Crayfish Peer Response (22)


Part 1: Peer Response

In your response, you mention how the numbers of dragonflies and mosquito larvae change due to the presence of crayfish in specific months i.e. March, April, June and July, but it is not affected in May and August. I specifically appreciate how you mention the treatment and the control variables for purposes of clarification. In relation to your question, “Why are dragon-flies not active when they are with crayfish?” the research study by Gary Bucciarelli et al. (126) established the dragonfly nymphs in a majority of cases are terrified by the crayfish. This then allows more mosquito larvae to grow in the water bodies that contain crayfish (Bucciarelli et al. 128). The researchers observed that in streams, or tanks that had dragonfly nymphs, and no crayfish, there was a low number of the mosquito nymphs, and in water bodies that had crayfish, despite having dragonfly nymphs, it seems that the mosquito nymphs were thriving in these water bodies, which contributed to Bucciarelli et al. (127) making the conclusion. This was a vital experiment as it provided evidence on how invasive species can affect the eco-system of an area and contribute to a rise of infection rates for specific diseases (Bucciarelli et al. 128). For instance, in this case, there is a high likelihood of an increase in Malaria cases because of an increase in the number of mosquitoes in the region. However, it is worth noting that the researcher did not specifically and directly answer the question on why dragonflies are not active when they are with crayfish, but makes the inference that they are preys to the crayfish.

Part 2: Results Section

Q. 2

The most important point from the results section is that under natural conditions, it is likely that crayfish reduce the abundance of dragonfly nymphs and their predation efficiency and thereby, directly and indirectly, lead to higher mosquito populations and a loss of ecosystem services related to disease vector control.


There is a significant relationship between crayfish presence and counts of dragonflies and mosquito larvae during March, April, June, and July and the same relationship between crayfish presence and counts of dragonflies and mosquito larvae is not observed in May or August (Bucciarelli et al. 126)

The results showed that the interaction for all predator treatments (crayfish, dragonfly, and combination) significantly affected survival relative to larval survival in the absence of predators (Bucciarelli et al. 127)

The study showed that, on average, when crayfish were present that the dragonflies were in physical contact 64.3% of the time, which means that they were being “distracted” by the crayfish rather than hunting the mosquito larvae and the dragonfly behavioral trends in the combination treatment showed that dragonflies were in physical contact with crayfish (Bucciarelli et al. 128)

When the researcher recoded the model with crayfish as the reference group and compared this treatment with the combination treatment (crayfish: combination), survival over time did not differ significantly between the two indicating that crayfish modified dragonfly nymph behavior in such a way that nymphs essentially became ineffective predators in the presence of crayfish (Bucciarelli et al. 128)

When crayfish and dragonflies appear together (relatively), the survival rate of dragonfly is very low (Bucciarelli et al. 128)

The results indicated that dragonfly nymphs consumed more larvae through time than crayfish alone or when crayfish and dragonfly nymphs foraged together (Bucciarelli et al. 127-8)

Q. 4

Behavioral trends: the way a thing or person reacts or acts is a behavior and when it forms a pattern, then it becomes a behavioral trend.

Significant relationship: in a statistical study, significant relationship refers to the probability that a researcher is right in finding that a relationship exists between variables.

Works Cited

Bucciarelli, Gary M., et al. “Assessing effects of non‐native crayfish on mosquito

survival.” Conservation Biology 33.1 (2019): 122-131.