Do seed harvesting ants threaten the viability of a critically endangered non‐myrmecochorous perennial plant population? A complex interaction

Abstract

This study analyzes the fate of seeds removed by ants, as well as the seed supply, seedling survival, and the ability to form persistent seed banks in the soil, in a critically endangered population of the non-myrmecochorous perennial halophyte Helianthemum polygonoides, in order to determine the extent to which seed removal by ants represents a real bottleneck for recruitment and thus a threat for long-term population viability. Apparently, the impact of seed-harvester ants was dramatic: the primary seed shadow was reduced by up to 93% by the activity of Messor bouvieri and Aphaenogaster dulcineae. However, M. bouvieri lost 7% of fruits collected by dropping them on trunk trails, mostly under plant cover, the most propitious microenvironment for recruitment. In addition, some seeds were mistakenly rejected in refuse piles, although here recruitment was extremely low. A significant fraction of seeds (&40%) remained viable in the soil for over 2 years. In addition, H. polygonoides had the ability to form shortterm persistent seed banks, in spite of the intense ant seed removal. In general, seedling recruitment was very low, denoting the scarcity of safe sites in the habitat. Overall, the data corroborate that seed removal by ants, although highly intense, does not compromise the viability of perennial-plant populations, because seed supply and seed reserve in the soil are enough to exploit current and future safe sites. A population viability analysis demonstrated that other threats affecting the survival of reproductive H. polygonoides plants actually constitute the real risk for the conservation of this critically endangered species.

New threats for a protected plant: the need to review and update recovery plans of endangered species

“…Furthermore, matrix models of population viability have demonstrated that the demographic bottleneck of H. polygonoides is in the abundance of mature individuals (i.e., age range which will be only negatively affected if the habitat is destroyed) (Copete et al 2009;Martínez-Duro et al 2010). Those ecological features support our ndings and contribute to understand the chorological and demographic trends of H. polygonoides.…”

Germination and soil seed bank traits of Podocarpus angustifolius (Podocarpaceae): an endemic tree species from Cuban rain forests

“…A persistent seed bank can be crucial in ensuring the conservation of a species, since it allows the re-establishment and maintenance of plant populations after disturbances, although no external source of propagules occurs (Baskin & Baskin 1978). In fact, Thompson et al (1997) suggested that short-term persistent soil seed banks play an essential role in the viability of populations, as Martínez-Duro et al (2010) empirically demonstrated for a critically endangered perennial plant species.…”

Plant Production Protocols from Seeds of Threatened Atropa baetica and Widespread A. belladonna, Both Rich in Alkaloids

“…The numbers of viable recovered seeds were reduced, with 262 and 294 seeds/m 2 for A. belladonna and A. baetica, respectively, but these values are very important in a population dynamics context because these species are unusual and the formation of persistent soil seeds banks can allow the recruitment of seedlings for years, especially when fruit formation might be affected by events such as herbivory or destruction by summer storms [18]. Similarly, population viability analyses have also stressed the important roles of soil seed banks in the long-term persistence of populations of perennials, such as Helianthemum polygonoides, which is a critically endangered perennial shrub in southeast Spain [38]. Vegetative propagation appears to be more important for seedling recruitment than seed germination for the study species, but seeds play a crucial role in the renewal of adult individuals, which can live more than 20 years (personal observation), although they inevitably die.…”