Overabundance: An Issue for Conservation Biologists?

Garrott, Robert A.; White, P. J.; White, Callie A. Vanderbilt

doi:10.1046/j.1523-1739.1993.740946.x

Cited by 169 publications

(119 citation statements)

References 9 publications

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“…In forest and rangeland ecosystems across the globe, the domination of native plant communities by exotic species and declines in biodiversity are becoming widespread crises (1, 4, 16). Coincidently, recent changes in management of land, livestock, game, and wildlife have resulted in unprecedented increases in managed (e.g., cattle, goats) and wild native (e.g., deer, moose, elk) ungulate populations worldwide (22,47,56). Habitats that experience high ungulate pressure are a recent phenomenon [e.g., overabundant deer and moose in Europe and North America and introduced ungulates in New Zealand and Australia (21-24, 47, 56)] and are likely more susceptible to invasion than those with a long history of browsing (57).…”

Section: Discussionmentioning

confidence: 99%

In a long-term experimental demography study, excluding ungulates reversed invader's explosive population growth rate and restored natives

Kalisz

Spigler

Horvitz

2014

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

128

157

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A major goal in ecology is to understand mechanisms that increase invasion success of exotic species. A recent hypothesis implicates altered species interactions resulting from ungulate herbivore overabundance as a key cause of exotic plant domination. To test this hypothesis, we maintained an experimental demography deer exclusion study for 6 y in a forest where the native ungulate Odocoileus virginianus (white-tailed deer) is overabundant and Alliaria petiolata (garlic mustard) is aggressively invading. Because population growth is multiplicative across time, we introduce metrics that correctly integrate experimental effects across treatment years, the cumulative population growth rate, λ c , and its geometric mean, λ per-year , the time-averaged annual population growth rate. We determined λ c and λ per-year of the invader and of a common native, Trillium erectum. Our results conclusively demonstrate that deer are required for the success of Alliaria; its projected population trajectory shifted from explosive growth in the presence of deer (λ per-year = 1.33) to decline toward extinction where deer are excluded (λ per-year = 0.88). In contrast, Trillium's λ per-year was suppressed in the presence of deer relative to deer exclusion (λ per-year = 1.04 vs. 1.20, respectively). Retrospective sensitivity analyses revealed that the largest negative effect of deer exclusion on Alliaria came from rosette transitions, whereas the largest positive effect on Trillium came from reproductive transitions. Deer exclusion lowered Alliaria density while increasing Trillium density. Our results provide definitive experimental support that interactions with overabundant ungulates enhance demographic success of invaders and depress natives' success, with broad implications for biodiversity and ecosystem function worldwide.life table response experiment | herbivory | biotic resistance | temperate deciduous forest conservation | forest understory herbs S teadily increasing pressure by invasive plant species on native biodiversity (1) disrupts both community and ecosystem function (2) and results in staggering economic costs worldwide (3, 4). A major goal in ecology is to understand how changes over time in species interactions affect invasion success of exotic species (5-8). According to ecological theory, the ability of the resident community to limit the success of invading exotics [biotic resistance (9, 10)] will depend upon ecological context that includes the suite of local interactors (11-15). The abundance of herbivores and their local impacts (11,14,16) can play a prominent role in how fast plant populations grow or shrink and how much the relative abundance of plant species changes over time (5, 15), including changes associated with plant invasions (11,(16)(17)(18)(19). Recently, increased browsing pressure by overabundant ungulate herbivores on native plant communities has been proposed as a fundamental cause of a shift from native to exotic plant domination in forests and rangelands worldwide (11,16,20). Wild and domes...

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Section: Discussionmentioning

confidence: 99%

In a long-term experimental demography study, excluding ungulates reversed invader's explosive population growth rate and restored natives

Kalisz

Spigler

Horvitz

2014

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

128

157

View full text Add to dashboard Cite

show abstract

“…The consequences vary from the addition of new species to drastic disruptions on the community structure (Simberloff and von Holle, 1999;Mack et al, 2000). Nevertheless, there are records of native species becoming increasingly dominant in its original range, a phenomenon known as overabundance (Garrot et al, 1993). Generally, overabundant species are opportunists that respond positively to changes in the original community, a common feature of human-modified landscapes.…”

Section: Introductionmentioning

confidence: 99%

Bamboo overabundance alters forest structure and dynamics in the Atlantic Forest hotspot

Lima

Rother

Muler

et al. 2012

Biological Conservation

135

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“…Although low intensity herbivory may have positive effects on some bird species that prefer open areas (Evans et al 2006;Loe et al 2007), high browsing intensity in a low-productive environment most likely has negative effects on bird diversity and reproduction (Fuller 2001), and in some areas this may be a concern for conservation. As there are currently high densities of wild ungulates in many areas (Garrott et al 1993), indirect effect on other species and trophic levels should be expected. These indirect effects may be hard to predict, as we have seen in this study that two quite similar bird species such as the great tit and the pied flycatcher, react in very different ways to high moose browsing.…”

Section: Discussionmentioning

confidence: 99%

“…The overall moose density in the municipality varies between 1.1-3.4 moose per km 2 (Gundersen et al 2004;Storaas et al 2005), but in winter the effective moose density may be many times higher in the vicinity of feeding stations. High moose densities at feeding stations may be comparable to concentrations of large herbivores around waterholes or salt-licks (Brits et al 2002;Miller and Litvaitis 1992), or areas with extremely high densities due to population increase (Côté et al 2004;Garrott et al 1993;McShea et al 1997).…”

Section: Study Areamentioning

confidence: 99%

“…In Europe, North-America and Japan, the populations of cervids have increased through the last decades, and in some areas to extremely high densities (Côté et al 2004;McShea et al 1997). This increase in cervids has caused some concern for how ecosystem processes and biodiversity may be affected (Fuller and Gill 2001;Garrott et al 1993), and research on how cervids may affect other fauna is needed. The moose (Alces alces) in Fennoscandia is a good example of a cervid that recently has experienced a large population increase (Cederlund and Bergström 1996).…”

Section: Introductionmentioning

confidence: 99%

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