Name: a method for quantifying foliage-dwelling arthropods
Uploaded: 2019-10-20T13:30:00
Description: Watch this Scientific Journal Video about A Method for Quantifying Foliage-Dwelling Arthropods at JoVE.com

The authors would like to thank the U.S. Department of Agriculture Forest Service for funding this project through USFS Agreement 13-CS-11090800-022. We would like to thank J. Suda, W. Holland, and others for laboratory assistance, and R. Richards for field assistance.

1. Building the sampling device prior to going to the field
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Two necessities of accurately quantifying arthropod communities are relatively high detection probabilities and known or consistent sampling areas. When sampling for arthropods, less than 100% detection probability can be attributed to either individual arthropods avoiding traps or some individuals that were trapped being undetected during processing. Interceptor traps that intercept flying arthropods (Malaise/window traps, sticky traps, etc.) appear to be the most frequently used approach to enumerate arthropod communit...

Terrestrial arthropods play an important role in our ecosystem. In addition to being of scientific interest arthropods can be both detrimental and beneficial to crops, horticultural plants, and natural vegetation as well as provide an important trophic function in food webs. Thus, understanding the factors that influence arthropod community development and abundance is critical to farmers, pest control managers, plant biologists, entomologists, wildlife ecologists, and conservation biologists that study community dynamics and manage insectivorous organisms. Understanding factors that influence arthropod communities and abundances often requires the capture of individuals. Capture techniques can generally be categorized into qualitative techniques that only detect presence of a species for estimates of species range, richness, and diversity, or semi-quantitative and quantitative techniques that allow for an index or estimate of abundance and density of individuals within a taxonomic group.
Qualitative techniques that only allow inference regarding presence of a species or community structure have an unknown or intrinsically low detection probability or are lacking in providing inference regarding detection probability and size of area sampled. Because detection probability with these techniques is low, variability associated with detection precludes adequate precision for inferring how explanatory variables influence arthropod population metrics. Qualitative techniques used to estimate presence include suction sampling1, light traps2, emergence traps3, feeding patterns on roots4, brine pipes5, baits6, pheromone3, pitfall traps7, Malaise traps8, window traps9, suction traps10, beating trays11, spider webs12, leaf mines, frass13, arthropod galls14, vegetation and root damage15.
Alternatively, semi-quantitative and quantitative techniques allow researchers to estimate or at least consistently sample a specified sample area and estimate probability of detection or assume detection probability is non-directional and adequate as to not obscure the researcher&#39;s ability to detect spatial or temporal variation in abundance. Semi-quantitative and quantitative techniques include sweep nets16, suction or vacuum sampling17, systematic counting of visible arthropods18, sticky traps19, various pot-type traps20, entrance or emergent holes21, chemical knockdown22, sticky and water filled color traps23, and branch bagging and clipping24.
Recent anthropogenic-induced changes to climate and disturbance regimes have led to dramatic changes in plant communities, making interactions between plant-community species composition and arthropod communities an active area of study. Understanding how arthropod communities vary with plant species composition is a critical component for understanding the potential economic and environmental impacts of changes to plant communities. Semi-quantitative or quantitative methods of quantifying arthropod abundance with adequate precision to detect differences among species of plants are needed. In this article, we describe a method for indexing foliage-dwelling arthropods that, with reasonable effort, provided adequate precision to identify differences in individual abundance and biomass, diversity, and richness among 5 taxa of trees commonly found in the southeastern deciduous forests of North America25. This approach provided precision adequate for estimating abundance to allow inference as to how changes in species composition of forest plant communities due to anthropic modified disturbance regimes influence composition of arthropods, potentially influencing abundance and distribution of higher trophic insectivorous birds and mammals. More specifically, by using a modified bagging technique first described by Crossley et al.24, we estimated density of surface, foliage-dwelling arthropods and tested the prediction that we would detect differences in diversity, richness, and abundance of arthropods in the foliage of faster growing more xeric species of trees relative to slower growing more mesic species. The goal of this article is to provide detailed instructions of the technique.
We conducted the study on the Shawnee National Forest (SNF) in southern Illinois. The SNF is a 115,738-ha forest located in the Central Hardwoods region of the Ozarks and Shawnee Hills natural divisions26. The forest comprises a mosaic of 37% oak/hickory, 25% mixed-upland hardwoods, 16% beech/maple, and 10% bottomland hardwoods. The SNF is dominated by second growth oak/hickory in upland xeric areas and sugar maple, American beech, and tulip tree (Liriodendron tulipifera) in sheltered mesic valleys27,28.
Site selection for this method will be dependent on the overarching goals of the study. For example, the primarily goal of our original study was to provide insight into how changes in tree community might influence higher trophic organisms by comparing foliage-dwelling arthropod community metrics between mesic and xeric adapted tree communities. Thus, our primary objective was to quantify the arthropod community on individual trees located within the xeric or mesic tree community. We selected 22 study sites along an oak/hickory (xeric) to beech/maple (mesic) dominated gradient using USFS stand cover maps (allveg2008.shp) in ArcGIS 10.1.1. To prevent potential confounding effects, we selected sites using the following criteria: not located in riparian areas, &#8805;12 ha, and located within contiguous upland-deciduous forest habitat (i.e., elevation above 120 m). All sites contained mature trees &#62;50 years old in hilly terrain, thus comprised similar slopes and aspects. While beech/maple site boundaries were distinguished based on the transition of tree communities, oak/hickory site boundaries were identified artificially using SNF cover maps and ArcGIS 10.1.1. All sites were large forest blocks within un-glaciated terrain; their differences in tree species composition were not due to differences in location on the landscape but were representative of past land usage (e.g., clear cuts or selective harvest). We ground-truthed the maps by uploading discrete polygon shapefiles of each study site to a handheld Global Positioning System (GPS) and verifying tree species composition. We randomly selected sampling points (n = 5) at each site. At each point, we sampled three trees from 0600&#8722;1400 hours during 23 May to 25 June 2014. To locate sample trees, we searched outward to a 30 m radius from vegetation points until mature trees (&#62;20 cm d.b.h.) with branches low enough to sample were found. Typically, the three mature trees that represented three of the five genera (Acer, Carya, Fagus, Liriodendron, and Quercus) of interest and were closest to the center point were sampled.

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a method for quantifying foliage-dwelling arthropods

Terrestrial arthropods play an important role in our environment. Quantifying arthropods in a way that allows for a precise index or estimates of density requires a method with high detection probability and a known sampling area. While most described methods provide a qualitative or semi-quantitative estimate adequate for describing species presence, richness, and diversity, few provide an adequately consistent detection probability and known or consistent sampling areas to provide an index or estimate with adequate precision to detect differences in abundance across environmental, spatial, or temporal variables. We describe how to quantify leaf-dwelling arthropods by sealing the leaves and end of branches in a bag, clipping and freezing the bagged material, and rinsing the previously frozen material in water to separate arthropods from the substrate and quantify them. As we demonstrate, this method can be used at a landscape scale to quantify leaf-dwelling arthropods with adequate precision to test for and describe how spatial, temporal, environmental, and ecological variables influence arthropod richness and abundance. This method allowed us to detect differences in density, richness, and diversity of leaf-dwelling arthropods among 5 genera of trees commonly found in southeastern deciduous forests.

We collected 626 samples from 323 individual trees composing 5 tree groups. For estimates of total arthropod biomass per meter of branch sampled, the standard error ranged from 12% to 18% of the mean for the 5 tree groups (Table 1). This level of precision was adequate to detect variation among tree groups and a quadratic change in biomass with date25. This technique provided more precision when estimating guild diversity as demonstrated by the sta...

Watch this Scientific Journal Video about A Method for Quantifying Foliage-Dwelling Arthropods at JoVE.com

A Method for Quantifying Foliage-Dwelling Arthropods

We describe how to quantify leaf dwelling arthropods by sealing the leaves and end of branches in a bag, clipping and freezing the bagged material, and rinsing the previously frozen material in water to separate arthropods from the substrate for quantification.

Terrestrial arthropods play an important role in our environment. Quantifying arthropods in a way that allows for a precise index or estimates of density ...

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