Beetle biodiversity response to vegetation restoration of mid-valley riparian woodland in the LRGV of southern Texas.By King, J.E.
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King, J.E. 2015. Beetle biodiversity response to vegetation restoration of mid-valley riparian woodland in the Lower Rio Grande Valley of southern Texas. Unpublished Thesis, Texas A&M University, College Station. viii + 218 pp.
In ecological restoration, habitat managers intervene in a degraded ecosystem to aid its recovery. To assess a restored habitat, one or more characteristics such as biodiversity, ecosystem functioning, and community structure are measured in relation to a reference habitat. While many restoration projects focus on vertebrates, arthropod taxa may be a more informative group, and beetles (Insecta: Coleoptera) in particular are a significant part of most ecosystem functions.
In the four southernmost counties of Texas, the Rio Grande forms a fertile flood plain and delta; however, 98% of the riparian habitat on the Texas side has been cleared for farmland and urban expansion. Recent ecological restoration in some regions of the Lower Rio Grande Valley has consisted of revegetating reclaimed farmland and protecting it from further degradation. Here, an evaluation of the success of the restoration of mid-valley riparian woodland sites based on a survey of beetle communities is conducted at five sites between September 2008 and June 2010. The five sites included three reference sites of primary habitat from coastal brushlands potholes, a sabal palm forest, and a mid-valley riparian woodland, and two restored sites of mid-valley riparian woodland which varied in the age of their restored habitat vegetation. Beat samples and ultraviolet blacklight bucket trap samples were taken once every two weeks, while pitfall traps and Lindgren funnel traps ran continuously and were serviced once every two weeks. The sampling methods employed were designed to capture a wide variety of beetles with different biological characteristics.
In total, 113,490 beetles from 69 families and 977 species and morphospecies
were collected at the five sites. Canthon viridis
(Palisot de Beauvois) (Scarabaeidae) dominated the sabal palm forest while Tropicus pusillus
(Say) (Heteroceridae) was dominant at the other four sites. Calculations of the Simpson’s and Shannon diversity indices and of species richness suggest that beetle species biodiversity in the restored sites is converging with that of the primary forest site. The information presented here should be of use to habitat managers for monitoring current restoration efforts in the Lower Rio Grande Valley and should inform future restoration strategies.
Key words: Lower Rio Grande Valley, beetles, restoration, ecology, Coleoptera
Highlights of overall collection results
In total, 113,490 beetles from 69 families and 977 species and morphospecies were collected at the five sites (Appendices 1-5). 88% of the specimens were identified to species (Appendix 6). At least 31 of the species are believed to be new to science.
As is common in insect surveys, a few taxa dominated with a long ‘tail’ of decreasingly abundant taxa. Heteroceridae (43,184 specimens) and Scarabaeidae (20,163 specimens) dominated this overall survey, and together represented more than the other 67 families combined. Tropicus pusillus
(Heteroceridae) was by far the most commonly collected species (42,019 specimens) and accounted for 37.0% of the total catch (Figure 4).
Overall collection results by collecting method
As described in the methods, four different collecting methods were used: beating, Lindgren funnel traps (LFT), pitfall traps (PFT), and ultraviolet blacklight bucket traps (UV). In order to see the contribution of each collecting method to the overall study, abundance and diversity were measured for each collecting method (Table 1). [snips]
The beat samples collected 6,931 specimens from 387 species.
The LFT collected 9,916 specimens and 541 species.
The PFT collected 26,052 specimens from 338 species.
The UV traps collected 70,591 specimens, 43,179 of which were Heteroceridae. There were 595 species collected by UV.
In this study, 113,490 beetles from 69 families and 977 species and morphospecies were collected and identified over two years in three different biotic habitats and of different successional stages of restoration. Each of the three different biotic habitats were found to have a unique assemblage of beetle species. The Sabal Palm Grove (SPG) beetle community was dominated by dung beetles, the mid-valley riparian woodland (MCM) had a distinct leaf litter beetle community, and the coastal brushland pothole beetle community (LAG) was completely dominated by a variety of water beetles. [snips]
In over 100 years of insect collecting history in the Lower Rio Grande Valley (LRGV), this study is believed to be the first systematic beetle survey in the Sabal palm forest and mid-valley riparian woodland habitats as previous efforts focused on only targeted groups (Schwarz 1896, Knull 1944, Riley and Wolfe 1995). To the author’s knowledge, this study collected more specimens from more species and families than any other forest survey
(Holloway et al. 1992, Burger et al. 2003, Longcore 2003, Kwiatkowski 2011), and this is likely due to using a wider variety of beetle sampling techniques to target a greater range of species than other surveys. That, combined with the ability to identify this hyper-diverse group to species, makes this study a valuable reference for other researchers, and this is shown by the number of studies already published using specimen data collected here (Gimmel 2011, Leavengood Jr et al. 2012, Cline and Skelley 2013).
Further studies should take a functional approach and focus on the major strength of this study: the species level identification of over 100,000 beetles. These names tie these beetles to all of the past, present, and future published research; and with that knowledge one could assign each species to a functional group and/or feeding guild.
Appendix 1-5, Site species lists, ranked by abundance with collecting method (pg. 54-118)
Appendix 6, Complete species list by family, ranked alphabetically with sites found
Appendix 7-11, Site species lists, by family, ranked alphabetically with collecting method (pg. 147-217)
Appendix 12, Identification metrics (pg. 218)
Total # of specimens - 113,490
# of specimens identified to species - 99,842 (88.0%)
Total # of specimens from morphospecies - 13648 (12.0%)
Total # of species/morphospecies - 977
# identified to species - 701 (71.8%)
# identified to morphospecies - 276 (28.2%)
Overview of beetle collecting techniques
employed during this south Texas beetle survey (plus a few shots from outside of s. TX) - Photos by Mike Quinn