Milkweed Hypothesis

Discussion: There is a statistically significant positive relationship between the height of the milkweed plant and its number of seedpods. This contradicts the trade-off hypothesis between plant height and the number of seeds produced. The milkweeds may be devoting more resources towards growth earlier in the growing season, and later devoting more resources towards reproduction, which would imply that there is indeed a certain resource allocation strategy that the plants are using, although it is not evident as a negative correlation between the height and number of pods. This trend may also be due to the larger plants simply having more time to produce pods, or have a more extensive root system to acquire nutrients necessary …show more content…
The absence of a negative relationship between these two variables implies that milkweed bugs may not have a major impact on the milkweeds’ reproductive fitness, and therefore it is possible that the population of milkweeds studied may favor a strategy of tolerance of herbivory over defense. This positive correlation observed may be due to a larger number seedpods being able to accommodate a larger number of milkweed bugs in space and as a food source. There was much variability in the number of milkweed bugs present. Potential explanations for this large variability could be due to pods not being counted due to having recently fallen off as the winter approaches, or the milkweed bugs were causing the loss of pods through consumption, while the numbers of bugs stayed the same or increased. The seeds of milkweeds disperse in the fall, which is the time at which these measurements were taken, so it is possible for some samples that there was an unusually high number of milkweed bugs on the plants with a lesser number of seedpods, as the pods had already fallen off after they have dispersed their seeds. According to Ralph (1976), the milkweed bug obtains more nutrition from the inside of the pod, so if the intact shells were counted after the bugs have already dispersed to another plant following consumption of the seeds, it is possible that there was a lower number of milkweed bugs present on some milkweeds with larger numbers of pods. The relationship between the number of large milkweed bugs and the number of pods is further complicated by the fact that some of the pods were not yet open, which would make it harder for the bugs to feed on them. Therefore, a plant with large number of un-split pods could have less bugs than expected. Further studies would need to be conducted in more rigorously controlled conditions to draw strong