The important role of animal social status in vertebrate seed dispersal

Abstract

Seed dispersal directly affects plant establishment, gene flow and fitness.Understanding patterns in seed dispersal is, therefore, fundamental to understanding plant ecology and evolution, as well as addressing challenges of extinction and global change. Our ability to understand dispersal is limited because seeds may be dispersed by multiple agents, and the effectiveness of these agents can be highly variable both among and within species. We provide a novel framework that links seed dispersal to animal social status, a key component of behaviour. Because social status affects individual resource access and movement, it provides a critical link to two factors that determine seed dispersal: the quantity of seeds dispersed and the spatial patterns of dispersal. Social status may have unappreciated effects on post-dispersal seed survival and recruitment when social status affects individual habitat use. Hence, environmental changes, such as selective harvesting and urbanisation, that affect animal social structure may have unappreciated consequences for seed dispersal. This framework highlights these exciting new hypotheses linking environmental change, social structure and seed dispersal. By outlining experimental approaches to test these hypotheses, we hope to facilitate studies across a wide diversity of plant-animal networks, which may uncover emerging hotspots or significant declines in seed dispersal.

Long-term, large-scale experiment reveals the effects of seed limitation, climate, and anthropogenic disturbance on restoration of plant communities in a biodiversity hotspot

“…In revealing that the arrival of viable seeds can yield long-term increases in diversity, our results suggest that factors affecting the potential for long-distance dispersal of plants will be essential for promoting plant biodiversity under global change ( 29 – 31 ). For example, conservation strategies that increase dispersal via passive means, such as conservation corridors ( 30 ), activities that lead to large changes in seed production (e.g., canopy thinning) ( 44 ), or changes in the behavior of seed-dispersing animals ( 29 ) may have promoted persistent plant populations by increasing rates of establishment. As we describe below, our study indicates seed dispersal is necessary, but not always sufficient: the success of long-distance dispersal events depends not only on seed input, but on postdispersal climatic conditions and site-level management activities.…”

“…It is important to understand if one (or more) of these stages is limiting diversity because limitation can happen at any of these bottlenecks (e.g., while establishment is needed for persistence, persistence is never guaranteed) and because different forms of limitation often require different restoration approaches. For example, if plant diversity is only limited by the dispersal of seeds into areas where species have been eliminated by past human land uses ( 25 – 28 ), then adding seeds [or otherwise facilitating long-distance dispersal ( 29 – 31 )] will ensure restoration success. However, if granivores destroy arriving seeds before they establish ( 32 ), then restoration aimed at reducing seed palatability or satiating granivores will be important (e.g., ref.…”

Channel Island Foxes (Urocyon littoralis) are Viable Seed Dispersal Agents of Toyon (Heteromeles arbutifolia)

“…Since we collected scat in an area estimated to contain at least 35 individual foxes (unpublished NPS data), we expect that the majority of our independent scat samples came from distinct individuals. It is therefore possible that between-sample variation in seed germination may reflect individual-level variation in seed dispersal quality by island foxes (Zwolak 2018, Zwolak and Sih 2020, Bartel and Orrock 2022). For example, scat samples with low probabilities of seed germination may have been deposited by individual foxes that consumed and hence digested greater amounts of unripened berries with seeds that were not fully mature.…”

“…For example, scat samples with low probabilities of seed germination may have been deposited by individual foxes that consumed and hence digested greater amounts of unripened berries with seeds that were not fully mature. It is possible that socially subordinate foxes consume greater amounts of unripened berries if ripened berries are readily depleted by socially dominant foxes (Bartel and Orrock 2022). Moreover, an individual fox's size and diet can affect gut retention time, which may be a source of variation in seed germination between scat samples (Zwolak 2018, Zwolak and Sih 2020).…”

“…The island fox is highly omnivorous and often relies heavily on plant material, with 20%-40% of the annual diet containing fruit material (Crooks and Van Vuren 1995, Moore and Collins 1995, Cypher et al 2014). This substantial reliance on fruit suggests that the island fox has the potential to play an important role in dispersing seeds, a role that may be further modified by significant changes in fox abundance and behavior generated by changes in introduced species, resource availability, and social interactions (Delibes-Mateos et al 2008, Selwyn et al 2020, Bartel and Orrock 2022, Burgos et al 2022. Although the only published research (to our knowledge) evaluating seed dispersal by terrestrial vertebrates on the Channel Islands documented secondary seed dispersal by scatter-hoarding Island Scrub-Jays (Aphelocoma canabis; Pesendorfer et al 2016Pesendorfer et al , 2018, there are a number of omnivorous bird species that consume fleshy fruit on the Channel Islands and may also be agents of seed dispersal (e.g., Callipepla californica, Catharus guttatus, Ixoreus naevius, Turdus migratorius, Mimus polyglottos, Sturnus vulgaris, Bombycilla cedrorum, and Pipilo maculatus ;Beal 1907a, 1907b, Bent 1949, Collins 2011.…”