Ecological engineering by a native leaf-cutting ant increases the performance of exotic plant species

Applied Vegetation Science

et al. 2012

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Question Low quantities of soil nutrients often restrict plant establishment and growth in arid lands and have been partially attributed to the scarcity of organic matter in these ecosystems. Refuse dumps from leaf‐cutting ants are a natural source of organic matter; however, their effects on native plant performance have received limited attention to date. Do refuse dumps from leaf‐cutting ants (Acromyrmex lobicornis) enhance the germination and growth of several native plant species and what is the potential influence of heavy grazing on this practice? Location Monte Desert, Neuquén Province, Argentina. Methods We collected fruits of five plant species and two types of substrate (ant refuse dump vs control soil) from two known paddocks with different livestock densities (high vs low). We sowed seeds, previously weighed, of each species in both substrates from both paddocks and monitored their development. We harvested emerged seedlings, documenting their age and measured their height, weight, number of leaves, root weight and root length. Results Seed weight was lower in the highly grazed paddock for all the plant species studied. However, seed weight did not affect germination rate. Refuse dumps from the less grazed paddock (i.e. with higher nutrient content) enhanced the vigour of seedlings from smaller seeds more often than those from the highly grazed paddock. Also, germination improved when both seeds and substrate were from the less grazed paddock. Vigour variables showed more complex results, but seedlings growing in refuse dumps tended to be more vigorous. Refuse dumps from the less grazed paddock (i.e. with higher nutrient content) enhanced the vigour of seedlings from the highly grazed paddock (smaller) more than the seeds from the less grazed paddock (larger). Conclusions Our results demonstrated that ant refuse dumps increased plant germination rate and improved performance of the most representative vegetation in the Monte Desert. Given that external refuse dumps from leaf‐cutting ants are a renewable resource, very abundant and easy to collect, this substrate could be used as a free natural fertilizer in arid regions to restore and manage vegetation cover, especially in heavily grazed sites.

Section: Introductionmentioning

confidence: 99%

Effects of leaf‐cutting ant refuse on native plant performance under two levels of grazing intensity in the Monte Desert of Argentina

Cerda

Tadey

Applied Vegetation Science

et al. 2012

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“…For example, Lactuca serriola contains latex, which has been reported to be toxic to most herbivores (Ramos et al 2010). Carduus thoermeri and Onopordon accanthium have relatively high levels of foliar nutrients (Farji-Brener and Ghermandi 2008;Farji-Brener et al 2010), and this could explain their high damage levels reported in this study. Thus, plants in this study have a great variety of defenses, even when six of them belong to the same family.…”

Section: Discussionmentioning

confidence: 58%

Foliar herbivory and its effects on plant growth in native and exotic species in the Patagonian steppe

Pirk

2012

Ecological Research

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Studies of herbivory and its consequences on the growth of native and exotic plants could help elucidate some processes involved in plant invasions. Introduced species are likely to experience reduced herbivory in their new range due to the absence of specialist enemies and, thus, may have higher benefits if they reduce the investment in resistance and increase their compensatory capacity. In order to evaluate the role of herbivory in disturbed areas within the Patagonian steppe, we quantified and compared the leaf levels of herbivory of four native and five exotic species and recorded the associated insect fauna. We also performed greenhouse experiments in which we simulated herbivory in order to evaluate the compensatory capacity of native and exotic species under different herbivory levels that resembled naturally occurring damage. Natural herbivory levels in the field were similar between the studied exotic and native plants. Field observations confirmed that they both shared some herbivore insects, most of which are generalists. In the greenhouse experiments, both exotic and native plants fully compensated for herbivory. Our results suggest that the studied exotic plants are not released from herbivory in the Patagonian steppe but are able to fully compensate for it. The capacity to recover from herbivory coupled with other potential adaptations, such as a better performance under disturbance and greater competitive ability than that of the native species, may represent some of the mechanisms responsible for the success of plant invasion in the Patagonian steppe.

“…Specifically, root growth is particularly enhanced in plants growing on refuse materials, leaf‐cutting ant nests and dry habitats. As we showed that refuse materials have higher nutrient content than nest soils, it is reasonable that the roots that access this substrate show greater growth (Farji‐Brener & Ghermandi ; Farji‐Brener, Lescano & Ghermandi ). The huge production of refuse material, high ant density and colossal dimensions of leaf‐cutting ant nests may enhance this process (Farji‐Brener & Werenkraut ).…”

Section: Discussionmentioning

confidence: 81%

“…This positive effect of ant nests on individual plants apparently does not extend to population and community levels. It is known that not all plant species respond equally to the excess of soil resources (Farji‐Brener, Lescano & Ghermandi ). Moreover, the physical characteristics of ant nests and the changes in microclimatic conditions generated by ant activities may act as ecological filters for plant recruitment disfavouring or favouring particular species (Garrettson et al .…”

Section: Discussionmentioning

confidence: 99%

“…Accordingly, there is contrasting evidence on whether plants growing around ant nests increase their performance and/or abundance (Horvitz & Schemske ; Whitford & Di Marco ; Wagner ; Frouz et al . ; Farji‐Brener, Lescano & Ghermandi ; Saha et al . ), and the effects of ant nests on plant diversity (Beattie & Culver , ; King ; Lewis, Franceschi & Stofella ; Farji‐Brener & Ghermandi ).…”

Section: Introductionmentioning

confidence: 99%

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The effects of ant nests on soil fertility and plant performance: a meta‐analysis

Journal of Animal Ecology

Werenkraut

2017

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107

Ants are recognized as one of the major sources of soil disturbance world-wide. However, this view is largely based on isolated studies and qualitative reviews. Here, for the first time, we quantitatively determined whether ant nests affect soil fertility and plant performance, and identified the possible sources of variation of these effects. Using Bayesian mixed-models meta-analysis, we tested the hypotheses that ant effects on soil fertility and plant performance depend on the substrate sampled, ant feeding type, latitude, habitat and the plant response variable measured. Ant nests showed higher nutrient and cation content than adjacent non-nest soil samples, but similar pH. Nutrient content was higher in ant refuse materials than in nest soils. The fertilizer effect of ant nests was also higher in dry habitats than in grasslands or savannas. Cation content was higher in nests of plant-feeding ants than in nests of omnivorous species, and lower in nests from agro-ecosystems than in nests from any other habitat. Plants showed higher green/root biomass and fitness on ant nests soils than in adjacent, non-nest sites; but plant density and diversity were unaffected by the presence of ant nests. Root growth was particularly higher in refuse materials than in ant nest soils, in leaf-cutting ant nests and in deserts habitats. Our results confirm the major role of ant nests in influencing soil fertility and vegetation patterns and provide information about the factors that mediate these effects. First, ant nests improve soil fertility mainly through the accumulation of refuse materials. Thus, different refuse dump locations (external or in underground nest chambers) could benefit different vegetation life-forms. Second, ant nests could increase plant diversity at larger spatial scales only if the identity of favoured plants changes along environmental gradients (i.e. enhancing β-diversity). Third, ant species that feed on plants play a relevant role fertilizing soils, which may balance their known influence as primary consumers. Fourth, the effects of ant nests as fertility islands are larger in arid lands, possibly because fertility is intrinsically lower in these habitats. Overall, this study provide novel and quantitative evidence confirming that ant nests are key soil modifiers, emphasizing their role as ecological engineers.