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Title: Can seed-caching enhance seedling survival of Indian ricegrass (Achnatherum hymenoides) through intraspecific facilitation?

item Longland, William - Bill
item DIMITRI, LINDSAY - University Of Nevada

Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2016
Publication Date: 9/28/2016
Citation: Longland, W.S., Dimitri, L.A. 2016. Can seed-caching enhance seedling survival of Indian ricegrass (Achnatherum hymenoides) through intraspecific facilitation?. Plant Ecology. 217: 1523-1532.

Interpretive Summary: Many seed-eating small mammals bury clusters of seeds in shallow caches called “scatterhoards” and seedlings of many plant species germinate and establish tight clumps of seedlings from these caches. This is known to be the case for Indian ricegrass, a desert grass species that is an important forage source for livestock and wildlife on many aridland winter ranges. Although the vast majority of Indian ricegrass seedlings are known to originate from scatterhoards made by certain rodent species, it was unknown whether clumping of seedlings affected their subsequent survival. We conducted a field experiment to compare survival of Indian ricegrass seedlings growing singly versus those growing in clumps of either 25 or 35 seedlings. All seedlings growing singly died during the hot, dry summer months, whereas some seedlings survived in both sizes of clumps. Rather than having negative effects by simply competing with one another, clumping had a positive effect on survival of individual seedlings. Such positive effects of individual plants on others growing in close proximity (often referred to as “facilitation”) suggest that seed caching animals can benefit long-term survival of Indian ricegrass.

Technical Abstract: Positive interactions among individual plants (facilitation) may often enhance seedling survival in stressful environments. Many granivorous small mammal species cache groups of seeds for future consumption in shallowly buried scatterhoards, and seeds of many plant species germinate and establish aggregated clusters of seedlings from such caches. Scatterhoards made by desert heteromyid rodents provide a major source of seedling recruitment for Indian ricegrass (Achnatherum hymenoides), a perennial bunchgrass species occurring widely across arid southwestern deserts of North America. However, effects of the resulting clumping of seedlings on subsequent survival have not been quantified under field conditions, which include extended periods of excessive summer heat and little precipitation. We monitored Indian ricegrass seedlings transplanted into field exclosures at two western Nevada study sites as either single seedlings or clumps of 25 or 35 seedlings and compared their survival. Survival was positively correlated with the number of seedlings growing together, and survival of whole clumps of 25 or 35 seedlings was significantly greater than that of seedlings growing singly. Moreover, individual seedlings within clumps of 25 or 35 seedlings had significantly higher survival than seedlings growing singly. No single seedlings survived through the hot and very dry summer following their planting, but a small proportion (1.4 – 2.3%) of clumped seedlings survived. Results of this field experiment suggest that facilitative benefits accruing to Indian ricegrass due to seed-caching desert rodents can extend past seedling establishment and into the longer-term survival of the plant.