The role of seed size in dispersal by a scatter-hoarding rodent.

Abstract

A field experiment was conducted in the Nouragues Reserve, an undisturbed lowland rain forest in French Guiana, to test possible selective pressures towards higher seed value of Carapa procera by scatter-hoarders, and to quantify survival probabilities of seeds harvested and cached by red acouchies (Myoprocta exilis). The following hypotheses were also tested: (1) large seeds are more likely to be harvested by acouchies than small seeds; (2) large seeds are harvested by acouchies more quickly than small seeds; (3) large seeds harvested by acouchies have a higher probability than small seeds to be cached rather than eaten; (4) large seeds are cached further away and in lower densities than small seeds; (5) large seeds are recovered from caches and consumed at lower rates than small seeds; and (6) large seeds have higher survival probabilities than small seeds. All seeds were removed within 1.5 days, except for three seeds, which were removed 1-2 days later, thus hypothesis 1 was not confirmed. A total of 362 seeds were located after dispersal wherein 84% was cached and relatively few seeds (16%) were eaten, which confirms hypothesis 3. The distance at which acouchy caches were found immediately after dispersal was highly variable, both within and among plots. The nearest cache was found <1 m from the plot, from which the farthest was 124 m away. Cache distance increased with seed size, as predicted by hypothesis 4. There was also great variation in spatial isolation of acouchy caches, both within and among plots. Recovery of seeds did not necessarily lead to seed consumption since many seeds were reached or were not found again. Larger seeds had a higher probability of being recached rather than eaten while consumed seeds were found much closer to the cache site than recached seeds. These results support hypothesis 5. Seed mass strongly affected the fate pathways of seeds and how long seeds were kept in stock. The ultimate probability of survival increased with seed mass, as posited by hypothesis 6.

Scatter hoarding by the Central American agouti: a test of optimal cache spacing theory

“…Also, many studies have found a positive relationship between dispersal distance and seed size (e.g. Hurly & Robertson 1987;Forget et al 1998;Jansen & Forget 2001;Jansen et al 2002, 2004, Vander Wall 2003this study). The above responses all make sense in terms of economy: seed scarcity in time or space increases the 'value-of-exchange' of seeds while seed size increases the 'value-of-use', which together determine the economic value of seeds.…”

“…Several studies have found that scatter-hoarding rodents and birds tend to cache large, more nutritious seeds further away (and thus at lower densities) than small seeds (e.g. Bossema 1979;Hurly & Robertson 1987;Forget et al 1998;Jansen & Forget 2001;Jansen et al 2002Jansen et al , 2004Vander Wall 2003;Leaver 2004; but see Brewer 2001). Jansen et al (2004) argued that the value of food to hoarders is determined not only by the nutritional content (i.e.…”

How plants manipulate the scatter-hoarding behaviour of seed-dispersing animals

“…Larger nuts and seeds are usually carried greater distances to cache sites (Hallwachs 1986;Vander Wall 1995;Jansen et al 2002Jansen et al , 2004Xiao et al 2004Xiao et al , 2005aTakahashi et al 2007;Zhang et al 2008); however, a few studies (Brewer 2001;Xiao et al 2004) have failed to observe this behaviour. Large nuts also have longer residence times in caches ( Jansen et al 2002), and large nuts often demonstrate increased fitness ( Jansen et al 2004). For example, larger Quercus serrata acorns have longer cache lifetimes and are more likely to produce seedlings in spring (Xiao et al 2004); however, this was not true for larger acorns of Quercus liaotungensis .…”

“…Both intra-and interspecifically, small seeds and nuts have a greater chance of being eaten while large seeds and nuts have a greater chance of being scatter hoarded (Forget et al 1998;Jansen et al 2002Jansen et al , 2004Xiao & Zhang 2006;Vander Wall 2008;Zhang et al 2008), although other nut traits (e.g. fat or tannin content) can alter this general pattern (Xiao & Zhang 2006;see below).…”

Evidence for cache surveillance by a scatter-hoarding rodent

“…We recorded the animal species and the exact time of seed removal for each seed (as in Jansen et al 2002Jansen et al , 2004Jansen & den Ouden 2005), and identified the individual if possible. Each seed plot was checked daily and removed seeds were located by sight or with hand-held radiotelemetry equipment (Yaesu-VR500, Cypress, CA, U.S.A.) to determine dispersal distance and seed fate.…”