Large grazers modify effects of aboveground–belowground interactions on small-scale plant community composition

Aboveground and belowground organisms influence plant community composition by local interactions, and their scale of impact may vary from millimeters belowground to kilometers aboveground. However, it still poorly understood how large grazers that select their forage on large spatial scales interact with small-scale aboveground–belowground interactions on plant community heterogeneity. Here, we investigate how cattle (Bos taurus) modify the effects of interactions between yellow meadow ants (Lasius flavus) and European brown hares (Lepus europaeus) on the formation of small-scale heterogeneity in vegetation composition. In the absence of cattle, hares selectively foraged on ant mounds, while under combined grazing by hares and cattle, vertebrate grazing pressure was similar on and off mounds. Ant mounds that were grazed by only hares had a different plant community composition compared to their surroundings: the cover of the grazing-intolerant grass Elytrigia atherica was reduced on ant mounds, whereas the relative cover of the more grazing-tolerant and palatable grass Festuca rubra was enhanced. Combined grazing by hares and cattle, resulted in homogenization of plant community composition on and off ant mounds, with high overall cover of F. rubra. We conclude that hares can respond to local ant–soil–vegetation interactions, because they are small, selective herbivores that make their foraging decisions on a local scale. This results in small-scale plant patches on mounds of yellow meadow ants. In the presence of cattle, which are less selective aboveground herbivores, local plant community patterns triggered by small-scale aboveground–belowground interactions can disappear. Therefore, cattle modify the consequences of aboveground–belowground interactions for small-scale plant community composition

Estimating adhesive seed-dispersal distances:field experiments and correlated random walks

1. In this study we aimed to estimate distance distributions of adhesively dispersed seeds and the factors that determine them. 2. Seed attachment and detachment were studied using field experiments with a real sheep, a sheep dummy and a cattle dummy. Seed-retention data were used in correlated random walk models to simulate adhesive seed dispersal. 3. Seed attachment to the sheep dummy was larger in quantity and in number of species, and stronger in relation to seed density in the vegetation, than was seed attachment to the cattle dummy. Species found on the real sheep were also found on the sheep dummy. 4. Detachment from sheep wool differed little between smooth, bristly, small or large seeds, but smooth seeds detached from cattle fur within a few metres. Seeds applied within reach of vegetation detached sooner than seeds applied higher on the dummy. 5. The simulations showed that sheep are long-distance seed-dispersal vectors for seeds of any morphology (99 percentile distance, 2.9 km). The virtual cattle and Fallow Deer dispersed bristly and hooked seeds over long distances (99 percentile distance, 435-840 m), but not smooth seeds. Wood Mouse simulations generated only short-distance dispersal (99 percentile distance, 12 m)

Ecological correlates of seed survival after ingestion by Fallow Deer

1. The survival and retention of seeds was studied by feeding known quantities of seeds of 25 species to four captive Fallow Deer (Dama dama L.). To test for ecological correlates, plant species were selected to represent large variation in seed size, seed shape, seed longevity and habitat fertility. 2. Seeds of 24 out of 25 fed plant species survived ingestion and defecation by Fallow Deer. Seed survival ranged between 0.5 and 42% of germinable seeds fed. Time to recover 50% of all seeds defecated by Fallow Deer in faeces averaged 25 h, and ranged from 13 to 38 h. 3. Seed survival was negatively related to seed mass (R = 0.65) and variance of unit seed dimensions (R = -0.56), and positively related to seed longevity (R = 0.40), but not related to habitat fertility. Log(10) of (seed mass x variance of seed dimensions) was the best predictor of seed survival (R = -0.68). 4. The ecological correlates of seed survival presented here can help us to estimate the ability of plant species to disperse seeds over long distances