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211.
  • Östergård, Hannah, 1969- (författare)
  • Plant-seed predator interactions – ecological and evolutionary aspects
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Plant-animal interactions are affected by both abundance and distribution of interacting species and the community context in which they occur. However, the relative importance of these factors is poorly known. I examined the effects of predator host range, environmental factors, host plant populations, plant traits and fruit abortion on the intensity of pre-dispersal seed predation in 46 host populations of the perennial herb Lathyrus vernus. I recorded damage by beetle pre-dispersal seed predators, mainly Apion opeticum and Bruchus atomarius with different host ranges on L. vernus as well as on two additional host plants. Local seed predator population size was mainly influenced by plant population size, current seed production and beetle population size in the previous year, but was not strongly affected by connectivity. The monophagous seed predator was less abundant and had lower densities than the oligophagous. Both predator species had a strong ability to track fluctuations in seed production; intensity of predation increased with relative increases in seed production. Oligophagous predation on L. vernus increased with the abundance of alternative hosts, but presence of L. vernus did not affect predation on alternative hosts. Abundances and trait preferences differed among three co-occurring seed predators, but were also associated with the abundance of the other species. Overall, seed predation influenced selection on flower number. I found clear indications of seed predator offence but no obvious plant defence. The pattern of fruit abortion was associated with reduced plant fitness since the seed predator had an advanced ability to locate fruits with high probability of retention. Taken together, different factors influencing abundance of the seed predator species, different preferences, and context dependent trait selection are likely to result in complex spatio-temporal variation in overall seed losses and trait selection in the common host plant.
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212.
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213.
  • Östergård, Hannah, et al. (författare)
  • Responses of a specialist and a generalist seed predator to variation in their common resource
  • 2009
  • Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 118:10, s. 1471-1476
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluctuations of resources in time and space will influence not only species abundance but also interactions among species. For plant–consumer interactions, the effects of resource variation have mostly been studied in systems with high resource variability. Systems with moderate variations are less studied, although ecological and evolutionary dynamics of plants and consumers are likely to be affected also by less extreme variability. The effects of variation in a particular resource should depend on consumer diet width.We examined how spatial and temporal variation in seed production in the perennial herb Lathyrus vernus influenced population dynamics and resource utilization in two beetle pre-dispersal seed predators with different host ranges over six years. The monophagous Apion opeticum occupied fewer patches and had lower densities than the oligophagous Bruchus atomarius. The proportion of seeds attacked increased with increases in seed production between years for both seed predators. A possible explanation for these patterns is that population dynamics of beetles are driven largely by local factors and that the same factors influence both beetle performance and seed production. In B. atomarius, patterns may also be influenced by a more pronounced preference for L. vernus in years with a high seed production in L. vernus. We conclude that relatively modest variation in seed production may result in responses that differ in both direction and extent from those usually observed in systems with high variation in seed production.
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