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Understanding the extent to which organisms exhibit specialization when interacting with or relying on distinct aspects of their biotic and abiotic environment is a central tenet in ecology and evolution. Despite the relevance of the concept and theoretical advances, specialization has and continues to be ambiguously defined. Here we review the uses of the term ‘specialist' using as a case study the field of frugivory and seed dispersal. Our goal is to identify points of clarity and ambiguity to promote a more consistent and coherent use of specialization in plant–frugivore interactions and similar fields. Frugivory and seed dispersal research presents a good case study because specialist–generalist concepts have guided the theoretical framework of the field since its beginnings. Our analyses show that definitions of ‘specialist frugivores' have changed over time and tend to vary also depending on the studied animal taxa, such as birds, bats, or primates. At least some of the ambiguity arises from defining specialization at different scales such as evolutionary versus ecological timeframes. More critical is the finding that specialization is commonly used on frugivore species without knowledge or measure of the biological dependance of the species on specific types of fruit resources. Specifically, we found that most studies use specialization to describe fruit‐preference patterns that – unlike specialization constrained by evolution – can be variable and context‐dependent. We call for increased awareness to distinguish between contextual cases of preferential resource‐uses, from specialized interactions that limit populations and singularly define species. [ABSTRACT FROM AUTHOR]

Negative density dependence (NDD) in biotic interactions of interference such as plant–plant competition, granivory and herbivory are well-documented mechanisms that promote species' coexistence in diverse plant communities worldwide. Here, we investigated the generality of a novel type of NDD mechanism that operates through the mutualistic interactions of frugivory and seed dispersal among fruit-eating birds and plants. By sampling community-wide frugivory interactions at high spatial and temporal resolution in Pennsylvania, Puerto Rico, Peru, Brazil and Argentina, we evaluated whether interaction frequencies between birds and fruit resources occurred more often (selection), as expected, or below expectations (under-utilization) set by the relative fruit abundance of the fruit resources of each plant species. Our models considered the influence of temporal scales of fruit availability and bird phylogeny and diets, revealing that NDD characterizes frugivory across communities. Irrespective of taxa or dietary guild, birds tended to select fruits of plant species that were proportionally rare in their communities, or that became rare following phenological fluctuations, while they mostly under-utilized abundant fruit resources. Our results demonstrate that negative density-dependence in frugivore–plant interactions provides a strong equalizing mechanism for the dispersal processes of fleshy-fruited plant species in temperate and tropical communities, likely contributing to building and sustaining plant diversity. This article is part of the theme issue 'Diversitydependence of dispersal: interspecific interactions determine spatial dynamics'. [ABSTRACT FROM AUTHOR]

Summary: Mutualisms between plants and fruit‐eating animals were key to the radiation of angiosperms. Still, phylogenetic uncertainties limit our understanding of fleshy‐fruit evolution, as in the case of Solanum, a genus with remarkable fleshy‐fruit diversity, but with unresolved phylogenetic relationships.We used 1786 nuclear genes from 247 species, including 122 newly generated transcriptomes/genomes, to reconstruct the Solanum phylogeny and examine the tempo and mode of the evolution of fruit color and size.Our analysis resolved the backbone phylogeny of Solanum, providing high support for its clades. Our results pushed back the origin of Solanum to 53.1 million years ago (Ma), with most major clades diverging between 35 and 27 Ma. Evolution of Solanum fruit color and size revealed high levels of trait conservatism, where medium‐sized berries that remain green when ripe are the likely ancestral form. Our analyses revealed that fruit size and color are evolutionary correlated, where dull‐colored fruits are two times larger than black/purple and red fruits.We conclude that the strong phylogenetic conservatism shown in the color and size of Solanum fruits could limit the influences of fruit‐eating animals on fleshy‐fruit evolution. Our findings highlight the importance of phylogenetic constraints on the diversification of fleshy‐fruit functional traits. [ABSTRACT FROM AUTHOR]

The red‐footed booby (Sula sula) is one of the most common pantropical seabird species, but its populations have been declining in the Caribbean region and elsewhere. We used distance sampling from point‐counts to estimate population size of red‐footed boobies in Mona Island, Puerto Rico, USA, before and during the breeding season in 2019. We compared results from early morning and early night surveys to determine the best survey time given that many individuals are foraging at sea during the daylight hours but not at night. We also examined the suitability of drone photography to survey active nests (a measure of breeding pairs) and compared it to point count and transect survey data. Point count surveys show that an estimated 6,130 birds occupied the colony, which is more than double previous estimates for Mona Island. Our results also showed that to avoid underestimates, red‐footed booby colonies are best surveyed at night as they yield higher bird densities than daytime surveys. For the same reason, daytime photographic surveys with a drone underestimated population size compared to nighttime point‐count surveys. However, drones were more effective than ground surveys in detecting active nests, and thus breeding pairs, which provides a better estimate of the resident population of a colony. We recommend that nighttime surveys are tailored to site‐specific conditions to improve estimates of red‐footed boobies, while drones can save significant effort and time in monitoring numbers of active nests in the remote and rugged islands where red‐footed boobies typically nest. [ABSTRACT FROM AUTHOR]

Bears, Ursidae, are considered omnivores, except for giant pandas Ailuropoda melanoleuca and polar bears Ursus maritimus. However, omnivory includes a wide range of dietary variation and trophic positions, making bear dietary ecology unclear. We inferred bear trophic positions from δ15N (‰) values and examined their correlation with diets reported in the literature, including frequency of human–bear conflicts (livestock predation and crop damage incidents). Overall, 15N signatures were consistent with diet estimates. Bear species with higher 15N signatures differed more from each other, including cases of large regional intraspecific variance, than bear species with lower 15N signatures. Bear trophic position and frequency of reports of human–bear conflicts were uncorrelated, suggesting that livestock predation by bears is an opportunistic behaviour rather than a response to food availability dynamics. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The diversity of tropical forests is strongly shaped by mutualistic interactions involving plants and frugivores that disperse their seeds. However, it is little known how decreases in the diversity of frugivores can affect seed dispersal patterns, plant community composition and species' coexistence in tropical forest landscapes. Here, we investigated the effects of bird frugivore diversity on seed dispersal of rare plant species and on the magnitude of equalizing effects on the seed rain in open areas within 12 fragmented landscapes in the Brazilian Atlantic Forest. We monitored the production of bird‐dispersed seeds and bird abundance in forest fragments, and sampled the seed rain and the activity of birds attracted to experimental tree nuclei established in neighboring pastures. The activity of frugivores in tree nuclei was positively correlated with the diversity of birds recorded in nearby forest fragments, and the seed rain diversity increased with frugivore activity. The proportion of seeds dispersed more frequently than expected by chance in tree nuclei increased linearly with the species' richness of birds. The richness and abundance of active frugivores in deforested areas promoted a seed rain with evenness and diversity up to five times greater than the seed pool available in forest fragments due to the proportional increase in the dispersal of rare plant species and a concomitant proportional decrease in the dispersal of dominant fruiting plants. Furthermore, every additional bird species detected in a site was associated with a 10% increase in the equalizing effect on dispersed seeds' relative abundance. Our results show that the aggregated behavior of avian frugivore communities on deforested areas results in higher species richness in the seed rain of plant communities and underscore the urgency to reduce bird species' loss and the simplification of their communities in tropical landscapes. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of American Naturalist is the property of University of Chicago and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Applied Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Network metrics are widely used to infer the roles of mutualistic animals in plant communities and to predict the effect of species' loss. However, their empirical validation is scarce. Here we parameterized a joint species model of frugivory and seed dispersal with bird movement and foraging data from tropical and temperate communities. With this model, we investigate the effect of frugivore loss on seed rain, and compare our predictions to those of standard coextinction models and network metrics. Topological coextinction models underestimated species loss after the removal of highly linked frugivores with unique foraging behaviours. Network metrics informed about changes in seed rain quantity after frugivore loss. However, changes in seed rain composition were only predicted by partner diversity. Nestedness, closeness, and d' specialisation could not anticipate the effects of rearrangements in plant–frugivore communities following species loss. Accounting for behavioural differences among mutualists is critical to improve predictions from network models. [ABSTRACT FROM AUTHOR]