Abstract
The dispersal capacity of plant species that rely on animals to disperse their seeds (biotic dispersal) can alter with changes to the populations of their keystone dispersal vectors. Knowledge on how biotic dispersal systems vary across landscapes allows better understanding of factors driving plant persistence. Myrmecochory, seed dispersal by ants, is a common method of biotic dispersal for many plant species throughout the world. We tested if the seed dispersal system of Acacia terminalis (Fabaceae), a known myrmecochore, differed between two elevations in the Greater Blue Mountains World Heritage Area, in southeastern Australia. We compared ant assemblages, seed removal rates of ants and other vertebrates (bird and mammal) and the dominant seed-dispersing ant genera. At low elevations (c. 200 m a.s.l) seed removal was predominantly by ants, however, at high elevation sites (c. 700 m a.s.l) vertebrate seed dispersers or seed predators were present, removing over 60% of seeds from experimental depots when ants were excluded. We found a switch in the keystone seed-dispersing ant genera from Rhytidoponera at low elevations sites to Aphaenogaster at high elevation sites. This resulted in more seeds being removed faster at low elevation sites compared to high elevation sites, however long-term seed removal rates were equal between elevations. Differences in the keystone seed removalist, and the addition of an alternate dispersal vector or seed predator at high elevations, will result in different dispersal and establishment patterns for A. terminalis at different elevations. These differences in dispersal concur with other global studies that report myrmecochorous dispersal systems alter with elevation.
Highlights
Understanding how seed dispersal systems change across landscapes is crucial to understanding plant species’ population dynamics and current and future plant distributions [1]
We aimed to determine if seed dispersal systems differed between two elevations (c. 200 m and c. 700 m), within a myrmecochory ‘hotspot’; the Greater Blue Mountains World Heritage Area, New South Wales, Australia, where c. 200 plant species (13%) have seeds adapted for dispersal by ants [27]
As temperatures increased at high elevation sites more seeds were found by ants and more seeds were removed by ants; this relationship reversed at low elevation sites
Summary
Understanding how seed dispersal systems change across landscapes is crucial to understanding plant species’ population dynamics and current and future plant distributions [1]. The dispersal abilities of plant species whose seeds are dispersed by animals (biotic dispersal) can change significantly with variation in the dispersal vector [2]. Over 11 532 plant species are myrmecochorous, i.e. their seeds are dispersed by ants Australia is recognised as a myrmecochory ‘hot spot’ with over 1500 myrmecochorous plant species [7]. Ant communities and ant seed dispersal systems are known to change with elevation [15,16,17]. Seed removal rates can increase [18] or decrease with elevation [19], as can the abundance of myrmecochorous ant species [15, 19]. In Australia, studies on seed removal by ants have been primarily conducted at low elevations, i.e. We aimed to determine if seed dispersal systems differed between two elevations (c. 200 m and c. 700 m), within a myrmecochory ‘hotspot’; the Greater Blue Mountains World Heritage Area, New South Wales, Australia, where c. 200 plant species (13%) have seeds adapted for dispersal by ants [27]
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