Ants And Plants

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types of ants

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o Two types of leaf cutter attine ants- lower and higher. Lower grow fungi on fruits, seeds and insect frass. Higher 5 genera- more abundant and diverse in south America. Of these genera there are the atta-5 spp and acromyrmex- 24spp. These ants excavate nests up to 6m below ground which can contain several million ants and thousands of fungi garden. They are the primary consumers in neotropics terrestrial ecosystems and impact on vegetation is greater than others. They carry out selective herbivory, and affect a mix of tree spp, plant succession and soil process.

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o Cherrett 1986

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amount of vegetation cut from RF by atta alone- 12-17% total leaf production.

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foraging

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forage over 100m from their nests in groups, and there are specialists and generalists. They can concentrate their efforts on one tree for weeks or days.

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leaf cutter-fungi mutualism

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breaks down plant tissue and may detoxify it, making plants available to ants that may have been off limits before. Causes ants to avoid plants that may have fungicidal chemicals, if they forage material toxic to fungus, fungus produces semiochemical which acts as –ive reinforcement. A parasite on fungal gardens, Escovopsis, may stop ants being more proliferate.

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Extra floral nectaries

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secretory tissues in leaves, twigs and on external surfaces. Produce sugar, amino acids and lipids. Beattie 1985- when ants excluded, damage to plants w extra floral nectaries increases, benefit from ants.

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food bodies

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: small epidermal structures, certain proteins lipids etc. collected and taken back to colonies. The specific ant attractant is genetically determined. Investment in FBs depends on ant guard density. Investment is considerable in Macaranga triloba which invests 9% of above ground tissue construction costs in food bodies

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domatia

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stems leaves and spines, myrmecophores. Specific adaptions for ant occupation. Hypertrophy of internal tissue creates internal cavities ants like, who accelerate formation by gnawing. Amazon-380 myrmecophyte individuals per hectare. 16 plant and 25 ant spp.

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Rickson 1979

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2 genera in rubiaceae absorb nutrients from Iridomyrmex colony wastes

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Vasconcelos 1991

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removal of adult herbivores by ants in domatia leads to an increased fruit set

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Fiala 1989

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remove herbivore eggs/ juveniles

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Davidson 1998

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prune encroaching vegetation

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Agrawal 1998

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ant recruitment to leaf damage- 10 minutes in response to release of chemicals by damaged tissues

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3 way systems

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• Messina 1981- plants w ants taller and more seeds
• Horritz and schemshe- 1984- exclusion experiments on Lalathea. Eurybia (caterpillar) and ants. 33% reduction in seed set with ants and 66% reduction without them.
• Bach 1991- removed ants, increased deposition of honeydew- heavy infestations of sooty mould- leaf abscission.

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pollination - rare

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 Galen 1999- formica neorufibarbus dislodges style in flowers of polemonium viscosum. Plants with exclusion of ants- more seed
 Metapleural glands- antimicrobial secretions may harm pollen
 Australian orchids- pollen presented on stalked pollinia, no contact w ant integument. Leporella fumbriata- ant is winged, flower lures ant w female pheromone. Microtis parviflora, pollinators- wingless workers that forage systematically on flwoers.
 Ants not only pollinators in most cases
 Provide large quanities of pollen- gomez and Zamora 1992- large no of ants and liberal pollen yielded reliable seed set.

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ants and seeds

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3000 plant spp have seeds w elaiosome- attractive to ants- adaption to promote removal by ants and dispersal
 Carry the diaspora to their nests, elaisome is removed and eaten, seed discarded in nest/ on waste midden.
 Fatty acid composition similar to insect prey, may be insect mimic.
 n. hemisphere and tropics- benefit from placement of seeds in nutrient enriched microsites, reduction of competition and predation. Improved survivorship in several spp.
 S. hemisphere- different selective pressures- reduction of predation from eed harvesting ant spp, reduction of seedling aggregation and burial at appropriate depth for germination post-fire.
 Clumping of seeds- increased competition, may sometimes eat seeds. Australia- tough seed coats- so protected.

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secondary dispersers

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considerable amount of fruit reaches forest floor- ant abundance- more than 8m per ha. Ants remove intact fruits and seeds from faeces. Removal of fleshy pulp reduces risk of mortality due to fungal infestation. Promotes seed establishement. Leal and olivera- germination success of several spp increased by pulp removal of attine ants, even better than removal by hand due to ant mechanical and chemical factors
 Pizo and olivera 1998- removal of seeds from beneath fruiting trees reduces risk of seed predation by beetles.

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seed harvesting

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dominant in deserts and dry grasslands. More than ½ ant colonies in Australian sites. Can alter local abundance and distribution of ephemeral and annual plants.
 Brown et al 1979- removal of ants from plots in Arizona led to 50% increase in density of annual plants after 2 seasons.
 Briese 1982- ants collected nearly 9000 seeds/m2 during autumn period in semi-arid New South Wales. Ants can remove at least 95% annual seed crop.

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seed selectivity

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- risch and carroll 1986- ants given access to usually dominant spp, reversed competition, exclusion by subordinate. Ants preferred sub and they disappeared. Maintained an equilibrium between sub and dom.

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o Spatial patterns-

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 Clear veg around nests
 Defoliation can be selective
 Alters community composition
 Nowak et al 1990- prevalence of bunchgrass attributed to selective defoliation of other plant spp by P. badius
 Clark and comanor 1975- p. occidentalis clip up to 226m annual plants per ha.

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o Soil

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abandoned nest mounds of p. occidentalis- mat of densely packed roots. 2000-5000x vesicular Arbuscular Mycorrhizal fungal spore density than surrounding vegetation, influence local plant establishment for years. Rising 1981- germination success and seedling recruitment greater in refuse piles of pogonomyrmex ragosus than surrounding area. metapleural secretions protect seedlings from damping off
o Higher soil temp-nest mounds favour some spp.