Longhorned beetle (Coleoptera: Cerambycidae) diversity in a fragmented temperate forest landscape

Longhorned beetles (Coleoptera: Cerambycidae) are an important component of temperate forest ecosystems. We trapped longhorned beetles in forests in northwest Ohio during 2008 to test the hypothesis that larger forests have greater species diversity than smaller forests. Large forests had a significantly greater cerambycid species richness than small forests (t = 3.16. P = 0.02), and there was a significant relationship between forest size and cerambycid species richness.


Introduction
Longhorned beetles, or cerambycids, are important species in temperate forest ecosystems, due to their feeding impacts on trees. Many cerambycids feed on dead wood and therefore assist in the decomposition of dead trees in forest ecosystems. Saproxylic cerambycids (dead wood dependent) and other saproxylic beetles are thought to be useful indicators of forest biodiversity 1 . We were interested in testing the hypothesis that larger forests have greater cerambycid species diversity than smaller forests in NW Ohio, a highly fragmented landscape in terms of forest ecosystems.

Methodology
• Three types of traps (Lindgren funnel trap, Intercept Panel trap, and Window trap) were set up in each of 8 forests in northwestern Ohio. 95% ethanol was used to attract beetles ( Figure 1-Figure 3).
• We started collecting beetles in early June, and we continued to collect them until early October (Figure 4).
• We put the traps into 8 different forest areas. Four forests were large (>100 hectares) and four forests were classified as small (<20 hectares).

Changes from Version 1
Upon the Recommendation of referee Patrick Tobin we have provided additional data that shows the relationship between log (species richness) and log (forest area). We have also updated Figure 6 to show if the respective area of each forest could explain the difference in species number. The large R2 value does suggest that larger forests tended to have larger number of cerambycid species. We also estimated the diversity of Cerambycidae using the Shannon Diversity Index value for each of the forests. These

Results and discussion
• Large forests had greater cerambycid species richness than small forests. (Figure 5, Figure 6). • Regression of log (species richness + 1) versus log (forest area + 1) indicated a strong linear relationship between cerambycid species richness and forest size (R 2 = 0.80). (Figure 7). The large R2 value suggests that larger forests tend to have greater cerambycid species diversity than do smaller forests, perhaps due to greater amounts of resources for these beetles in the larger forests compared to the smaller ones.
• Future research should focus on the landscape matrix and degree of isolation of forests, especially isolation of smaller forests.

Total number of individuals (N) 19
Species richness (s) 8

Total number of individuals (N) 12
Species richness (s) 7

Total number of individuals (N) 8
Species richness (s) 5

F1000Research
No competing interests were disclosed. The overall merits of the study, general aspects of the experimental design, and hypothesis tested are interesting and conceptually sound.
The incredible amount of work involved in such a study is also recognized. A primary concern is that only one year of data was collected, which limits the interpretation of the findings. Measuring populations in the field over only one year, from which species richness was estimated, can be subject to annual variation that may lead to over-or underestimates of individuals in any given year. Moreover, some species of Cerambycidae may take more than one year to undergo a generation and thus these species could be undercounted. Regardless, the finding of increased richness with increased forest size confirms prior observations in related diversity studies. Also, the methods applied in this study are sound and thus provide a protocol in future endeavors.
One modification I would like to see in a revised manuscript is that instead of examining differences in richness between two categories (large versus small forests), I would prefer to see richness examined along a continuous measurement (i.e., the size of each forest), assuming that there is variation in sizes among the forests. In looking at Figure 6, I wonder if the respective area of each forest could explain the difference in species number. It also could be insightful to consider estimating diversity using established indices (e.g., Shannon, Simpson), which could help relate your work to other similar studies.
I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
No competing interests were disclosed. Competing Interests: