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What Role do Seed Eaters (Granivores) Play? Image of a rodent with an ID tag in its ear

Seed eaters are harmful...right?
Not necessarily. IFAFS researchers are studying the role these seed eaters, or granivores, play in natural and human-aided revegetation.

Besides merely eating seeds, granivores hide seed caches to be eaten later. Both rodents and ants hide seeds in deep underground caches called ‘larderhoards’. These caches are generally too deep for seeds to grow. Rodents also scatter shallowly buried seed caches (scatterhoards) throughout their home range. These ‘scatter-hoarded’ seeds are buried at about the right depth for a sprouting seedling to survive. Granivores also carry the seeds away from the parent plant enabling seed distribution. 

Picture of an exclosure built to keep rodents out

Despite the good that granivores do for plants, they can become pests during a restoration project. They collect the scattered seeds and can diminish revegetation success. This is bad news for land managers because range seedings are expensive and it is already difficult to achieve good stand establishment.

How can we discourage granivory during a revegetation project? Drill seeding buries seeds so fewer are found and eaten. This isn't possible in large areas or in rocky and steep terrain. It is also helpful, though more expensive, to plant more seeds. This ‘shotgun approach’ makes it more likely enough seeds will make it through. A less expensive variation on this idea is to include a cheaper ‘decoy’ seed in the mix that granivores prefer compared to the expensive seeds.

Images:
-Steve Ostoja

Text references:
-Archer, S., and D.A. Pyke. 1991. Plant-animal interactions affecting plant establishment and persistence on revegetated rangeland. Journal of Range Management. Vol. 44 No. 6 pp. 558-565.
-Kelrick, M.I. and J.A. MacMahon. 1985. Nutritional and physical attributes of seed and some common sagebrush steppe plants: some implications for ecological theory and management. Journal of Range Management. Vol. 38 No. 1 pp. 65-69.
-Longland, W.S., S.H. Jenkins, S.B. Vander Wall, J.A. Veech, and S. Pyare. 2001. Seedling recruitment in Oryzopsis hymenoides: Are desert granivores mutualists or predators? Ecology. Vol. 82 No. 11 pp. 3131-3148.
- Longland, W.S., and S.L. Bateman. 1998. Implications of desert rodent seed preferences for range remediation. Journal of Range Management Vol. 51 No. 6 pp. 679-684.