Importance of animal and plant traits for fruit removal and seedling recruitment in a tropical forest

Abstract

The traits of animals and plants influence their interaction networks, but the significance of species' traits for the resulting ecosystem functions is poorly understood. A crucial ecosystem function in the tropics is seed dispersal by animals. While the importance of species' traits for structuring plant-frugivore networks is supported by a number of studies, no study has so far identified the functional traits determining the subsequent processes of fruit removal and seedling recruitment.Here, we conducted a comprehensive field study on fruit removal by frugivorous birds and seedling recruitment along an elevational gradient in the Colombian Andes. We measured morphological traits of birds (body mass, bill width, Kipp's index) and plants (plant height, crop mass, fruit width and seed mass) which we expected to be related to fruit removal and seedling recruitment. We tested 1) which bird and plant traits influence fruit removal, and 2) whether network metrics at plant species level, functional identities of frugivores (community-based mean trait values) and/or plant traits were the main determinants of seedling recruitment. We found that large-bodied bird species contributed more to fruit removal than small-bodied bird species and that small-sized fruits were more frequently removed than large-sized fruits. Small plant species and plants with heavy seeds recruited more seedlings than did large plants and plants with light seeds. Network metrics and functional identities of seed dispersers were unrelated to seedling recruitment. Our findings have two important implications. First, large birds are functionally more important than small birds in tropical seed-removal networks. Second, the detected tradeoff between fruit size and seed mass in subsequent recruitment processes suggests that the adaptability of forest plant communities to a loss of large frugivores is limited by life-history constraints. Hence, the protection of large-bodied frugivores is of primary importance for the maintenance of diverse tropical plant communities.

Phylogenetic and Functional Diversity of Fleshy-Fruited Plants Are Positively Associated with Seedling Diversity in a Tropical Montane Forest

“…Interactions between fleshy-fruited plants and frugivorous birds are influenced by morphological traits of birds and plants, which promote or constrain fruit consumption (Dehling et al, 2014b;Muñoz et al, 2017a). Here we estimated the FD of birds and plants by corresponding bird and plant traits such as bill width and fruit size, wing shape and foraging stratum and body mass and crop size (Dehling et al, 2016).…”

“…To quantify the density of adults, we also counted all adult plants independent of their fruiting stage, i.e., we recorded all shrubs with a DBH ≥ 3 cm and all trees with a DBH ≥ 20 cm in each plot. For each of these groups, we measured three morphological traits that affect the foraging behavior of frugivores and correspond to the respective bird traits for trait matching: fruit size, plant height and crop mass (Dehling et al, 2014b;Muñoz et al, 2017a). Fruits contain the seeds of a plant species.…”

“…Top-down effects of animals on seedlings are expected to be most pronounced if different animal species provide complementary contributions to seed dispersal Schleuning et al, 2015). In contrast, a high degree of animal redundancy, and a low degree of trait matching, would dilute the signal of frugivore traits on seedling diversity, e.g., because many large frugivores are able to feed on different fruit sizes (Bender et al, 2017;Muñoz et al, 2017a). It has been shown that mutualistic plant-animal interactions are influenced by bottom-up effects of plants on animal diversity (e.g., Albrecht et al, 2014), whereas top-down effects on these interactions are usually weaker .…”

“…An important trait that affects seedling recruitment is seed size (Muñoz et al, 2017a). Seed size influences seedling survival and growth, and is related to a plant's life history strategy (Westoby et al, 1996;Rees et al, 2001).…”

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

“…The forbidden links hypothesis states that not all links (i.e., interactions) in a network are realized due to constraints on the formation of some links (Vázquez, 2005). Constraints on potential links within plant-animal mutualistic networks include a wide variety of plant or animal traits, including morphological mismatch (e.g., gape width and fruit/seed size in SD mutualisms) and phenological uncoupling (e.g., asynchrony between disperser abundance and fruiting times), that prevent links between certain components of a network (Vázquez et al, 2009;Dehling et al, 2014;Muñoz et al, 2017). The influence of morphological mismatch on the temporal dynamics of SD networks should be negligible because significant change in morphology of a species on ecological timescales occurs only under extreme evolutionary pressures (see Thompson, 1998;Grant and Grant, 2006;Galetti et al, 2013).…”