Small‐mammal seed predation limits the recruitment and abundance of two perennial grassland forbs

Abstract

Although post-dispersal seed predators are common and often reduce seed density, their influence on plant population abundance remains unclear. On the one hand, increasing evidence suggests that many plant populations are seed limited, implying that seed predators could reduce plant abundance. On the other hand,.it is generally uncertain whether the magnitude of seed limitation imposed by granivores is strong enough to overcome density-dependent processes that could compensate for seed loss at later stages. We examined the impact of seed predation by small mammals, primarily deer mice (Peromyscus maniculatus), on seedling recruitment and subsequent plant establishment of two perennial grassland forbs in western Montana, USA: Lupinus sericeus (Fabaceae) and Lithospermum ruderale (Boraginaceae). The experiment combined graded densities of seed addition for each species with a small-mammal exclusion treatment. Seedling recruitment and plant establishment were monitored in the experimental plots for up to three years. For both species, small-mammal exclusion increased the total number of seedlings that emerged, and these effects were still significant three years after seed addition, resulting in greater numbers of established plants inside exclosures than in control plots. We also found evidence of seed limitation, with increasing density of seeds added leading to increased numbers of seedlings. Results from seed addition and small-mammal exclusion experiments in later years also revealed significant impacts of small mammals on seedling emergence. These results suggest that granivores can have potentially important impacts in limiting forb abundance in grasslands communities.

Seed fate and seedling dynamics after masting in two African rain forest trees

“…Hulme (1998) commented that few studies had quantified predation from multiple guilds of seed predators, particularly in the tropics, and in general the dearth of field experiments that also monitored subsequent seedling dynamics (e.g., Schupp and Fuentes 1995, Curran and Webb 2000, Bricker et al 2010. At Korup we demonstrated that Microberlinia died faster than Tetraberlinia, and both species survived best when protected from small mammals in gaps (Fig.…”

“…Invertebrate predation, however, did not fully offset increased seedling establishment of Microberlinia in exclosures. Not unlike forbs in grasslands (Bricker et al 2010 [Green and Newbery 2002]). A similar ''enemy-replacement'' phenomenon, but greater in severity, was reported from another African rain forest where 84% of mast seeds of the mono-dominant Gilbertiodendron dewevrei (Caesalpiniaceae) protected against small mammals were killed by specialist curculionid beetles (Hart 1995;also see Hall 2008).…”

“…The impact on species abundance is expected to be greater for species that are more strongly limited by seed than microsite availability (Harper 1977, Crawley 1989. Although the four factors are clearly not mutually exclusive, more often than not they have been studied separately; very rarely for instance has seed germination and seedling establishment been followed after controlling for seed predation and microsite features (Schupp and Fuentes 1995, Hulme 1998, Hulme and Kollmann 2005; but see Howe and Brown 2001, Paine and Beck 2007, Bricker et al 2010. A further little-studied dimension is the extent to which seeds are affected by pathogens (Watt 1919, Dalling et al 1998.…”

Biogeographic Events Are Not Correlated with Diaspore Dispersal Modes in Boraginaceae

“…Some further examples of epizoochory are found in the genera Lappula (Ridley, 1930) and Cryptantha, the latter possessing small nutlets and rough sculpturing, which are easily detached from the plant (Carlquist, 1983;Grau, 1983;Hasenstab-Lehman and Simpson, 2012). Endozoochory is typical in Lithospermum L., whose stone-like nutlets are swallowed by granivorous birds, passing intact through their guts and germinating successfully later on (Van der Pijl, 1982;Best and Smartt, 1986;Bricker et al, 2010;Selvi et al, 2011;Weigend et al, 2016). In this genus the occurrence of barochory has also been shown (Selvi et al, 2011).…”

Native Small Mammal Use of an Invasive Grass: Heermann's kangaroo rats (Dipodomys heermanni) and Veldt grass (Ehrharta calycina) in Coastal California

“…In a study examining the effect of post-dispersal seed predation on two perennial forbs in a grassland, granivores such as Peromyscus maniculatus, were found to be the primary driver for differences in plant abundance in and out of small mammal exclosures (Bricker et al, 2010). The granivores were able to lower the plant abundance outside of the small mammal exclosures in this grassland habitat, which adds to similar work in desert and coastal dunes systems (Bricker et al, 2010).…”