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Lower food intake due to domestic grazing reduces colony size and worsens the body condition of reproductive females of harvester ants

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Feeding flexibility is believed to reduce species vulnerability to local extinction associated with environmental changes that cause food shortage, but to what extent such behavioural response is enough to cope with global change is scarcely known in insects. The harvester ant Pogonomyrmex mendozanus modifies its feeding behaviour and widens its diet in response to seed scarcity under grazing and reduces the colony food intake. We tested whether lower food intake, in particular of carbohydrate-rich grass seed, reduces worker survival rate, worsens the body condition of workers and reproductive individuals, and reduces the colony size of P. mendozanus. Our goal was to identify likely links between low quality nutrition and low colony density under heavy grazing previously reported. The reduction of food intake did not affect the body condition of workers, but it was associated with a significant decrease in the colony size and body fat content of queens and gynes. A starvation experiment showed that worker survival did not differ between grazing conditions, but seed deprivation increased worker mortality under all conditions.

Implications for insect conservation

The reduced colony size and deterioration of body condition of reproductive females could impair the survival and reproductive success of P. mendozanus under grazing. These mechanisms may explain the severe decline in colony density in the grazed habitats. In order to protect harvester ants, we highlight the importance of native grass seeds as key resources for population maintenance.

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Data and code available upon request to the corresponding author.


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We thank Javier Lopez de Casenave and several reviewers for critical comments which helped to improve the manuscript. Gualberto Zalazar and Hugo Debandi helped with the field work. We thank to the Telteca park rangers Leonardo Muñoz, Romina Escudero and Ricardo Tamarit for their kind hospitality and logistical assistance. Field and laboratory work was carried out with permission of the Dirección de Recursos Naturales del Gobierno de la Provincia de Mendoza, Argentina (resolutions 473/10, 654/13 and 597/14). Financial support was provided by CONICET (PUE042), Universidad Nacional de Cuyo (SIIP 2019–2021) and by Agencia Nacional de Promoción Científica y Tecnológica of Argentina (PICT 2019-3217). This is contribution number 114 of the Desert Community Ecology Research Team (Ecodes).

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RGP and LM conceptualised the research; RGP and FM conducted the experiments, collected, and analysed the data; RGP wrote the manuscript with LM.

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Correspondence to Rodrigo G. Pol.

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The authors disclose no conflicts of interest of any kind associated with this manuscript.

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Pol, R.G., Miretti, F. & Marone, L. Lower food intake due to domestic grazing reduces colony size and worsens the body condition of reproductive females of harvester ants. J Insect Conserv 26, 583–592 (2022).

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