six millennia of evolutionary history, gut microbiome structuring was remarkably consistent. Our study suggests a strong selection for gut microbiome biogeography along the gastrointestinal tract in reindeer subspecies.

Currently, fundamental demographic data for wild Asian black bears (Ursus thibetanus) in Japan are lacking. As a first step toward science-based management, we must improve our understanding of life history characteristics such as reproduction and mortality. This study aimed to quantify the demographic parameters of Asian black bears in central Japan. (1) By measuring the cementum annuli width of the teeth of females, age at first reproduction was estimated to be 5.44 ± 0.22 (mean ± SE) years and reproductive interval 2.38 ± 0.48 years. (2) By counting placental scars in uteri sampled from recovered bear carcasses, we estimated litter size to be 1.58 ± 0.09 cubs and minimum age at primiparity to be two years. (3) We clarified the annual rates of natural mortality (0.108, 95% CI: 0.064–0.174) and human-caused mortality (0.005, 95% CI: 0.002–0.021) by using capture–recapture records for subadult and adult bears. We used observation data from the first six months after birth to estimate cub mortality rate (0.235, 95% CI: 0.080–0.465). Further research will allow us to identify which endogenous and exogenous factors affect demographic parameters and to use these parameters to estimate population dynamics as a next step. Published online 21 July, 2023; Print publication 31 October, 2023

The dietary nutrient profile has metabolic significance and possibly contributes to species' foraging behavior. The brown bear (Ursus arctos) was used as a model species for which dietary ingredient and nutrient concentrations as well as nutrient ratios were determined annually, seasonally and per reproductive class. Brown bears had a vertebrate- and ant-dominated diet in spring and early summer and a berry-dominated diet in fall, which translated into protein-rich and carbohydrate-rich diets, respectively. Fiber concentrations appeared constant over time and averaged at 25% of dry matter intake. Dietary ingredient proportions differed between reproductive classes; however, these differences did not translate into a difference in dietary nutrient concentrations, suggesting that bears manage to maintain similar nutrient profiles with selection of different ingredients. In terms of nutrient ratios, the dietary protein to non-protein ratio, considered optimal at around 0.2 (on metabolizable energy basis), averaged around 0.2 in this study in fall and around 0.8 in spring and summer. We introduced the minimal non-fat to fat ratio necessary for efficient maintenance metabolism. This ratio varied across seasons but never fell beneath the theoretically estimated minimum to ensure metabolic efficiency. This population thus managed to ingest diets that never exerted a lack of glucogenic substrate, suggesting that metabolic efficiency may either be a driver of active diet selection or that natural resources available to bears did not constitute a constraint in this respect. Given the considerable proportion of fiber in the diet of brown bears, the relevance of this nutrient and its role in foraging behavior might be underestimated.

Berry-producing Vaccinium shrubs are keystone species in boreal forest ecosystems and their berries provide an essential food source for many vertebrates. In Fennoscandia, both the abundance and cover of Vaccinium have decreased in forests, with intensive forestry practice as a main driver. Vaccinium seedling recruitment is constricted to recruitment windows of opportunity and appears to be infrequent, mainly due to seed dispersal limitation. Passerine birds are key players in seed dispersal, which can be directed towards perching points such as coarse woody debris. In this study, we investigated the potential for directed endozoochory by passerine birds towards cut stumps and if such stumps were viable recruitment windows for Vaccinium species, in an intensively managed boreal forest landscape of central Norway. We surveyed stump and paired forest floor microsites for passerine scat (i.e. potential seed rain) and Vaccinium seedlings. We collected passerine scat and conducted germination experiments to assess if they contained viable seed. We tested the microsite effect (i.e. forest floor/stump) on scat deposition and seedling establishment and then used modified ensemble classifiers to identify important environmental factors affecting scat deposition and seedling establishment patterns. We found that passerine scat was disproportionally deposited on stumps, and that the vast majority of scat contained viable Vaccinium seed. Stumps were also suitable recruitment windows for Vaccinium species, as a higher probability of seedling establishment occurred at stumps compared with the forest floor. However, scat deposition and seedling establishment at stumps were rather contextual and determined by environmental variables. The probability of scat deposition increased with higher complexity of the vertical forest structure and lower canopy cover, whereas seedling establishment required bryophyte cover and larger stumps, or alternatively smaller stumps with competition-free spaces. Our results highlight a pathway to successful sexual reproduction for Vaccinium species in managed forests: passerine birds direct endozoochorous seed dispersal towards tree stumps, which can offer suitable conditions for seedling establishment. However, the spatiotemporal variability both in forest stand structure and in stump conditions have a strong influence on the success of sexual recruitment via this pathway.

Litter pollution is a global environmental problem that occurs in virtually all ecosystems. Scientific research on anthropogenic litter and its environmental impacts focusses predominantly on plastics and the marine environment. Little empirical knowledge exists about the distribution and ecological impacts of litter in terrestrial environments, where most litter is produced. To start closing that knowledge gap, we investigated the distribution of litter in a cultural landscape in central Norway and in relation to land cover types. We registered and collected litter in 110 survey plots that were randomly stratified across various land cover types. Our results show that land cover type modulates the occurrence, abundance, fragments size, and that litter is most present and abundant in or near land cover types associated with high human activities. Plastic was by far the most common litter material type, although the litter community (in terms of materials type) was not independent from land cover type. This knowledge can help to inform and optimize litter management and clean-up activities in terrestrial landscapes. How and to what extent the spatial structure of the litter community mediates ecological effects across various land cover types remains unknown to a large extent and warrants further study.

In endozoochorous seed dispersal, the ecological characteristics of each disperser determine the quantitative and qualitative aspects of the dispersal mechanism. To understand the role of different frugivores in multispecies seed dispersal networks, it is necessary to focus on the community structure and investigate where in the landscape seed deposition occurs. The aim of this research was to assess the quantitative and qualitative aspects of a mammalian endozoochorous seed dispersal network in a temperate forest ecosystem and identify the seasonal dispersal niche of each member of the assemblage. We hypothesized that differences among dispersers and seasons would occur in (H1) the proportion of scats that contain seeds, seed abundance in scats, and the number of seed species dispersed per scat, and in (H2) the probability of dispersing seeds to suitable microsites for germination of each species and seed abundance. We also hypothesized (H3) that the microhabitat variables of deposition sites would vary among dispersers, and (H4) that complementary structures would occur in terms of dispersers, dispersed species, and deposition sites. From summer (June–August) to autumn (September–November) in 2003 and 2004, we collected scats of five mammalian frugivorous species and recorded eight microhabitat variables at each deposition site in central Japan. We recorded the presence and number of seeds in scats and identified all seed at the species level. We considered a deposition site as suitable when the habitat type (interior forest, treefall gap, forest edge, and outside the forest) at a deposition site matched the microhabitat required for the for the dispersed species to germinate and survive as seedlings. A total of 341 scats containing seeds of 16 fleshy-fruited species were collected. Among these, 213 (62.5%) scats were dispersed to suitable habitats (summer: 68.8%, autumn: 54.8%). We found that the seed abundance in the scat varied among dispersers and was higher in autumn (H1–2). The probability of dispersing seeds to suitable microsites switched among dispersers from summer to autumn (H2). The distinctive microhabitat variables and variation in microhabitat at deposition sites differed among dispersers across seasons (H3). Disperser-plant and disperser-deposition site networks were specialized and modular in structure compared to random networks during both seasons, but there was a less nested structure in summer compared to autumn (H4). The five mammal species showed differences and seasonality in seed dispersal niches. Because of these differences, these mammal species may play redundant and complementary roles in the seed dispersal network.