Interactions between resource and consumer species are organized in ecological networks. Species interactions in these networks are influenced by the functional traits of the interacting partners, but the generality of trait-based interaction rules and the relationship between functional traits and a species' specialization on specific interaction partners are not yet understood. Here we combine data on eight interaction networks between fleshy-fruited plants and frugivorous birds sampled across the tropical and subtropical Andean range. We test which combinations of morphological plant and animal traits determine trait matching between resource and consumer species in these networks. In addition, we test which of the morphological traits influence functional specialization of plant and bird species. In a meta-analysis across network-specific fourth-corner analyses, we found that plant-animal trait pairs related to size matching (fruit size-beak size) and avian foraging behavior (plant height-wing shape and crop mass-body mass) were positively related in these networks. The degree of functional specialization on specific interaction partners was positively related to crop mass in plants and to the pointedness of the wing in birds. Our findings show that morphological trait matching between fleshy-fruited plants and frugivorous birds is a general phenomenon in plant-frugivore networks across the Andes and that specific plant and bird traits can be used to approximate the degree of functional specialization. These insights into the generality of interaction rules are the base for predictions of species interactions in ecological networks, for instance in novel communities in the future, and can be applied to identify plant and animal species that fulfill specialized functional roles in ecological communities.

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Interactions between resource and consumer species result in complex ecological networks. The overall structure of these networks is often stable in space and time, but little is known about the temporal stability of the functional roles of consumer species in these networks. We used a trait-based approach to investigate whether consumers (frugivorous birds) show similar degrees of functional specialisation on resources (plants) in ecological networks across seasons. We additionally tested whether closely related bird species have similar degrees of functional specialisation and whether birds that are functionally specialised on specific resource types within a season are flexible in switching to other resource types in other seasons. We analysed four seasonal replicates of two species-rich plant-frugivore networks from the tropical Andes. To quantify fruit preferences of frugivorous birds, we projected their interactions with plants into a multidimensional plant trait space. To measure functional specialisation of birds, we calculated a species' functional niche breadth (the extent of seasonal plant trait space utilised by a particular bird) and functional originality (the extent to which a bird species' fruit preference functionally differs from those of other species in a seasonal network). We additionally calculated functional flexibility, i.e. the ability of bird species to change their fruit preference across seasons in response to variation in plant resources. Functional specialisation of bird species varied more among species than across seasons, and phylogenetically similar bird species showed similar degrees of functional niche breadth (phylogenetic signal λ = 0·81) and functional originality (λ = 0·89). Additionally, we found that birds with high functional flexibility across seasons had narrow functional niche breadth and high functional originality per season, suggesting that birds that are seasonally specialised on particular resources are most flexible in switching to other fruit resources across seasons. The high flexibility of functionally specialised bird species to switch seasonally to other resources challenges the view that consumer species rely on functionally similar resources throughout the year. This flexibility of consumer species may be an important, but widely neglected mechanism that could potentially stabilise consumer-resource networks in response to human disturbance and environmental change.

Summary 1.Restoration activities aiming at increasing vegetation diversity often try to stimulate both dispersal and germination. In wetlands, dispersal and germination are coupled as water and water level fluctuations (WLF) simultaneously influence seed transport and germination conditions (soil moisture). Water regime shifts have been shown to affect vegetation composition. However, the interactions between WLF, dispersal and subsequent germination as drivers of such changes are still poorly understood, especially within the complexity of a field situation. 2. We tested the effect of soil moisture on ten riparian species in the greenhouse and sowed these species on 135 field locations in nine wetlands with recently restored WLF. We used quantile regressions to test the effects of WLF on the window of opportunity for germination from sown seeds and other seeds naturally dispersed to our plots, as well as on community diversity. 3. Soil moisture significantly affected germination both in the greenhouse and in the field. In the complexity of a field situation, a flooding depth just below the soil level, an intermediate flooding duration and a high flooding frequency provided the best opportunities for maximal germination. This was because these conditions enhanced germination from the seed bank as well as increasing germination from dispersed seeds. Seedling diversity showed identical patterns. 4. Other known (i.e., light conditions) and unknown factors played a role as we found low and variable germination, even under optimal conditions. We found evidence that WLF can affect vegetation zonation as flooded seedling communities contained more species with high moisture affinity. 5. Synthesis and applications. Water level fluctuations provide clear windows of opportunity for germination both from the seed bank and from dispersed seeds. Water regime changes are therefore likely to strongly affect recruitment opportunities and subsequent community assembly in riparian ecosystems, for instance through climate change or management. Water level fluctuations can be used as management tool to stimulate plant recruitment and seedling diversity in riparian wetlands.

Species differ in their resource use and their interactions with other species and, consequently, they fulfil different functional roles in ecological processes. Species with specialized functional roles (specialists) are considered important for communities because they often interact with species with which few other species interact, thereby contributing complementary functional roles to ecological processes. However, the contribution of specialists could be low if they only interact with a small range of interaction partners. In contrast, species with unspecialized functional roles (generalists) often do not fulfil complementary roles but their contribution to ecological processes could be high because they interact with a large range of species. To investigate the importance of the functional roles of specialists versus generalists, we tested the relationship between species' degree of specialization and their contribution to functional‐role diversity for frugivorous birds in Andean seed‐dispersal networks. We used two measures for the specialization of birds—one based on the size, and one based on the position of their interaction niche—and measured their effect on the birds' contribution to functional‐role diversity and their functional complementarity, a measure of how much a species' functional role is complementary to those of the other species. In all networks, there were similar log‐normal distributions of species' contributions to functional‐role diversity and functional complementarity. Contribution to functional‐role diversity and functional complementarity increased with both increasing niche‐position specialization and increasing niche size, indicating that the composition of functional roles in the networks was determined by an interplay between specialization and generalization. There was a negative interaction between niche‐position specialization and niche size in both models, which showed that the positive effect of niche‐position specialization on functional‐role diversity and functional complementarity was stronger for species with a small niche size, and vice versa. Our results show that there is a continuum from specialized to generalized functional roles in species communities, and that both specialists and generalists fulfil important functional roles in ecological processes. Combining interaction networks with functional traits, as exemplified in this study, provides insight into the importance of an interplay of redundancy and complementarity in species' functional roles for ecosystem functioning. A free Plain‐Language Summary can be found within the Supporting Information of this article.

2020. Similar composition of functional roles in Andean seed-dispersal networks, despite high species and interaction turnover. Ecology 101(7):Abstract. The species composition of local communities varies in space, and its similarity generally decreases with increasing geographic distance between communities, a phenomenon known as distance decay of similarity. It is, however, not known how changes in local species composition affect ecological processes, that is, whether they lead to differences in the local composition of species' functional roles. We studied eight seed-dispersal networks along the South American Andes and compared them with regard to their species composition and their composition of functional roles. We tested (1) if changes in bird species composition lead to changes in the composition of bird functional roles, and (2) if the similarity in species composition and functional-role composition decreased with increasing geographic distance between the networks. We also used cluster analysis to (3) identify bird species with similar roles across all networks based on the similarity in the plants they consume, (i) considering only the species identity of the plants and (ii) considering the functional traits of the plants. Despite strong changes in species composition, the networks along the Andes showed similar composition of functional roles. (1) Changes in species composition generally did not lead to changes in the composition of functional roles.(2) Similarity in species composition, but not functional-role composition, decreased with increasing geographic distance between the networks. (3) The cluster analysis considering the functional traits of plants identified bird species with similar functional roles across all networks. The similarity in functional roles despite the high species turnover suggests that the ecological process of seed dispersal is organized similarly along the Andes, with similar functional roles fulfilled locally by different sets of species. The high species turnover, relative to functional turnover, also indicates that a large number of bird species are needed to maintain the seed-dispersal process along the Andes.

Aim: Species in ecological communities are linked by biotic interactions. It is therefore important to simultaneously study the impacts of global warming on interdependent taxa from different trophic levels. Here, we quantify current and potential future associations of functional diversity (based on multiple traits) and functional identity (based on individual traits) between interacting taxa using projection models under climate change. Location: A tropical elevational gradient (500-3,500 m a.s.l.) in the Manú biosphere reserve, south-east Peru. Methods: We investigated different scenarios of how species' elevational ranges might change under climate change based on projected future increases in mean annual temperature and current associations of species' elevational ranges with temperature. We computed the functional diversity and identity of current and potential future plant and bird communities based on morphological traits that have been shown to be important for plant-frugivore interactions. Finally, we tested for changes in the associations between projected functional diversity and identity of future plant and bird communities. Results: Projected functional diversity of plants and birds decreased under range contraction and range shift scenarios at low elevations. At mid-and high elevations, functional diversity of both species groups increased most strongly under range expansion. Correspondence between plant and bird functional diversity was weakest under range contraction, while it remained strong under range expansion and shift.Similarly, the correspondence of projected plant and bird functional identity was weakest under a range contraction scenario. Main conclusions:Our findings suggest that a scenario in which species are dispersal-limited and sensitive to increasing temperatures is likely to cause a functional mismatch between plant and bird communities along this tropical elevational gradient.This implies that certain functional types of plants could miss avian seed dispersers in | 1363 NOWAK et Al.

Climate change forces many species to move their ranges to higher latitudes or elevations. Resulting immigration or emigration of species might lead to functional changes, e.g., in the trait distribution and composition of ecological assemblages. Here, we combined approaches from biogeography (species distribution models; SDMs) and community ecology (functional diversity) to investigate potential effects of climate-driven range changes on frugivorous bird assemblages along a 3000 m elevational gradient in the tropical Andes. We used SDMs to model current and projected future occurrence probabilities of frugivorous bird species from the lowlands to the tree line. SDM-derived probabilities of occurrence were combined with traits relevant for seed dispersal of fleshy-fruited plants to calculate functional dispersion (FDis; a measure of functional diversity) for current and future bird assemblages. Comparisons of FDis between current and projected future assemblages showed consistent results across four dispersal scenarios, five climate models and two representative concentration pathways. Projections indicated a decrease of FDis in the lowlands, an increase of FDis at lower mid-elevations and little changes at high elevations. This suggests that functional dispersion responds differently to global warming at different elevational levels, likely modifying avian seed dispersal functions and plant regeneration in forest ecosystems along tropical mountains.