Spotted Knapweed Seed Viability after Passing through Sheep and Mule Deer

Abstract

Spotted knapweed (Centaureu maculosa Lam.), an introduced perennial plant, has invaded large areas of rangeland in the northwestern United States. Grazing animals may disseminate the weed by transporting seeds in their digestive system and depositing them in their feces. In this study percent viability and emergence of spotted hnapweed seeds that passed through mule deer (Odocoileus hemionus hemionus) and sheep (Ovis aries) were determined. Percent viability included seeds that germinated and seeds that tested positive with tetrazoiium. In the first trial, we pulse dosed 3 mule deer and 4 ewes with 5,000 spotted knapweed seeds each. Seed recovered from manure collected daily for 10 days after dosing was tested for percent viability. We recovered 11% of the knapweed seeds from the 3 mule deer, and 4% from the sheep. Based on high variability in (0 to 26%) percent viability of recovered seed, we thought that our drying the manure at 50°C may have hilled some of the spotted knapweed embryos. To determine if drying at 50°C affected viability, we pulse dosed 4 rams with 5,000 spotted knapweed seeds each in a second trial. One subsample of manure was washed the same day to recover seeds and then dried at 3S'C, a second subsample was dried at 50°C, washed, and then dried at 3S'C. We recovered 17% of the spotted knapweed seeds from the 4 rams. No viable seeds were recovered from manure heated at 50°C, and no viable seeds were recovered more than 2 days after dosing. Percent viability of seeds recovered from manure dried at 35°C ranged from 0 to 22%. In both trials, percent viability of recovered seeds was lower compared with seeds that did not pass through animals. Sheep and mule deer can ingest, transport, and disseminate viable seeds of spotted hnapweed in their feces.

Biodiversity, exotic plant species, and herbivory: The good, the bad, and the ungulate

“…Invasive plant seeds have been recovered from feces and found viable in numerous studies (Thill et al, 1986;Wallander et al, 1995;Malo et al, 2000;Olson and Wallander, 2002). Malo et al (2000) concluded that the effect of seed input to the seed bank from ungulate transport may be low at large and medium-sized spatial scales, but very important at small scales and for colonization processes.…”

Recovery of Leafy Spurge Seed from Sheep

“…In the past, numerous plant species were introduced to Europe via sheep fleeces (Ridley 1930 Sheep consuming leafy spurge seeds may also disperse viable seeds in their feces (Harmon and Keim 1934, Lehrer and Tisdale 1956, Özer 1979, Thill et al 1986, Simao Neto et al 1987, Dastgheib 1989. Viability of seed recovered from feces may be enhanced or reduced compared with seed that has not passed through sheep (Harmon and Keim 1934, Lacey et al 1992, Wallander et al 1995. Germinability of seeds recovered from feces generally decreases as residence time in the gastrointestinal tract of sheep increases (Özer 1979, Lacey et al 1992, Wallander et al 1995.…”

“…Viability of seed recovered from feces may be enhanced or reduced compared with seed that has not passed through sheep (Harmon and Keim 1934, Lacey et al 1992, Wallander et al 1995. Germinability of seeds recovered from feces generally decreases as residence time in the gastrointestinal tract of sheep increases (Özer 1979, Lacey et al 1992, Wallander et al 1995.…”

Do ungulates facilitate native and exotic plant spread?

“…This is particularly surprising because native and introduce ungulates dominate most western US landscapes. Viable seeds of invasive plants have been recovered from dung in several studies, but data are limited to a small handful of species including leafy spurge (Euphorbia esula), common crupina (Crupina vulgaris), spotted knapweed (Centaurea maculosa), and Lehmann lovegrass (Eragrostis lehmanniana) (Fredrickson et al, 1997;Olson et al, 1997;Wallander et al, 1995).…”