Effects of native diversity, soil nutrients, and natural enemies on exotic invasion in experimental plant communities

Heckman, Robert W.; Halliday, Fletcher W.; Wilfahrt, Peter A.; Mitchell, Charles E.

doi:10.1002/ecy.1796

Cited by 44 publications

(80 citation statements)

References 71 publications

(218 reference statements)

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“…In this system, exotic hosts were largely introduced by humans from fertilised pastures (Fridley ), benefit from experimental fertilisation more than their native counterparts (Heckman et al . , ), are sensitive to initial host diversity, and on average, experience heavier parasite loads than their native counterparts (Heckman et al . ).…”

Section: Discussionmentioning

confidence: 99%

“…Because this study aimed to examine how plant community structure and disease change over time, we did not weed plots to maintain richness (Fargione & Tilman ; Heckman et al . ). Thus, the host diversity treatments represent initial conditions and not the diversity of a plot after July 2012.…”

Section: Methodsmentioning

confidence: 97%

“…In 2013, host community structure was characterised by a few common species and many rare species (Heckman et al . ). Because common species contribute more to parasite abundance (Mordecai ; Heckman et al .…”

Section: Methodsmentioning

confidence: 97%

“…; Heckman et al . ). Exotic species often initially escape the parasites that infected them in their native range (Mitchell & Power ; Mitchell et al .…”

Section: Introductionmentioning

confidence: 97%

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Past is prologue: host community assembly and the risk of infectious disease over time

et al. 2018

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Infectious disease risk is often influenced by host diversity, but the causes are unresolved. Changes in diversity are associated with changes in community structure, particularly during community assembly; therefore, by incorporating change over time, host community assembly may provide a framework to resolve causation. In turn, community assembly can be driven by many processes, including resource enrichment. To test the hypothesis that community assembly causally links host diversity to future disease, we experimentally manipulated host diversity and resource supply to hosts, then allowed communities to assemble for 2 years (surveyed 2012–2014). Initially, host diversity increased disease. Subsequently, host diversity did not directly alter disease. However, host diversity determined the trajectory of host community assembly, altering colonisation by exotic host species and richness‐independent host phylogenetic diversity, which together reversed the initial increase in disease. Ultimately, incorporating the temporal dimension of community assembly revealed novel mechanisms linking host diversity to future disease.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 97%

Section: Methodsmentioning

confidence: 97%

“…; Heckman et al . ). Exotic species often initially escape the parasites that infected them in their native range (Mitchell & Power ; Mitchell et al .…”

Section: Introductionmentioning

confidence: 97%

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Past is prologue: host community assembly and the risk of infectious disease over time

et al. 2018

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“…, Sandel and Corbin ), and that resource availability or natural enemies can drive invasibility with no effects of diversity (Heckman et al. ). Hence, the role that diversity plays in influencing invasibility appears to be dependent on other factors, factors that can covary with diversity and even override diversity's effects on invasibility.…”

Section: Introductionmentioning

confidence: 99%

The fluctuating resource hypothesis explains invasibility, but not exotic advantage following disturbance

Pearson

Ortega

Villarreal³

et al. 2018

Ecology

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Invasibility is a key indicator of community susceptibility to changes in structure and function. The fluctuating resource hypothesis (FRH) postulates that invasibility is an emergent community property, a manifestation of multiple processes that cannot be reliably predicted by individual community attributes like diversity or productivity. Yet, research has emphasized the role of these individual attributes, with the expectation that diversity should deter invasibility and productivity enhance it. In an effort to explore how these and other factors may influence invasibility, we evaluated the relationship between invasibility and species richness, productivity, resource availability, and resilience in experiments crossing disturbance with exotic seed addition in 1-m plots replicated over large expanses of grasslands in Montana, USA and La Pampa, Argentina. Disturbance increased invasibility as predicted by FRH, but grasslands were more invasible in Montana than La Pampa whether disturbed or not, despite Montana's higher species richness and lower productivity. Moreover, invasibility correlated positively with nitrogen availability and negatively with native plant cover. These patterns suggested that resource availability and the ability of the community to recover from disturbance (resilience) better predicted invasibility than either species richness or productivity, consistent with predictions from FRH. However, in ambient, unseeded plots in Montana, disturbance reduced native cover by >50% while increasing exotic cover >200%. This provenance bias could not be explained by FRH, which predicts that colonization processes act on species' traits independent of origins. The high invasibility of Montana grasslands following disturbance was associated with a strong shift from perennial to annual species, as predicted by succession theory. However, this shift was driven primarily by exotic annuals, which were more strongly represented than perennials in local exotic vs. native species pools. We attribute this provenance bias to extrinsic biogeographic factors such as disparate evolutionary histories and/or introduction filters selecting for traits that favor exotics following disturbance. Our results suggest that (1) invasibility is an emergent property best explained by a community's efficiency in utilizing resources, as predicted by FRH but (2) understanding provenance biases in biological invasions requires moving beyond FRH to incorporate extrinsic biogeographic factors that may favor exotics in community assembly.

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Systematic reduction of natural enemies and competition across variable precipitation approximates buffelgrass invasiveness (Cenchrus ciliaris) in its native range

Rhodes,

Plowes,

Bowman

et al. 2024

Ecology and Evolution

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Invasive grasses cause devastating losses to biodiversity and ecosystem function directly and indirectly by altering ecosystem processes. Escape from natural enemies, plant–plant competition, and variable resource availability provide frameworks for understanding invasion. However, we lack a clear understanding of how natural stressors interact in their native range to regulate invasiveness. In this study, we reduced diverse guilds of natural enemies and plant competitors of the highly invasive buffelgrass across a precipitation gradient throughout major climatic shifts in Laikipia, Kenya. To do this, we used a long‐term ungulate exclosure experiment design across a precipitation gradient with nested treatments that (1) reduced plant competition through clipping, (2) reduced insects through systemic insecticide, and (3) reduced fungal associates through fungicide application. Additionally, we measured the interaction of ungulates on two stem‐boring insect species feeding on buffelgrass. Finally, we measured a multiyear smut fungus outbreak. Our findings suggest that buffelgrass exhibits invasive qualities when released from a diverse group of natural stressors in its native range. We show natural enemies interact with precipitation to alter buffelgrass productivity patterns. In addition, interspecific plant competition decreased the basal area of buffelgrass, suggesting that biotic resistance mediates buffelgrass dominance in the home range. Surprisingly, systemic insecticides and fungicides did not impact buffelgrass production or reproduction, perhaps because other guilds filled the niche space in these highly diverse systems. For example, in the absence of ungulates, we showed an increase in host‐specific stem‐galling insects, where these insects compensated for reduced ungulate use. Finally, we documented a smut outbreak in 2020 and 2021, corresponding to highly variable precipitation patterns caused by a shifting Indian Ocean Dipole. In conclusion, we observed how reducing natural enemies and competitors and certain interactions increased properties related to buffelgrass invasiveness.

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Effects of native diversity, soil nutrients, and natural enemies on exotic invasion in experimental plant communities

Cited by 44 publications

References 71 publications

Past is prologue: host community assembly and the risk of infectious disease over time

Past is prologue: host community assembly and the risk of infectious disease over time

The fluctuating resource hypothesis explains invasibility, but not exotic advantage following disturbance

Systematic reduction of natural enemies and competition across variable precipitation approximates buffelgrass invasiveness (Cenchrus ciliaris) in its native range

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