Hawkins et al 1997

The authors used life tables of insects to quantify levels of enemy induced mortality. Three factors were analyzed for differences in assocation: enemy type, (predator, parasitoid, or pathogen), the developmental stage of the insect (egg, early larva, mid-larva, late larva, and pupa) when killed, and ecological characteristics of the herbivores (feeding biology, invasion status, and the cultivation status and latitudinal zone of the habitat).

Major Findings:

-Mortality by predators is greater in the later developmental stages.

-Parasitoids kill more than predators or pathogens.

-Fewer endophytes are killed by pathogens and predators than exophytes.

-Within endophytes: leaf miners had the greatest mortality by parasitoids. Galler/borers/root feeders have the lowest mortality by parasitoids.

-Mortality caused by enemies is similar in natural and cultiviated habitats.

-Exotic and native insects do not suffer different enemy induced mortality rates.

- Tropical/subtropical habitats suffer more predation and pathogens.

-Temperate habitats suffer more from parasitism.

In a previous, similar study, the authors had classified mortality into 6 sources. Each of these sources was grouped by ecological category and developmental stage in the life table. They found that source of mortality 1. changed as the herbivores developed and 2. was strongly influenced by feeding biology. They also found that enemy attach was the most frequent cause of death for the herbivores, but were unable to distinguish the different types of enemies. For the present study, one of their goals was to the examine enemy induced mortality in greater detail.

Some issues discussed in class:
-Medians were used as a measure central tendency because the data were not distributed normally.
-The authors cited themselves often, probably to justify why they published two papers.
-For Bonferroni analysis, the accepted p values was very small. The reason for this is because it was a meta-analysis and many studies can accumulate a lot of error.