Seed Selection by Desert Rodents: Implications for Enhancing Seedling Establishment of Indian Ricegrass (Oryzopsis hymenoides)

Authors: Longland, William - Bill; DIMITRI, LINDSAY - University Of Nevada

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2016
Publication Date: 7/14/2016
Citation: Longland, W.S., Dimitri, L.A. 2016. Seed Selection by Desert Rodents: Implications for Enhancing Seedling Establishment of Indian Ricegrass (Oryzopsis hymenoides). Western North American Naturalist. 76:253-258.

Interpretive Summary: Seeds of Indian ricegrass, an important forage plant for livestock and wildlife on western desert rangelands, provide a preferred food for desert rodents, which bury clusters of the seeds in shallow deposits called scatterhoards. The plant has developed a close relationship with these animals; most new Indian ricegrass seedlings emerge from the few scatterhoards that rodents make but then fail to recover and consume. This raises the possibility of enhancing the productivity of Indian ricegrass by means of reducing the likelihood that rodents recover Indian ricegrass seeds caches, so that more of them remain in the ground to eventually produce new seedlings. This has been attempted by distributing commercial “diversionary seeds” on the soil surface during the time of year that rodents would be recovering and consuming scatterhoards, so that animals have an alternate food source that diverts their attention from recovering Indian ricegrass scatterhoards. Because the success of this strategy is likely to depend to the desirability to rodents of Indian ricegrass seeds relative to diversionary seeds, we tested for rodent preferences for Indian ricegrass versus 5 potential diversionary seed candidates. Indian ricegrass seeds were consistently preferred by captive kangaroo rats over only one of these alternate seeds. Different individual kangaroo rats showed varying preferences among the seed types, but one of the diversionary seed candidates was consumed by all animals tested in greater amounts than Indian ricegrass seeds. We therefore believe that a mixture of various diversionary seeds would be a better strategy for enhancing Indian ricegrass seedling production than a single type of diversionary seed.

Technical Abstract: Seeds of many plant species are dispersed by seed-caching rodents that place groups of seeds in superficially-buried scatterhoard caches. A case in point is provided by an important forage plant on arid western rangelands, Indian ricegrass (Oryzopsis hymenoides), for which seedling recruitment comes largely from scatterhoards made by desert heteromyid rodents. This has resulted in attempts to employ a “diversionary seeding” strategy for enhancing Indian ricegrass seedling recruitment by deploying commercially available seeds on the soil surface to divert rodents from recovering scatterhoards of Indian ricegrass seeds. The probability of such a passive restoration approach succeeding is likely to be affected by relative desirability of Indian ricegrass seeds versus diversionary seeds to rodents. We conducted laboratory experiments to test for preferences of a primary dispersal agent of Indian ricegrass seeds, Merriam’s kangaroo rat (Dipodomys merriami), for Indian ricegrass seeds versus seeds of 5 potential diversionary seed candidates. Indian ricegrass seeds were consistently preferred over only one of the 5 alternate seeds in pairwise trials. In multi-seed trials that presented all seed types (i.e., Indian ricegrass and the 5 alternates) simultaneously, ranking patterns of individual kangaroo rats varied significantly and Indian ricegrass was not preferred by any of the animals tested. Because individual kangaroo rats differed in seed preferences and all animals consumed certain seed types in greater amounts than they consumed Indian ricegrass, we suggest that using a mixture of different seed types in diversionary seedings is superior to deploying a single type of diversionary seeds. Understanding how population-level niche breadth is affected by dietary variation at level of individuals can thus have important management implications.