Consumption and dispersion of mesquite seeds by ruminants

Abstract

Consumption of mesquite (Prosopis glandulosa Torr. var glandulosa) fruit by ruminants is an important component of seed dispersal. Two experiments were conducted to estimate the role of livestock and wildlife in the dispersion of mesquite fruit. In Experiment 1, 3 trials were conducted to determine preference for mesquite fruit by different species of livestock, intake relative to fruit maturity, and seed survival of digestion. Cattle, sheep, and goats were offered immature (IM), mature off the tree (MT), or mature off the ground (MG) fruit to quantify intake and seed survival of digestion. Germination of seeds surviving digestion was also assessed. Experiment 2 assessed rate of pod disappearance from pastures with and without livestock grazing and attempted to quantify seed loss to wildlife. In Experiment 1, livestock consumed more (P < 0.05) mature than immature fruit; sheep and goats consumed more fruit than cattle on a body weight basis. Seed survival was greater (P < 0.05) from cattle than from sheep or goats. The number of seeds remaining intact after digestion was greater for mature fruit. Germination of seeds surviving digestion was similar (P > 0.05) to seeds that experienced natural weathering for 6 months. In Experiment 2, the presence or absence of livestock did not affect the disappearance of seeds; seeds disappeared from the ground within 3 weeks in 1999 and 5 weeks in 2000 presumably by wildlife. Deer, raccoons, skunks, bobcats, turkeys, and other birds visited plots with fresh mesquite fruit. Collectively, these results suggest that cattle readily consume and disperse viable mesquite seeds; sheep and goat consumption of mesquite fruit may reduce the number of viable seeds; and mesquite fruit may only remain on the ground for a short period of time even without livestock grazing because of consumption by wildlife.