Dispersal of non-native plants by introduced bison in an island ecosystem

Abstract

An understanding of the mechanisms of seed dispersal is critical to effectively managing populations of non-native plants. We investigated whether introduced bison on Santa Catalina Island, California, have the potential to spread non-native plants through the shedding of clumps of seed-laden hair and/or ingesting and later excreting seeds. We collected clumps of hair shaved from bison during a roundup and dislodged by wallowing activity. Greenhouse and field trials were used to test for seed viability and persistence of hair clumps in wallows. In addition to trials with bison hair, we collected samples of bison dung and tested for seed germination in a greenhouse. The majority of seeds extracted from bison hair clumps were of non-native forbs. There was a significant positive relationship between the size of hair clumps and the number of seeds extracted from the clumps, suggesting that managing the introduced bison population at a lower level will help minimize the spread of non-native plants by the species. Seeds of non-native plants were capable of germinating under conditions similar to those on Santa Catalina Island. Clumps of bison hair persisted in wallows, but did not remain intact and lost nearly 40% of their original mass. The number of germinable seeds contained in bison dung was low: 18 seeds germinated from 6 of 18 dung samples. Introduced bison appear to facilitate the dispersal of non-native plants over native plants on Santa Catalina Island. Our study suggests that a comprehensive strategy to control non-native plants must involve the management of the animal agents of plant dispersal.

The dispersal of vascular plants in a forest mosaic by a guild of mammalian herbivores

“…As possible competitors to C. capreolus (Hemami et al 2005), with a smaller home range (Chapman et al 1993), increased M. reevesi numbers may result in a reduction of the total number of seeds dispersed by deer, the number of seeds deposited in restock stands and the long-distance dispersal of seeds. In contrast to other studies on introduced species (Bourgeois et al 2005;Constible et al 2005), M. reevesi are not an exclusive means of dispersal for any plant species; in fact, the role of M. reevesi was largely redundant, with 71% of species recorded from M. reevesi samples also recorded in C. capreolus.…”

Testing the potential seed availability in dung samples: comparison of two seedling emergence methods

“…The material was air-dried at room temperature (e.g. Constible et al, 2005;Eichberg et al, 2006;Malo and Sua´rez, 1995). Faeces dry up under field conditions as well; therefore this treatment simulates the natural conditions of the seeds (Malo and Sua´rez, 1995).…”

Linking abundances of the dung fungus Sporormiella to the density of bison: implications for assessing grazing by megaherbivores in palaeorecords

“…There has been a growing interest in understanding the cascading effects of these extinctions despite the challenge that the signature of herbivory and other species interactions is usually indirect in palaeorecords (Johnson 2009). Our understanding of megaherbivory as an ecological process is mostly based on contemporary experimental manipulations (Hester et al 2000;Asner et al 2009) or the post hoc assessment of the effects of local extirpations or management practices (Constible et al 2005;ter Beest 2006). Recently, the use of coprophilous fungi as indicators of palaeoherbivory in sedimentary archives has led to significant advances in our understanding of the ecological legacy -and consequences of the loss -of megaherbivores throughout the late Quaternary.…”