Changes in seed dispersal processes and the potential for between‐patch connectivity for an arid land daisy

Abstract

Abstract. Dispersal is a major and critical process in population biology that has been particularly challenging to study. Animals can have major roles in seed dispersal even in species that do not appear specifically adapted to animal-aided dispersal. This can occur by two processes: direct movement of diaspores by animals and modification of landscape characteristics by animals in ways that greatly influence dispersal. We exploited the production of large, persistent dispersal structures (seed heads, henceforth) by Erodiophyllum elderi (Asteraceae), a daisy from arid Australia, to further understand secondary dispersal. Seed head dispersal on and off animal tracks in eight E. elderi patches was monitored for 9.5 months by periodically recording the location of marked seed heads. Sites were located inside a reserve that excludes sheep but not kangaroos, and in a nearby area with both kangaroos and sheep. The distance moved and likelihood of seed head movement was higher in areas with sheep, and especially along animal tracks. There was clear evidence that seed heads were channeled down animal tracks during large rainfall events. Seed head dispersal away from patches occurred to a limited extent via their physical contact with sheep and potentially via wind dispersal. Thus, the advantages of this study system allowed us to demonstrate the two postulated effects of herbivores on dispersal via direct movement of seed heads, and two distinct indirect effects through landscape modification by herbivores from the creation of animal tracks and the denudation of vegetation.

The fate of seeds in the soil: a review of the influence of overland flow on seed removal and its consequences for the vegetation of arid and semiarid patchy ecosystems

“…These studies highlight the absence of seed movement from the bare interpatch areas to the vegetation patches in combination with a low seed trapping capacity by the vegetation (Aerts et al, 2006) or with short dispersal distances relative to the pattern of spatial heterogeneity (Venable et al, 2008;Emmerson et al, 2010Emmerson et al, , 2012. The authors concluded that successful recruitment of the species used in these experiments could not rely on seed transport by runoff but depended on other mechanisms such as primary dispersal (Aerts et al, 2006) or the temporal delay of germination (Venable et al, 2008;Siewert and Tielborger, 2010).…”

“…Sala, 1997, 1999;Schurr et al, 2004;Puigdefábregas, 2005;Aerts et al, 2006;Saco et al, 2007;Venable et al, 2008;Emmerson et al, 2012;Thompson et al, 2014). Figure 5 illustrates schematically these implications on the basis of the available literature described hereafter.…”

Long‐term influence of fallen logs on patch formation and their effects under contrasting grazing regimes

“…They found dispersal to be greatly limited inside the reserve with maximum distances recorded to be just over a metre, while seed heads were more likely to move farther outside the reserve in paddocks subject to sheep grazing, especially along animal tracks (Emmerson et al . ). A greater mobilization of seeds in the grazed paddock could result in seeds moving further before being trapped in a patch, or even potentially being lost from the paddock.…”

“…Studies by Emmerson et al . (, ) have shown that seeds are also subject to this movement and subsequent deposition in the landscape. However, few studies have looked at patch formation over long time frames.…”

Peer Review #2 of "Herbivore corridors sustain genetic footprint in plant populations: a case for Spanish drove roads (v0.2)"

“…While the ecological importance of large wild herbivores is practically disappearing at the global scale (Ripple et al 2014;Smith & Botha-Brink 2014;Bar-On et al 2018), as are the migratory systems they support (Berger 2004), domestic herbivores have largely overtaken their role to the point that they can even substitute extinct megaherbivores (Pires et al 2014). The effectiveness of livestock seed dispersal as a cheap and effective management tool for increasing connectivity between isolated grassland habitat patches has been extensively surveyed (Cosyns et al 2005;Couvreur et al 2005;Auffret et al 2012;Emmerson et al 2012), showing that the complementarity between different modes of dispersal (endo-and epizoochory) can lead to an almost complete representation of the grassland community in the dispersal spectra (Couvreur et al 2005). Herbivory, trampling and nutrient redistribution by livestock also generate microsites favorable to the recruitment of many adapted species (Bullock et al 1994, Olff & Ritchie, 1998, contributing to functional connectivity.…”