A mammoth mouthful? A test of the idea that larger animals ingest larger seeds

Abstract

Aim It has been widely assumed that large seeds generally require large animals to ingest and disperse them. However, this relationship has only been quantified in single animal groups (e.g. birds) and in a few communities. Our goal was to provide the first broad-scale study of the relationship between animal body mass and ingested seed size.Location Global. MethodsWe compiled a dataset of 13,135 unique animal × seed interactions, animal body masses and seed sizes in these interactions, across all vertebrate groups (fish, amphibians, reptiles, birds and mammals). ResultsContrary to expectations, ingested seed size was negatively related to animal body mass. This negative relationship was largely driven by large ungulates ingesting small and dry seeds, and analyses excluding either ungulates or seeds with non-fleshy fruit types showed a positive relationship between animal body mass and ingested seed size. Large animals ingested both seeds with a larger maximum size (the 95th quantile had a positive slope) and a smaller minimum size (the 5th quantile had a negative slope). Larger animals ingest larger seeds from fleshy fruits but smaller seeds from non-fleshy fruits. A significant positive relationship was found between animal size and the number of seed species ingested. Main conclusionsOur data show that one of the assumptions that has underpinned the study of animal-seed interactions does not hold true across the full range of animal taxa and fruit types. These findings shed new light on theories about which types of plant species might be at risk if large animals go extinct, and cast doubt on the generality of a few theories (e.g. optimal diet theory, fruit-size hypothesis) about the relationship between frugivores and seeds.

The distribution of plants and seed dispersers in response to habitat fragmentation in an artificial island archipelago

“…To further explore the explicit contribution of birds and mammals, we identified the animal‐dispersed species into mainly bird vs. mammal‐dispersed based on a comprehensive literature survey, expert enquiry, as well as field observations which included direct evidence of seeds swallowed by birds and seeds found in birds/mammals’ faeces (e.g. Chen & Moles, ) (see Appendix S2).…”

“…() concluded that small‐seeded plants may be more resilient to forest fragmentation than large‐seeded plants. However, previous studies have shown that many of the small‐seeded species were bird‐dispersed while large‐seeded species were mainly mammal‐dispersed (Chen & Moles, ; Liu et al., ). Therefore, an alternative interpretation of their results could be that bird‐dispersed plant species are more resilient to fragmentation than mammal‐dispersed species.…”

Can dispersal investment explain why tall plant species achieve longer dispersal distances than short plant species?

“…seed mass = diaspore mass), but only in those cases where the original paper specifically stated that the diaspore had no dispersal structures. These species can be dispersed by gravity, wind, water and/or animals (Willson, ; Chen & Moles, ). A thickened seed coat can aid dispersal by reducing predation loss of seeds when being carried by seed‐caching animals or in the gut of animals (Vander Wall, ; Ruxton & Schaefer, ).…”

Plants show more flesh in the tropics: variation in fruit type along latitudinal and climatic gradients

“…Fruits were classified as fleshy if they possessed conspicuous fleshy pericarps or fleshy appendages when mature (e.g. aril, thalamus, receptacle, calyx, rachis or bract or succulent pedicel); otherwise, they were classified as non‐fleshy (this functional definition is similar to that used by Willson et al , Chen and Moles ).…”