Gophers and grassland: a model of vegetation response to patchy soil disturbance

Hobbs, Richard J.; Hobbs, V. J.

doi:10.1007/bf00038695

Cited by 56 publications

(20 citation statements)

References 15 publications

(15 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Mean annual rainfall over the 35-year period of 1967-2002 is 658 mm, varying greatly among years, from 207 to 1334 mm (Jasper Ridge Biological Preserve, unpublished data). The vegetation on the serpentine and adjacent nonserpentine soils has been described by McNaughton (1968) and studied in detail by Hobbs and Mooney (1985, 1991 and Hobbs and Hobbs (1987). The serpentine grassland is dominated by native annual forbs, but native bunch grasses and geophytes are also typically present.…”

Section: Study Sitementioning

confidence: 99%

“…This is further reinforced when one considers attempts to model the dynamics of the serpentine grassland based on short-term observations. Attempts to model the spatial and temporal dynamics of the grassland in relation to disturbance (e.g., Hobbs and Hobbs 1987, Moloney et al 1992, Wu and Levin 1994, Moloney and Levin 1996 have all been based on the plant population parameters derived from a short-term study conducted during 1983-1984(Hobbs and Mooney 1985. As has been indicated above, the grassland composition during that period has not been replicated again over the 20year study and one of the key species modeled, Bromus hordeaceus, was mostly absent from the study plots for several of the study years.…”

Section: Value Of the Long-term Data Setmentioning

confidence: 99%

See 1 more Smart Citation

Long-Term Data Reveal Complex Dynamics in Grassland in Relation to Climate and Disturbance

Hobbs

Yates

Mooney

2007

Ecological Monographs

129

View full text Add to dashboard Cite

We conducted a long‐term experiment in grassland with the aim of elucidating grassland dynamics in relation to variations in rainfall amount and spatial and temporal variation in disturbance. In particular we aimed to increase our understanding of ecosystem dynamics and function, species redundancy, invasion biology, and other related topics. We studied the dynamics of serpentine annual grassland in northern California over the period 1983–2002 in a replicated series of experimental plots comprising controls, gopher exclosures, and aboveground herbivore exclosures. Annual rainfall amount varied greatly during the study period, which included two major El Niño events and a period of prolonged below‐average rainfall. Gopher disturbance was highly variable both spatially and temporally but was positively correlated with soil depth. Disturbance was reduced but not eliminated from the gopher exclosures and was significantly increased in the aboveground herbivore exclosures. Grassland dynamics were driven by rainfall amounts and distributions that had the most pronounced effects on the dominant plant species, while gopher disturbance had additional effects on the rarer species. Effects of excluding aboveground herbivores were swamped by a large increase in gopher disturbance within aboveground exclosures. Overall species numbers were reduced during a period of below‐average rainfall but recovered in subsequent years. There was a large array of different responses of individual plant species to both rainfall and disturbance. Our results provide support for the “insurance” hypothesis, which suggests that biodiversity buffers ecosystem processes against environmental changes because different species (or phenotypes) respond differently to these changes, leading to functional compensations among species. Here, a species that was at very low abundance levels at the start of the study (Microseris douglasii) temporarily increased in abundance to become one of the dominant species in the grassland following a period of prolonged below‐average rainfall. We also observed the repeated invasion of the serpentine grassland by the nonnative grass Bromus hordeaceus, which increased greatly in abundance following both of the major El Niño events. The results emphasize the importance of long‐term observations in providing a context for shorter‐term studies and allowing analysis of plant community responses to climate variation and disturbance, particularly in the face of ongoing global change.

show abstract

Section: Study Sitementioning

confidence: 99%

Section: Value Of the Long-term Data Setmentioning

confidence: 99%

Long-Term Data Reveal Complex Dynamics in Grassland in Relation to Climate and Disturbance

Hobbs

Yates

Mooney

2007

Ecological Monographs

129

View full text Add to dashboard Cite

show abstract

“…In the absence of gopher disturbance, grasslands often become dominated by perennial grasses. The soil tailings that pocket gophers deposit on the soil surface while constructing foraging tunnels increase the abundance of annual plants, their preferred food (Laycock 1958, Mc-Donough 1974, Tilman 1983, Hobbs and Mooney 1985, Hobbs and Hobbs 1987, Inouye et al 1987, Peart 1989, Hunt 1993, Davis et al 1995, Kitajima and Tilman 1996. Pocket gophers' reliance on annual forbs is strong enough that using an herbicide to eliminate forbs from a Colorado grassland reduced pocket gopher populations up to 90% due to starvation (Keith et al 1959, Ward and Keith 1962, Tietjen et al 1967, Tietjen 1973.…”

Section: Introductionmentioning

confidence: 99%

Multiple Stable Equilibria in Grasslands Mediated by Herbivore Population Dynamics and Foraging Behavior

Seabloom

Richards

2003

Ecology

View full text Add to dashboard Cite

Plant community structure is often the result of interactions between succession, disturbance, and dispersal. While some disturbances may be highly stochastic (e.g., flooding or landslides), other types of disturbance are closely linked to the current successional state of the community (e.g., fire or herbivory). For example, when herbivores preferentially feed on early successional species they may generate conditions favorable for these species and thus create a positive feedback. Positive feedbacks may create multiple stable equilibria within plant communities. We demonstrate the presence of these positive feedbacks using experiments conducted in a restored California grassland. We found that pocket gophers (Thomomys bottae) preferentially forage in areas dominated by annual species, and gopher foraging activity increases the abundance of annual plants. We use a Markov chain model to identify how the foraging behavior, dispersal behavior, and population dynamics of territorial herbivores can structure a plant community across multiple spatial scales. The model is loosely based on the biology of pocket gophers, though it is general enough to be applicable to other territorial herbivores with foraging preferences. We find that a foraging preference for early successional species can generate multiple plant communities that persist within a herbivore's territory. If juveniles are selective when searching for territories during their dispersal phase, then herbivores can also generate persistent and distinct plant communities over larger spatial scales. In this case, fixed regions of the landscape may become occupied by herbivores for long periods (many herbivore generations) and be composed of a range of successional plant species, whereas the remaining landscape is abandoned by herbivores and becomes dominated by late successional species. This structuring of the landscape occurs even though we assume that the entire landscape is intrinsically identical.

show abstract

“…It is clear that disturbance can alter plant community composition and diversity (see reviews by Pickett and White [1985], Petraitis et al [1989]), but the mechanisms responsible for the changes have rarely been tested. The most common explanation for these changes is competitive reduction: disturbance reduces competitive intensity by either removing the competitively dominant species or simply reducing density overall, allowing competitively inferior ''fugitive'' species to persist because they are better able to rapidly colonize gaps (Levins and Culver 1971, Horn and Peart and Foin 1985, Belsky 1986b, Hobbs and Hobbs 1987, Hobbs and Mooney 1991, Tilman and Pacala 1993, Tilman 1994Fig. 1A).…”

Section: Introductionmentioning

confidence: 99%

Do Disturbances Alter Competitive Hierarchies? Mechanisms of Change Following Gap Creation

Suding

Goldberg

2001

Ecology

View full text Add to dashboard Cite

Many studies have documented that patterns of species composition change after gap creation, but few have addressed the processes responsible for this change. The idea of competitive reduction, that disturbance removes biomass, reducing competitive intensity and allowing competitively inferior fugitive species to colonize, has been widely accepted but rarely tested. We suggest an alternative hypothesis, competitive change, in which changes associated with disturbance may act to alter the competitive hierarchy. Under these changed conditions, species characteristic of gaps may be competitively superior to species characteristic of undisturbed matrix areas. We quantified competitive response ability for survival and relative growth for three target species (Andropogon gerardii, a matrix grass; Coreopsis tripteris, a matrix forb; and Ratibida pinnata, a forb characteristic of gaps) in undisturbed matrix vegetation and in soil mound disturbances in a northern Ohio prairie community. For survival, a weak competitive hierarchy developed following gap creation. In contrast, for relative growth, gap creation shifted a distinct competitive hierarchy to conditions of competitive equivalence. The competitive rankings for survival in gaps were opposite those for growth in matrix conditions, with Andropogon being superior in terms of survival and Coreopsis superior in terms of growth. Then, in a factorial design, we teased apart the effects of neighborhood (biomass reduction, size structure, neighbor identity) and abiotic soil changes (mound formation) associated with soil disturbance on these competitive interactions. Abiotic changes associated with mound formation, rather than neighborhood changes, were responsible for the development of the survival hierarchy and the loss of the growth hierarchy following gap creation. When hierarchies formed, matrix species were competitively superior to gap species, supporting the idea of competitive reduction. However, no one matrix species was consistently competitively superior, and under some conditions species were competitive equivalents, partially supporting the idea of competitive change. When disturbance creates conditions of physical stress, as in this case, trade‐offs between growth and survival hierarchies may be important determinants of species response.

show abstract

Gophers and grassland: a model of vegetation response to patchy soil disturbance

Cited by 56 publications

References 15 publications

Long-Term Data Reveal Complex Dynamics in Grassland in Relation to Climate and Disturbance

Long-Term Data Reveal Complex Dynamics in Grassland in Relation to Climate and Disturbance

Multiple Stable Equilibria in Grasslands Mediated by Herbivore Population Dynamics and Foraging Behavior

Do Disturbances Alter Competitive Hierarchies? Mechanisms of Change Following Gap Creation

Contact Info

Product

Resources

About