A Test for a Differential Colonization and Competitive Ability in Two Generalist Predators

Abstract

Spatial subdivision of the landscape can reduce the intensity of interspecific interactions, whether they be predation or competition. Recent models examining the ways in which spatial pattern in the landscape will influence the outcome of species interactions assume a trade-off between colonization ability and competitive ability in the interacting species. We tested for differential colonization and competitive ability in two interacting species of wolf spider (Hogna helluo and Pardosa milvina) which co-occur in agricultural and early successional habitats in the eastern USA. We conducted our research in replicated experimental soybean plots in which we created islands of enhanced habitat by supplementing natural litter and enhancing weed growth. Our experimental manipulations were repeated once for each of the two spider species: (1) spiders added, (2) prey attractants (composted vegetable waste) added, (3) spiders and prey attractants added, and (4) one control, for a total of eight subplots. We replicated the experiment six times, three times each in conventionally tilled fields and conservation tilled fields. We censused these plots at the end of the summer and found that conspecific addition significantly elevated numbers of one species (H. helluo) but not the other (P. milvina). These findings were consistent with our predictions that H. helluo is limited in colonization ability when compared to P. milvina. The addition of prey attractants significantly elevated numbers of both species, but the effect was far stronger for the superior colonist (P. milvina). This indicates that P. milvina is able to track resource abundance (both habitat structure and prey), a trait correlated with colonization ability. We found no strong evidence for a negative effect of H. helluo addition on numbers of P. milvina, as would be predicted if H. helluo strongly competed with or significantly preyed upon P. milvina. Body condition of P. milvina was lowest in subplots with higher numbers of H. helluo, indicating that H. helluo may have influenced the foraging success of P. milvina. We also found a strong and unexpected effect of the context of the plots (background tillage regime) on numbers of P. milvina, with there being approximately twice the P. milvina in the subplots in conventionally tilled fields.

Augmentation of soil detritus affects the spider community and herbivory in a soybean agroecosystem

“…We conducted this research in six 0.42 ha soybean fields randomly selected from an array of 12 fields located at Miami University's Ecology Research Center (ERC: 5 km N of Oxford, Butler County, OH, USA) during the summer of 1996. Each field measured 60 × 70 m with a 15 m mowed grass border that separated it from others and the surrounding habitat (Kemp & Barrett, 1989;Marshall et al, 2000). Half of the soybean fields had been managed using conservation tillage (otherwise known as no-till) practices since 1994.…”

“…These plots were separated from one another by a minimum of 10 m and were at least 16 m from the edge of the field. Because spider density is known to respond to plant density (Rypstra et al, 1999;Langellotto & Denno, 2004) and the depth and complexity of the litter layer (Uetz, 1976;Bultman & Uetz, 1982), we attempted to make the plots as homogeneous as possible by planting 3600 ml of wild bird seed mix and covering the surface with 5 cm of wheat straw (see Marshall et al, 2000). The plots were isolated from the rest of the field by a 3-m tilled buffer strip.…”

“…We enhanced the detrital community in two plots in each field using a modification of the protocol developed by Chen and Wise (1997) (see Marshall et al, 2000). We collected discarded fruit and vegetable matter from Miami University's kitchens and composted it.…”

Assessment of Potential Predation Costs of Male Decoration and Courtship Display in Wolf Spiders Using Video Digitization and Playback

“…Because of its abundance and large mass (ca. 200 mg), H. helluo is thought to be an important intraguild predator (Marshall and Rypstra, 1999;Marshall et al, 2000;Persons et al, 2001). We collected H. helluo in September 1996 from a deciduous forest edge microhabitat adjacent to an open grass field in Mount Airy Forest, Cincinnati, Hamilton County, Ohio.…”

The effects of habitat and spatial features of wetland fragments on the abundance of two rallid species with different degrees of habitat specialization

“…Patch quality may be a further determinant of species' occupancy and turnover rates (Summerville & Crist 2001, Thomas et al 2001, Fleishman et al 2002, Bennett & Saunders 2010. The response to habitat quantity, quality, fragmentation and isolation differs between species, with the relative importance of these factors depending on species traits (Hokit et al 1999, Marshall et al 2000, Johansson & Ehrlén 2003. Most specialized and low-dispersal species show distinctive ecological requirements and are often sensible to variation in the aforementioned factors, while species with broader niches and high mobility are often less affected by environmental traits and occur over a broader range of combinations of isolation, habitat types and features.…”