Control of a Desert-Grassland Transition by a Keystone Rodent Guild

Brown, James H.; Heske, Edward J.

doi:10.1126/science.250.4988.1705

Cited by 565 publications

(539 citation statements)

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“…Further, annuals average only about 6% of total plant cover . Some cases where non-social small mammals have been important in altering plant communities have been in those with a substantial component of annuals (Brown and Heske, 1990), or where outbreaks of small mammals were noted coincident with their impact (Noy-Meir, 1988), neither of which occurred at this site. Although numbers of small mammals can fluctuate widely, those for lagomorphs and the two most abundant species of rodents did not show any unusual peaks from 1994-2001, except for a peak in deer mice in 1996 followed by a crash the next year (Stapp et al, 2008).…”

Section: Discussionmentioning

confidence: 99%

“…Much less is known about the impacts of small specialist herbivores, although again the effects can vary from small to very large (Brown and Heske, 1990;Hulme, 1994;Edwards and Crawley, 1999;Keesing, 2000;Maron and Simms, 2001;Bakker et al, 2006). In some of the cases above, the effects of the small herbivores are due to consumption of seed and seedlings in plant communities with a substantial annual component.…”

Section: Introductionmentioning

confidence: 99%

“…Small mammals with more specialized diets that select for more nutritious seeds and seedlings may be hypothesized to have additive effects on reducing plant diversity (Brown and Heske, 1990;Edwards and Crawley, 1999), which would be greater during wet years in a community such as the shortgrass steppe where seedlings and species dependent on reproduction by seeds are more abundant in wet years. Alternatively, small mammals may have neutral to positive effects on plant diversity in communities where the dominant plants are palatable and are not so productive as to overwhelm the consumptive capacity of the small consumers (Olff and Ritchie, 1998), which would include shortgrass steppe .…”

Section: Introductionmentioning

confidence: 99%

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Plant community dynamics in shortgrass steppe with grazing relaxation and imposition by large and small herbivores

Milchunas

2011

Israel J Ecol Evol

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Semiarid rangelands often respond slowly to rest/relaxation of grazing pressure by large herbivores, and the effects of grazing are most often inferred from this direction of study because the imposition of grazing onto previous ungrazed/lightly grazed areas occurred prior to the age of scientific studies. These rangelands host a diversity of small and large herbivores, but grazing studies most often concern effects of the large generalists. Here, the effects of herbivore body size on plant species richness and dominant species, and imposition and relaxation of grazing by large herbivores were studied by opening half of exclosures established in 1939 and building new exclosures to large herbivores, and to small-plus-large herbivores. Plant richness using sensitive species-area sampling was studied in a dry and a wet year, about 62 years after initiating the long-term experiment and about 6-10 years after initiating the altered designs. Convergence of the newly opened to large herbivore grazing treatment to the long-term grazed treatment occurred within 10 years, but convergence of the newly excluded to large herbivore treatment to the long-term excluded treatment had only partly occurred. This indicated that recovery from grazing is slow relative to imposition of grazing by large herbivores, but effects of the additional exclusion of small-plus-large herbivores occurred relatively rapidly. These results were mirrored by trajectories of convergence of the dominant species, and this is discussed with respect to implications for state-and-transition models. Short-term exclusion of small-plus-large herbivores resulted in greater richness than even long-term exclusion of only large herbivores, even though quantities consumed by small herbivores are much less than by large. Grazing effects on plant richness were large in the wet year, but the very dry year suppressed richness on all treatments. When sampling effort and area are the same, the numbers and attributes of species unique to a treatment are indicators of rareness of the richness and traits selected for by the treatment. More unique species were sampled in the small-plus-large herbivore exclosures when comparing body size, and the long-term large herbivore exclosures when comparing time of exclosure. Unique species encountered during sampling the ungrazed treatments were generally forbs, exotic and/or weedy invasive species, and often tall, annual species.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Plant community dynamics in shortgrass steppe with grazing relaxation and imposition by large and small herbivores

Milchunas

2011

Israel J Ecol Evol

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“…In other words, the per capita probability of seedling mortality is nonrandom because the probability of death is not the same for all individuals in a local community -it is dependent to some degree on species identity. In plant communities in which generation times are relatively short, experiments have demonstrated that nonrandom mortality through these early transitions can be sufficiently strong to affect the species composition of mature plants (26)(27)(28)(29). Such demonstrations are impossible in studies of a few decades or less in duration when generation times are long and even juveniles live for several decades or centuries, such as in many tropical forests.…”

mentioning

confidence: 98%

Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

Green

Harms

Connell

2014

Proc. Natl. Acad. Sci. U.S.A.

109

116

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A variety of ecological processes influence diversity and species composition in natural communities. Most of these processes, whether abiotic or biotic, differentially filter individuals from birth to death, thereby altering species' relative abundances. Nonrandom outcomes could accrue throughout ontogeny, or the processes that generate them could be particularly influential at certain stages. One long-standing paradigm in tropical forest ecology holds that patterns of relative abundance among mature trees are largely set by processes operating at the earliest life cycle stages. Several studies confirm filtering processes at some stages, but the longevity of large trees makes a rigorous comparison across size classes impossible without long-term demographic data. Here, we use one of the world's longest-running, plot-based forest dynamics projects to compare nonrandom outcomes across stage classes. We considered a cohort of 7,977 individuals in 186 species that were alive in 1971 and monitored in 13 mortality censuses over 42 y to 2013. Nonrandom mortality with respect to species identity occurred more often in the smaller rather than the larger size classes. Furthermore, observed nonrandom mortality in the smaller size classes had a diversifying influence; species richness of the survivors was up to 30% greater than expected in the two smallest size classes, but not greater than expected in the larger size classes. These results highlight the importance of early life cycle stages in tropical forest community dynamics. More generally, they add to an accumulating body of evidence for the importance of early-stage nonrandom outcomes to community structure in marine and terrestrial environments. diversity | early life-cycle stages | nonrandom | tropical forest P rocesses that operate nonrandomly with respect to species identity contribute to the structure of natural communities (1-3). Evidence from diverse rain forests includes demographic transitions from seeds to seedlings (4, 5), at the seedling (6, 7) and sapling stages (8) and among large trees (9-12). Although the relative contributions of nonrandom processes at each life cycle stage to determining patterns of abundance and diversity in the mature canopy are unknown, one long-standing paradigm is that community assembly is mediated primarily by events occurring from seed dispersal through seedling germination and small-sapling establishment (13-17). However, despite suggestive patterns (6,7,18,19), evidence is lacking for the comparative strength of early-stage dynamics in determining canopy abundance and diversity.Numerous studies demonstrate significant interspecific variation in the susceptibility of tropical tree seedlings to postgermination hazards, including natural enemies (20, 21), adverse climatic or edaphic conditions (22), physical damage (23), and the crowding or shared-enemies effects of con-and heterospecific neighbors (24,25). In other words, the per capita probability of seedling mortality is nonrandom because the probability of death is not t...

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“…Benthlc ecologists must expand their efforts to encompass longer and larger scales (Brown 1995). Some work of this nature has been done (e.g.…”

Section: Effects Of Human Exploitationmentioning

confidence: 99%

Marine ecological research in seashore and seafloor systems:accomplishments and future directions

Estes¹,

Peterson²

2000

Mar. Ecol. Prog. Ser.

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Research in seashore and seafloor communlt~es has contributed mmensely to the conceptual growth of ecology Here we summarize some of the most Important findings and discuss needs and opportunities for future work Dispropoi t~onately large numbers of the most influential contrlbutlons are derived from studies of rocky short 5 and coral reefs because aspects of these systems (accessibility) and of their most common species (sessile or weaklv motile, high density short generation tline) make them well suited to manipulative experiments Foremost among the research contributions froin seashore and seafloor systems are increased understanding of (1) competition and consumer-prey interactions, (2) trophic cascades and other Indirect specles ~nteractions (3) the evolution of defense and resistance in consumer-prey systems (4) the importance of propagule transport and recruitment v a n a t~o n to adult populations (5) the impacts of physlcal d~sturbance and (6) the generation and maintenance of specles diversity on ecological t~r n e scales We acknowledge the importance of manipulative expenments in the growth of marine ecology but question whether a stnct adherence to this approach will best serve future needs Some of the most pressing needs for future knowledge are (1) documenting the complex influences of spatial and temporal scales on ecological processes, (2) identifying the role of large, mobile predators in manne ecosystems, (3) understanding factors hmitlng manne autotrophs, (4) integrating historical biology and neontology and (5) appreciating intersystem linkages Increased attention to conducting arrays of expenments, taking measurements and observations, and documenting change at larger scales of space and time will provlde lnsights that are unattainable by the commonly used methodological protocols Novel approaches, including (1) evaluating and managing human disturbance for the loint purpose of conservation and learning, (2) developing stronger ties between scientists worhlng in open-ocean and near-shore systems and (3) developing collaborative prolects among scientists In the academic governmental, and pnvate sectors are required to understand many of these processes

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Control of a Desert-Grassland Transition by a Keystone Rodent Guild

Cited by 565 publications

References 18 publications

Plant community dynamics in shortgrass steppe with grazing relaxation and imposition by large and small herbivores

Plant community dynamics in shortgrass steppe with grazing relaxation and imposition by large and small herbivores

Nonrandom, diversifying processes are disproportionately strong in the smallest size classes of a tropical forest

Marine ecological research in seashore and seafloor systems:accomplishments and future directions

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