The influence of soil disturbance on seed dispersal by ants in roadside environments - southern NSW, Australia

Zsofia Palfi

Research output: ThesisDoctoral Thesis

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Abstract

Myrmecochory (or seed dispersal by ants) is a common ant-plant mutualistic relationship worldwide. Ants move seeds into their nests to consume the elaiosome, an attractive food reward, and then discard the seed into the surrounding area. Habitat disturbance, such as fire, is known to alter the success of this mutualism by influencing the composition and behaviour of ant communities, however little is known of the effects of soil disturbance. In much of south-eastern Australia, past land-use has resulted in extensive clearing of previous woodlands for agricultural purposes, where remaining patches of remnant vegetation exist mainly in roadside environments. Many roadsides are now of high conservation status, yet regularly disturbed by (soil) disturbances from road management activities.
Field studies were conducted in a typical fragmented agricultural landscape in southern NSW, Australia. The selected area contains a large network of minor rural roads of gravel construction that require periodic management, often associated with soil disturbances. Twenty-four road segments were selected that each contained a non-disturbed (road verge) and a disturbed (by road maintenance) zone. Seeds of Acacia pycnantha, a common myrmecochorous shrub, were offered to ants at multiple seed depots in both zones at each site to conduct observations on ant-seed interactions and subsequent seed dispersal processes.
Ant species richness was greater in the non-disturbed zones, where wide road verges possessed a greater number of species as compared to narrow roadsides. The composition and abundance of individual seed-dispersing ant species varied between disturbed and non-disturbed zones. Overall, 26 ant species were recorded interacting with seeds, however only a few species were responsible for the majority (82%) of ant-seed interactions. In particular, Rhytidoponera metallica and Iridomyrmex purpureus were important contributors in terms of the number of seed removal events. Melophorus bruneus typically performed seed removal events. Smaller bodied Monomorium and Pheidole almost exclusively performed elaiosome consumption, potentially reducing the success of such seeds.
Greater mean seed dispersal distances were recorded in the disturbed zone (mean 12m, maximum 120m), where large meat ants (Iridomyrmex purpureus) were responsible for most of the occasional, long distance dispersals. This species appeared to thrive in the habitat conditions created as a result of soil disturbances from roadworks. Field observations also recorded secondary dispersal events away from nests, which may further aid in seed dispersal. The occasional long distance seed dispersal which were recorded in this study may have direct consequences for plant communities, by facilitating colonization into new sites, and providing habitat connectivity in otherwise fragmented and highly modified rural landscapes.
In summary, despite the severity of disturbances from roadworks, certain ant species prefer to nest in such areas owing to foraging or habitat benefits (e.g. cleared substrate) caused by this form of soil disturbance. Given their contrasting responses to disturbance, there is need for studies to further assess the comparable role of Rhytidoponera and Iridomyrmex as dispersal agents, with particular regard to seed survival and future seedling establishment. The results of this study provide new insights into the mechanisms of seed dispersal by ants occurring in roadside environments and other habitats affected by anthropogenic soil disturbance regimes.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
Supervisors/Advisors
  • Robinson, Wayne, Principal Supervisor
  • Spooner, Peter, Principal Supervisor
Award date01 Jun 2017
Publisher
Publication statusPublished - 01 Jun 2017

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