Methods
Study sites. Arthropod communities were sampled from pastures (n = 10) located in four states of the Southeastern U.S.: Kentucky (n = 2), Tennessee (n = 2), Alabama (n = 4), and Mississippi (n = 2) (Figure 1). Sampling the foliar and soil arthropod communities occurred three times during the 2018 grazing season (May 1 – 4, July 23 – 28, and Sept. 29 – Oct. 3), while dung community samples were collected only during the July and September sampling dates. Grazing systems had been practiced on pastures for at least 10 years prior to this study, but specific cattle management practices varied amongst pastures.
Sampling procedure. Two sampling areas were established in each pasture, with each sampling area containing three transect lines (45.7 m), for a total of six transects per pasture. The transects within a sampling area were parallel to one another and spaced 15.2 m apart.
Foliar-dwelling arthropods were sampled from pasture foliage at the 22.9 m mark of each of the three transect lines from the first sampling area in each pasture (n = 3 sweep samples/pasture). Vegetation was swept with a 38 cm diameter net, with 25 sweeps occurring perpendicular to each side of a transect line (total of 50 sweeps per transect). All arthropods collected from individual sweep samples were stored in plastic bags containing 3 mL of 70% isopropyl alcohol to preserve and prevent specimens from cannibalism. Samples were kept on ice in the field and returned to the lab, where they were stored at -18°C until arthropod specimens could be separated from loose vegetation in the sample. After which, specimens were preserved in 70% isopropyl alcohol for curation.
Core sampling (10 cm diameter, 10 cm deep) was used to collect the soil and dung communities. Cores were extracted at 7.6 m and 38.1 m on two of the transect lines for soil arthropod community sampling (n = 8 soil cores/ranch). Dung arthropod community cores were taken from the center of randomly selected dung pats found within the pasture borders (n = 5 dung cores/ranch). Age of dung pats ranged from 2 – 5 days old, as this age of pat has peak arthropod abundance and diversity (Pecenka and Lundgren 2018). All cores were kept cool on ice upon extraction from the field until they could be returned to the laboratory (60 h). Once in the laboratory, soil and dung cores were subjected to a Berlese funnel extraction system for 7 d, which ensured each soil/dung core had completely dried and all arthropods had evacuated from the core. Arthropods extracted from cores with the Berlese system were stored in 70% isopropyl alcohol, until they could be identified and cataloged.
Community composition. To characterize the arthropod communities, each specimen from the foliar, soil, and dung samples was identified to the lowest taxonomic level possible. Due to time constraints, no effort was made to identify mites (Arachnida: Acari) beyond the class level, Protura beyond the class level, thrips (Insecta: Thysanoptera) beyond the ordinal level, Symphyla beyond the class level, millipedes (Diplopoda: Julida) beyond the ordinal level, Diplura beyond the family level, nor springtails (Hexapoda: Collembola) beyond the family level. All other specimens were separated to genus or species level. Those for which positive species identifications could not be provided were assigned to a numbered morphospecies. Larvae of holometabolous insects were considered as distinct morphospecies, owing to their discrete differences in ecological function. Morphospecies were assigned to functional guilds, based on knowledge and current hypotheses regarding the ecology of these organisms. We recognized nine non-exclusive guilds: predator, parasitoid, pollinator, herbivore, granivore, coprophage, carrion, livestock pest, and other/unknown.
Voucher specimens are deposited in the Mark F. Longfellow Collection, housed at Blue Dasher Farm (Estelline, South Dakota, USA).