Seed Removal, Seed Predation, and Secondary Dispersal

Abstract

Many studies of postdispersal seed fate use seed removal as an index of seed predation. However, following primary seed dispersal, some seeds are transported intact by ants, dung beetles, scatter‐hoarding animals, or abiotic processes to new microsites (secondary dispersal) where germination is possible. Despite a growing realization that secondary seed dispersal can play an important role in plant recruitment, many researchers continue to use seed removal as a proxy for seed predation and are focused too intently on only the initial step of seed fate. We describe, using examples from the recent literature, how the results of some seed removal studies may have been misinterpreted, present plausible, alternative explanations for the fate of seeds in those studies, and discuss the importance of detailed studies of seed fates. Following the fates of seeds can be difficult, but such studies contribute much more to our understanding of seed dynamics and plant fitness.

Frugivore loss limits recruitment of large-seeded trees

“…For the purpose of the analysis, we assumed seeds that disappeared were killed as there are no reports of seed caching by any animals in New Zealand and we found no evidence of it (cf. [41]). Seventy per cent of B. tarairi seeds that disappeared had their tags recovered, mostly within 1 m of the tube, indicating that the seed had been consumed.…”

Tree-shrub associations in grazed woodlands: first rodents, then cattle?

“…On the one hand, such low survival percentages lead to the questioning of the effectiveness of wood mice as dispersal agent. On the other hand, even very low survival percentages are important for plant recruitment (Levey and Byrne 1993;Vander Wall et al 2005) and may add up to a considerable recruitment over time, especially for long-lived trees such as Quercus robur (Takahashi et al 2006;Gómez et al 2008). …”

“…Those studies that measured high post-dispersal predation of acorns (Li and Zhang 2003;Iida 2006), therefore questioned the effectiveness of wood mice as dispersers. In contrast, many other studies underline the importance of seed dispersal by wood mice for tree regeneration despite high predation rates, as even a tiny fraction of acorns that escapes from post-dispersal seed predation may be sufficient for a substantial tree recruitment over time (Gómez 2004;Den Ouden et al 2005;Vander Wall et al 2005;Gómez et al 2008;Smit et al 2009). …”

“…Wood mice (Apodemus sylvaticus) and Eurasian jays (Garrulus glandarius) play an important role as dispersers of acorns of pedunculate oak in woodlands (Kollmann and Schill 1996;Den Ouden et al 2005;Vander Wall et al 2005). Both animals bury large amounts of acorns during the autumn as food supply for the winter.…”

Diaspore heteromorphism in the invasive Bromus tectorum L. (Poaceae): Sterile florets increase dispersal propensity and distance

“…diaspores are first transported from the plant to a surface (primary dispersal), then surface-lying diaspores can be redistributed until they germinate, are permanently trapped or dispersal structures deteriorate (secondary dispersal) (Matlack, 1989;Schurr et al, 2005;Vander Wall et al, 2005); (3)dispersal is affected by the environment, notably the presence of obstructions that can stop diaspore movements, the vegetation structure that can modulate wind speeds, and/or the animals that can play a significant role in redistributing diaspores over the landscape (Horvitz and Schemske, 1986;Nathan and Muller-Landau, 2000). Therefore, to describe the dispersal ecology of a plant species, both primary and secondary dispersal by its different dispersal agents should be investigated in different habitats.…”