dimarts, 28 d’abril de 2015

TRUE SEED PREDATORS ....SEED HARVESTING ANTS ..determine the spatio-temporal patterns of the foraging system of the different species; (2) to compare the specific patterns of seed removal and their dependence on seed density and seed size; (3) to evaluate the conse- quences of the different foraging systems of these harvesting ants on the redistribution of seeds of different plant species..IF THEY NOT EAT THE SEEDS SOMETIMES THEY GERMINATE SEED-DISPERSING GROUPS AND SEED-PREDATORS THAT IMPACT IN PLANT POPULATIONS Harvesting ants can affect the regeneration of plants through at least two different processes: seed remo- val and seed dispersal. We analyse the role of differ- ent foraging strategies of ants on patterns of seed removal and dispersal by three Messor species with considerable differences in their foraging systems. Messor capitatus workers rarely leave the nest in well-formed columns, while the other two species form foraging trails, with M. bouvieri forming temporary trails and M. barbarus foraging on a stable system of permanent foraging trails. Overall seed intake of M. capitatus colonies is consider- ably less than that of the two group-foraging species. There are also differences in the size of seeds collected: M. barbarus and M. capitatus harvest similar amounts of large and small seeds, while M. bouvieri harvests small seeds more intensely than large ones, due to the smaller size of the worker caste. The three Messor species differ in the percent of seed dropping of the different seed type and in the seed dispersal distance. Moreover, M. bouvieri and M. capitatus redistributed dropped seeds preferen- tially in bare soil and low sparse vegetation habitats, while M. barbarus redistributed seeds IN HIGH DENSITY HABITATS I S'POSE small-sized shrubs ( Pistacea lentiscus , Rosmarinus officinalis , Dorycnium pentaphyllum , Thymus vulgaris and Coronilla minima ). Three Messor species were found in the study site: M. capitatus , M. bouvieri and M. barbarus. These species have a broad Mediterranean distribution, mainly in open, sunny environments of the Western Mediterranean and North Africa (Bernard, 1968 , 1983 ). Messor bouvieri is mainly limited to coastal areas, while the other two spe- cies are more continental ( M. barbarus can be found up to 800 m and M. capitatus up to 1,100 m). These species differ in their physical caste systems: M. bouvieri has small-sized workers (range of head width: 0.9–2.1 mm), while M. barbarus and M. capitatus are highly poly- morphic species (range of head width: 0.9–3.3 mm in both cases). Their diet is mainly composed of seeds and, to a much lesser extent, other plant and animal remains

  individual-foragers search for and collect seeds independent of one another, and as a result, the whole area surrounding the colony is continuously and simultaneously searched; workers of group-foraging species tend to move together in well-defined columns, so that most of the searching and feeding activities are concentrated in a restricted portion of the area surrounding the nest.Harvester ants do not only collect large numbers of seeds, but they also change the spatial distribution of seeds 

Ants can play an important role in the dynamics of plant communities, acting as seed

dispersal agents in a variety of habitats

Most studies on seed

dispersal by ants have focused on seed dispersal of typical 

myrmecochorous plants whose elaiosome-bearing seedsare especially attractive to ants

 

Asymmetric interactions between plants and seed-harvesting ants in a Mediterranean pasture
interactions between plants and seed-harvesting ants in a Mediterranean pasture is reviewed in this paper. As previously reported in many studies on plant–herbivore interactions, ant–plant relationships are also asymmetric; plants had a larger impact on herbivore dynamics than vice versa. However, the asymmetry did not refer to population dynamics but rather to animal foraging strategies. Ants did not exert a significant influence on vegetation dynamics in terms of plant abundance. The main constraints underlying vegetation change were self-regulation and rainfall. In contrast, the structural characteristics and abundance of vegetation had a significant impact on several important features of food harvesting by ants. This influence was not only associated with their feeding requirements but also with their foraging AND OTHER ASEXUAL activities

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