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mutualism (2).docx

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McMaster University
Kim Dej

November 1 , 2012 Biology 2F03: Fundamental and Applied Ecology Mutualism (2) Ants - fast and agile runners, - good vision - forage independently - benefit: large colony size - Newly mated queens find unoccupied seedlings or shoots of bullshorn acacia - usually colony starts with one fertilized queen - a young queen excavates entrance in one green thorn lays first eggs in thorn begins to forage - gets nectar for herself and developing larvae from the foliar nectaries and the beltian bodies - colony grows (workers) actively take up chores of colony  abdomen enlarges and she becomes sedentary Question - ants clearly benefit from the arrangement but what is the benefit to the plant Benefits for plants - ants are the abundance of herbivorous insects on bullshorn acacia - ants are predators - acacia shoots without ants have much larger numbers of herbivorous insects - ants have similar arrangements with our native trees (e.g. aspen where they tend aphids; which obtain sugar from the plants) - survival of acacia shoots with and without resident ants - survival, growth rate and visible abundants of insects Growth of acacia with and without resident ants - growth rate increases with ants - acacia shoots with ants grew much faster Acacia-ant mutualism overview - in exchange for food and shelter, ants protect acacias from attack by herbivores and competition from other plants - why are there no other plants growing beside acacia: ants go after anything that might affected acacia - acacias release chemicals warning other acacias in the area - workers will attack, bite and sting all insects or large herbivores (cattle, antelopes) - workers kill any vegetation encroaching on the host tree - workers keep acacia free from competition for water, light, nutrients by other trees, shrubs and vines - the host plant and ants benefit in many ways Question - how flexible are mutualistic relationships - are they inherently beneficial Temperate system: alpine Aspen sunflowers - aspen sunflowers attract ants by producing nectar at extrafloral nectaries structures outside of the flowers - extrafloral nectar rich in sucrose and high concentrations of amino acids - similar to swollen thorn acacias; but does not provide living spaces - clear benefit for ants…what about sunflowers? - Camas quamash is another example of similar relationship Other actors do matter - ants will attack other herbivores - grey sunflower seed weevil and banded sunflower moths are bad for the sunflowers because they attack the seeds of sunflowers - in the central Rocky Mountains, a variety of speed predators attack sunflowers - seed predators damaged over 90% of the seeds produced - high densities of ants (50 per plant) deter seed predators Facultative vs obligate - Relationship between ants and aspen sunflowers is facultative - the relationship between ants and acacia is obligate. Why not obligate on aspen sunflowers - long-term study: every few years the flower heads of aspen sunflowers are
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