CURM Eleventh Meeting, 11/11/2008
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- First of all, I hope that you enjoyed the meeting between Drs. Cushing and Hastings. It's always very interesting to hear two scientists coming at the same problem from different directions discuss their issues.
- Action items from our ninth meeting:
- Grayson offered to do some analysis on the males and females (especially cicadas) to see what distinguishes each from the other (mass, wing length, etc.)
- Katie offered to redo her histogram, trying some different bin widths (seeing if she can smooth out the late dip in cicada weights).
- No brilliant resolution to the Lifetouch problem. It does seem that the linear model we found is, indeed, the true linear model -- however bizarre that may seem.
- New Problem of the Week! Something for the bake shop....
- Further discussion of Peter Grant's article as we work towards An article in response to Grant
- Fisher's Equal Investment model: "In the absence of local mate competition the expected sex ratio of sexually dimorphic species is the ratio produced when maternal investment in the two sexes is equal( Fisher, 1930; Trivers & Willard, 1973; Myers, 1978 ). As female wasps are larger than males, males should be produced in greater numbers than females."
- "As female wasps are larger than males, males should be produced in greater numbers than females."
- "Therefore, to produce an excess of male offspring, a female could prey selectively on small prey. At variance with this expectation, however, wasps are believed to hunt selectively for large, and therefore usually female, prey and lay female eggs on them, because female prey outnumber male prey ( Lin, 1979b ). This would tend to yield a female-biased sex ratio."
- Three, non-exclusive, hypotheses of selective predation are tested.
- The first hypothesis is that wasps prey preferentially on one sex of their prey, the more valuable sex ( Trivers & Hare, 1976; Charnov, 1982 ), without specifying a priori whether this is male or female; Lin’s (1979b) argument implicitly assumes it is female.
- The second hypothesis is that wasps choose prey on the basis of the size of their prey (e.g. Kobayashi & Shimada, 2000 ).
- The third hypothesis is that wasps prey preferentially on larger, more conspicuous and hence easier to detect species of cicadas.
- Opportunistic predation, resulting in prey taken at random with respect to their traits, is the default hypothesis to account for data if they are not explained by selective predation.
- Determining whether predation is selective or opportunistic requires estimating prey captured in relation to prey availability. This is difficult to achieve by direct observation because the attacks usually take place at the tops of tall trees.
- As a further extension, weights of individual wasps and of the cicadas they carried were used to test for a positive relationship between the two ( Lin & Michener, 1972 ), as this has so far not been done. [Andy's emphasis]
- We can test this: Strategy: paired t-test
- "...on average [cicada killers'] prey burden is almost twice as heavy as the wasps ( Coelho, 1997 )."
- We can test this: only we have rwl, rather than mass. So we need to model cicada mass based on rwl, and then do a conversion on all pairs.
- A new paper to examine, for next time: Sex Allocation in Solitary Bees and Wasps (Vol. 146, No. 2. The American Naturalist. August 1995, and cited in Peter Grant's article)
- The story I want to work out is between the prey-desirability function, time, and the populations that give rise to the two plots