Density dependence and the spread of invasive big-headed ants (Pheidole megacephala) in an East African savanna

Pietrek, Alejandro G.; Goheen, Jacob R.; Riginos, Corinna; Maiyo, Nelly J; Palmer, Todd M.

doi:10.1007/s00442-021-04859-1

Cited by 7 publications

(13 citation statements)

References 51 publications

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“…Dispersal moves individuals through space (some of these individuals move into uncolonised territory), and population growth causes the low-density edge populations to increase in density over time 129 . The invasion front is characterised by lower densities relative to those behind it 130 . This density gradient moves through space and is persistent over time, so long as the population is spreading 129 .…”

Section: Dominance As a Dispersal Direction Indicator?mentioning

confidence: 99%

The impact of the striped field mouse’s range expansion on communities of native small mammals

Tulis

Ševčík

Radoslava

et al. 2023

Sci Rep

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Understanding species expansion as an element of the dispersal process is crucial to gaining a better comprehension of the functioning of the populations and the communities. Populations of the same species that are native in one area could be considered nonindigenous, naturalised or invasive somewhere else. The striped field mouse has been expanding its range in south-western Slovakia since 2010, although the origin of the spread has still not been clarified. In light of the striped field mouse’s life history, the recent range expansion is considered to be the expansion of a native species. This study analyses the impact of the striped field mouse's expansion on the native population and small mammal communities and confronts the documented stages of striped field mouse expansion with the stages of invasion biology. Our research replicates the design and compares results from past research of small mammals prior to this expansion at the same three study areas with the same 20 study sites and control sites. Several years after expansion, the striped field mouse has a 100% frequency of occurrence in all study sites and has become the dominant species in two of the study areas. The native community is significantly affected by the striped field mouse’s increasing dominance, specifically: (i) we found a re-ordering of the species rank, mainly in areas with higher dominance, and (ii) an initial positive impact on diversity and evenness during low dominance of the striped field mouse turned markedly negative after crossing the 25% dominance threshold. Results suggested that the variation in the striped field mouse’s dominance is affected by the northern direction of its spread. Our findings show that establishment in a new area, spread and impact on the native community are stages possibly shared by both invasive and native species during their range expansion.

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Section: Dominance As a Dispersal Direction Indicator?mentioning

confidence: 99%

The impact of the striped field mouse’s range expansion on communities of native small mammals

Tulis

Ševčík

Radoslava

et al. 2023

Sci Rep

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“…The invasive P. megacephala likely arrived at OPC before 2005 (Riginos et al, 2015). In a concurrent study, we mapped the spatial distribution of P. megacephala invasion to guide our experimental design (Pietrek et al, 2021).…”

Section: Methodsmentioning

confidence: 99%

“…Because P. megacephala kill native Crematogaster ants that defend host trees, and because trees pay a metabolic cost to house Crematogaster ants, we expected P. megacephala invasion (+Inv) to increase λ for trees protected from LMH, but to decrease λ for trees exposed to LMH P. megacephala likely arrived at OPC before 2005 (Riginos et al, 2015). In a concurrent study, we mapped the spatial distribution of P. megacephala invasion to guide our experimental design (Pietrek et al, 2021).…”

Section: Study Systemmentioning

confidence: 99%

“…Commonly known as the big-headed ant, this species is widespread throughout the tropics and subtropics (Wetterer, 2007). By forming supercolonies, these invasive ants are able to dominate expansive areas (Pietrek et al, 2021), suppressing native invertebrates and diminishing biodiversity (Wetterer, 2007). In the Laikipia region of Kenya, P. megacephala initially established in areas of human activity and spread into the surrounding savanna, extirpating native Crematogaster ants, including the two species that most effectively defend host trees (Riginos et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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Demographic consequences of mutualism disruption: Browsing and big‐headed ant invasion drive acacia population declines

Hays

Riginos

Palmer

et al. 2022

Ecology

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Across the globe, biological invasions have disrupted mutualisms, producing reverberating consequences for ecosystems. Although invasive species frequently trigger mutualism disruptions, few studies have quantified the demographic mechanisms by which mutualism breakdown may generate population effects. In a Kenyan savanna, the invasive big-headed ant (Pheidole megacephala) has disrupted a foundational mutualism between the monodominant whistling-thorn tree (Acacia drepanolobium) and native ants (Crematogaster spp.) that deter browsing by large mammalian herbivores. We conducted experiments to quantify the demographic consequences of this mutualism disruption in the presence and absence of large mammalian herbivores. Invasion by P. megacephala exacerbated population declines of A. drepanolobium, primarily through decreased survival and reproduction of adult trees. However, these fitness reductions were small compared to those resulting from the presence of large mammalian herbivores, which negatively impacted growth and survival. Contrary to expectation, the expulsion of metabolically costly Crematogaster mutualists by P. megacephala did not result in higher population growth rates for trees protected from large mammalian herbivores. Our results suggest that invasive P. megacephala may impose a direct metabolic cost to trees exceeding that of native mutualists while providing no protection from browsing by large mammalian herbivores. Across landscapes, we expect that invasion by P. megacephala will reduce A. drepanolobium populations, but that the magnitude and demographic pathways of this effect will hinge on the presence and abundance of browsers.

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“…We conducted the field portion of this study at the neighbouring Ol Pejeta Conservancy ('OPC'; 0°0′52.62″N, 36°51′58.64″E), also in Laikipia County. Pheidole megacephala are expanding on OPC from anthropogenic centres into the surrounding black-cotton savannas at c. 50 m/year (Pietrek et al, 2021). Three invaded and non-invaded site pairs (6 sites total) have been monitored since 2017, and each site contains similar densities of A. drepanolobium mature trees and saplings.…”

Section: Field Experiment: Effect Of P Megacephala On Crown Size In Field Conditionsmentioning

confidence: 99%

A soil‐nesting invasive ant disrupts carbon dynamics in saplings of a foundational ant–plant

et al. 2021

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1. Nearly every terrestrial ecosystem hosts invasive ant species, and many of those ant species construct underground nests near roots and/or tend phloem-feeding hemipterans on plants. We have a limited understanding of how these invasive ant behaviours change photosynthesis, carbohydrate availability and growth of woody plants.2. We measured photosynthesis, water relations, carbohydrate concentrations and growth for screenhouse-reared Acacia drepanolobium saplings on which we had manipulated invasive Pheidole megacephala ants and native Ceroplastes sp. hemipterans to determine whether and how soil nesting and hemipteran tending by ants affect plant carbon dynamics. In a field study, we also compared leaf counts of vertebrate herbivore-excluded and -exposed saplings in invaded and non-invaded savannas to examine how ant invasion and vertebrate herbivory are associated with differences in sapling photosynthetic crown size.3. Though hemipteran infestations are often linked to declines in plant performance, our screenhouse experiment did not find an association between hemipteran presence and differences in plant physiology. However, we did find that soil nesting by P. megacephala around screenhouse plants was associated with >58% lower whole-crown photosynthesis, >31% lower pre-dawn leaf water potential, >29% lower sucrose concentrations in woody tissues and >29% smaller leaf areas. In the field, sapling crowns were 29% smaller in invaded savannas than in non-invaded savannas, mimicking screenhouse results. Synthesis. We demonstrate that soil nesting near roots, a common behaviour byPheidole megacephala and other invasive ants, can directly reduce carbon fixation and storage of Acacia drepanolobium saplings. This mechanism is distinct from the disruption of a native ant mutualism by P. megacephala, which causes similar large declines in carbon fixation for mature A. drepanolobium trees. Acacia drepanolobium already has extremely low natural rates of recruitment from the sapling to mature stage, and we infer that these negative effects of invasion on saplings potentially curtail recruitment and reduce population growth in invaded areas. Our results suggest that direct interactions between invasive ants and plant roots in other ecosystems may strongly influence plant carbon fixation and storage.

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Density dependence and the spread of invasive big-headed ants (Pheidole megacephala) in an East African savanna

Cited by 7 publications

References 51 publications

The impact of the striped field mouse’s range expansion on communities of native small mammals

The impact of the striped field mouse’s range expansion on communities of native small mammals

Demographic consequences of mutualism disruption: Browsing and big‐headed ant invasion drive acacia population declines

A soil‐nesting invasive ant disrupts carbon dynamics in saplings of a foundational ant–plant

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