Questions In African savannas, Macrotermes termites contribute to small‐scale heterogeneity by constructing large mounds. Operating as islands of high nutrient and water availability and low fire frequency, these mounds support distinct, diverse communities of trees that have been shown to be highly attractive to browsers. However, the distinct traits of tree species on termite mounds have hardly been studied, even though this may help to understand processes determining (1) their characteristic community structure and (2) attractiveness for browsers. Here, we compare functional trait and browser preference values between tree species on and off termite mounds. Location Hluhluwe‐iMfolozi Park, Kwazulu‐Natal, South Africa. Methods We recorded tree community compositions for 16 large Macrotermes natalensis mounds and 16 control plots of 100 m2 each in a paired design. For each observed tree species we measured 22 traits, related to water and nutrient use, fire tolerance, light competition and anti‐herbivore defence, and compared average trait values between mound and control communities. Furthermore, we investigated the feeding preferences of ungulate browsers for the most common tree species and how this was linked to their associated traits. Results Termite mounds supported tree communities that were distinct from the surrounding savanna vegetation. Mounds hosted more evergreen and less leguminous tree species than control communities, and the dominant species were less mechanically defended, less nutritious, had larger leaves and lower wood density than the species dominating control plots. Browsers preferred leguminous tree species with high leaf N and P content, which were relatively rare on termite mounds. Conclusions Overall, we conclude that termite mounds in this savanna form small refuges for tree species that seem less adapted to fire (more evergreens), have low nutrient availability (less nitrogen fixers) and suffer from water stress (larger leaf sizes) than typical savanna trees. Surprisingly, despite their reputation as browsing hotspots, the tree species dominating mounds are less nutritious and less preferred by browsers than tree species of the surrounding savanna, which may be explained by the relatively nutrient‐rich nature of this savanna or intraspecific trait differences.

The relative importance of niche‐based (e.g., competitive or stress‐based) and stochastic (e.g., random dispersal) processes in structuring ecological communities is frequently analyzed by studying trait distributions of co‐occurring species. While filtering processes, such as the exclusion of stress‐intolerant species from particular habitats, increase the trait similarity between co‐occurring species, other processes, such as resource competition, can limit the similarity of co‐occurring species. Comparing the observed trait distribution patterns in communities to null expectations from randomized communities (e.g., a draw of the same observed richness from the regional pool) therefore gives a first indication of the dominant process driving community assembly. However, such comparisons do not inform us about the relative contribution of these different processes in shaping community compositions in case of their joint operation (a likely scenario). Using an Approximate Bayesian Computation approach, we develop a new method that allows inference of the relative importance of dispersal, filtering, and limiting similarity processes for the assembly of observed communities with known species and trait composition. We applied this approach to a tree community data set, collected across 20 plots along strong rainfall and fire gradients in a South African savanna. Based on comparisons with simulations, we find that our new approach is powerful in identifying which community assembly scenario has the highest probability to generate the observed trait distribution patterns, while traditional null model comparisons perform poorly in detecting signs of limiting similarity. For the studied savanna tree communities, our analysis yields that dispersal processes are most important in shaping the functional trait distribution patterns. Furthermore, our models indicate that filtering processes were relatively most important in areas with high fire frequencies, while limiting similarity processes were relatively most important in areas with low fire frequency and high rainfall. We conclude that our new method is a promising improvement on current approaches to estimate the relative importance of community assembly processes across different species groups, ecosystems, and biomes. Future model modifications (e.g., the inclusion of individual‐based processes) could provide further steps in uncovering the underlying assembly processes behind observed community patterns.

Premise of research. African grass communities are dominated by two distinct functional types: tall, caespitose bunch grasses and short, spreading lawn grasses. Functional type coexistence has been explained by differences in defoliation tolerance, because lawn grasses occur in intensively grazed areas while bunch grasses are less associated with heavy grazing. If different responses to tissue loss explain their distribution, expectations are that biomass production and leaf-level physiology will be negatively impacted in bunch relative to lawn grasses.Methodology. We tested the influence of defoliation on three lawn and three bunch grasses from Tanzania and South Africa by quantifying growth and measuring physiological response of these grasses to simulated herbivory in a glasshouse experiment. Specifically, we measured photosynthesis, transpiration, stomatal conductance, leaf dry matter content (LDMC), specific leaf area (SLA), leaf nitrogen, and leaf pigment concentrations in leaves of bunch and lawn grasses that were clipped or unclipped.Pivotal results. In contrast to our expectations, clipped lawn and bunch grasses did not differ in photosynthesis, leaf nitrogen, or biomass production, and both lawn and bunch grasses upregulated photosynthesis in response to clipping. However, defoliated bunch grasses had higher rates of stomatal conductance and transpiration compared with defoliated lawn grasses. Also, leaf carotenoid concentrations increased in response to clipping for both functional types but much more in bunch than in lawn grasses. An analysis of leaf-level physiological relationships with structural equation modeling showed that lawn and bunch grasses exert control over carbon gain in different ways. In bunch grasses, net carbon gain was associated with leaf-level structural properties (LDMC and SLA) that varied in response to defoliation, while in lawn grasses, increased carbon gain was the result of increased leaf [N] subsequent to defoliation.Conclusions. The varied responses of lawn and bunch grasses to defoliation appear to arise from their different investments in defense and carbon assimilation subsequent to defoliation. Bunch grasses invest relatively more in carotenoid production, likely as a mechanism to enhance regrowth and protect costly leaves from photodamage. Moreover, bunch grasses maintain efficient carbon assimilation by structural adjustments in leaves (decreasing LDMC subsequent to defoliation), while lawn grasses maintain efficient water use by increasing leaf [N] subsequent to defoliation. Thus, we conclude that a key difference between lawn and bunch grasses is not defoliation tolerance per se but physiological adaptations that constrain them to environments with different moisture availability subsequent to defoliation.

Abstract1. Broad-scale land conversions and fertilizer use have dramatically altered the available staging area for herbivorous long-distance migrants. Instead of natural land, these birds rely increasingly on pastures for migratory fuelling and stopover, often conflicting with farming practices. To predict and manage birds' future habitat use, the relative advantages and disadvantages of natural (e.g. saltmarsh, intertidal) versus anthropogenic staging sites for foraging need to be understood.2. We compared the migratory staging of brent geese on saltmarsh and pasture sites in spring. Food quality (nitrogen and fibre content), antagonistic behaviour, and body weight were quantified at nearby sites in simultaneous seasons. Individuals were tracked with high-resolution GPS and accelerometers to compare timing of migration and time budgets during fuelling.3. On pastures, birds rested more and experienced higher ingestion rates, similar or superior food quality and reduced antagonistic interactions than on saltmarsh.4. Brent geese using fertilized grasslands advanced their fuelling and migration schedules compared to those using saltmarsh. Pasture birds reached heavy weights earlier, departed sooner, and arrived in the Arctic earlier.5. Intertidal mudflats were frequently visited by saltmarsh birds during the day, and available food there (algae, some seagrass) was of higher quality than terrestrial resources. Availability of intertidal resources was an important factor balancing the otherwise more favourable conditions on pastures relative to saltmarsh.6. Synthesis and applications. Disadvantages of longer foraging effort, more antagonistic interactions and delayed fuelling schedules on traditional saltmarshes may cause geese to exchange this traditional niche in favour of pastures, especially in a warming climate that requires advancement of migratory schedules. However, due to its high quality, intertidal forage can complement terrestrial foraging, potentially removing the incentive for habitat switches to pastures. The relatively high quality of green algae and seagrass, and birds' remarkable preference for these resources when available, provides a key for managers to create landscapes that can sustain this special- | INTRODUC TI ONHuman activity is altering our planet's surface in rapid and pervasive ways. Over 80% of the earth's land mass is now under direct human influence (Sanderson et al., 2002), with croplands and pastures occupying over 40% of the total area (Asner, Elmore, Olander, Martin, & Harris, 2004;Foley, 2005). Migratory birds need to navigate these humanaltered landscapes during their seasonal migration and depend on them as alternatives to lost natural habitat. Especially, agricultural land plays an important role in supporting migratory bird communities year-round:pastures provide wintering and breeding grounds to meadow passerines, waterfowl and waders (Knopf, 1994); rice fields (Elphick, 2015;Lourenço, Mandema, Hooijmeijer, Granadeiro, & Piersma, 2010) (Abraham, Jefferies, & Alisauskas, ...

1. Nutrient availability in terrestrial ecosystems has been found to vary along regional climatic and soil gradients and drive variation in plant community composition and vegetation structure. However, more local biotic feedbacks also affect nutrient availability, but their importance in determining vegetation structure relative to regional drivers is yet unclear. 2. Mesic African savannas form a transition zone between the dry grasslands with relatively low nitrogen availability (indicated by low plant N:P ratios) and the wet woodlands of the continent characterized by relatively low phosphorous availability (high plant N:P ratios). They host strong feedback mechanisms of both vegetation and consumers, where large grazers can create short grazing lawns that alternate over short distances with tall fire-dominated bunch grasslands, and patches dominated by woody species with abundant macrodetritivores. Here, we test if such local biotic interactions can overrule regional, landscape-level drivers of plant nutrient availability. 3. In a South African savanna, we find that plant N:P ratios, N and P resorption efficiencies and proficiencies, were indeed much stronger affected by small-scale biotic-created heterogeneity than by a regional rainfall gradient (530-830 mm yr À1 ). Furthermore, we observe that differences in N:P ratios between vegetation structural types are not caused by simple differences in inherent plant traits. 4. This suggests that availability of N and P to plants is strongly contingent on the local biotic interplay between different vegetation structural types and within-system feedbacks linked to each vegetation type. The regional rainfall gradient did affect nutrient availability, but mainly through its effect on the relative distribution of the different vegetation structural types thus setting the range of possible outcomes of biotic interactions. 5. Synthesis. Regional and global studies that model savanna carbon and nutrient cycling only on the basis of regional gradients in soil and climatic conditions may insufficiently capture the dominant ecosystem processes involved.