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Faunalpedturbation Effects on Soil Microarthropods in the Negev Desert

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Faunalpedturbation Effects on Soil Microarthropods in the Negev Desert Journal of Arid Environments 73 (2009) 907–911 Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv Faunalpedturbation effects on soil microarthropods in the Negev Desert S. Ukabi a, W.G. Whitford b, Y. Steinberger a,* a The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel b USDA-ARS Jornada Experimental Range, MSC 3JER, New Mexico State University, Las Cruces, New Mexico 88003, USA article info abstract Article history: Soil microarthropod communities in seed-harvester ant-nest (Messor spp.) soils and pits excavated by Received 17 June 2008 porcupines (Hystrix indica) were examined on a hill-slope catena in the Negev Desert to test the Received in revised form hypothesis that animal-produced soil disturbances increase abundance and diversity of soil biota. There 13 January 2009 were significantly fewer arthropods and lower taxonomic diversity of soil microarthropods at the top and Accepted 6 April 2009 mid-slope locations, with no consistent patterns of abundance between cool-wet and hot-dry seasons. Available online 2 May 2009 Some prostigmatids, cryptostigmatids, and other arthropods in ant-nest, porcupine-pit, and undisturbed soils were more abundant in wet than dry seasons at some locations but more abundant in the hot-dry Keywords: Catena season at other locations and sample sites. Seven prostigmatid mite families that were relatively Cryptostigmatids abundant in undisturbed soils were absent or of low abundance in ant-nest modified and porcupine-pit Ecological engineers soils at mid- and low-slope catena locations. The data result in rejection of the hypothesis. However, the Prostigmatids significant effects of topographic position on the catena on soil microarthropod communities emphasize Soil mites the importance of examining broad spatial patterns and temporal variation before making generaliza- Taxonomic diversity tions about the effects of ecological engineers on arid ecosystem structure and function. Taxonomic richness Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction studies are required in order to understand the response patterns if such patterns really exist. It is possible that there are no general Faunal pedturbation (soil modification by animal activity) has patterns of responses to faunal pedturbations related to topo- been reported to increase soil nutrients, increase water infiltration graphic position. Soil nutrient concentrations vary temporally with rates, increase plant biomass production, and to change species organic matter inputs, soil water content, annual plant growth, and composition of the plant communities that develop on the modi- activities of soil microflora, micro and mesofauna (Tongway and fied soils (Whitford and Kay, 1999; Whitford, 2000). Faunal ped- Whitford, 2002). It is, therefore, probable that the effects of faunal turbations are frequently cited as examples of ecological pedturbations will vary among seasons and among years. As with engineering (Jones et al., 1997). Most studies of the effects of faunal patterns of spatial variability, temporal variation in the effects of pedturbations have been limited both spatially (single site) and faunal pedturbations require considerably more data before temporally (single sample date). A study of the effects of seed patterns can be discerned. harvester ant (Pogonomyrmex rugosus) nests on soil nutrients and The frequently reported effects of faunal pedturbations on soil annual plant communities on a Chihuahuan Desert watershed nutrients and plant communities suggest that these soil modifica- found that soil nutrients and annual plant production increased in tions have affected processes mediated by soil microflora and micro- nest-modified soils on low-slope locations on the watershed but mesofauna. In arid ecosystems, certain taxa of soil microarthropods not on the steeper erosional surfaces (Whitford and DiMarco, 1995). (mesofauna) were found to affect nitrogen immobilization–miner- A recent study of the effects of long-lived ant nests on a desert alization rates, rates of decomposition, and the abundance of free- watershed reported different effects on annuals associated with living nematodes (Santos and Whitford, 1981; Santos et al., 1981; P. rugosus nests at different locations on a low-slope catena and Parker et al., 1984). One study reported higher density and abun- differences at the same locations in other seasons (Whitford et al., dance of soil mesofauna in soils modified by the nests of seed 2008). Therefore, the effects of faunal pedturbations appear to vary harvester ants Messor spp. (Boulton et al., 2003). In arid ecosystems, among topographic locations on watersheds or catenas but more microarthropod abundance and diversity increase with increased amounts of plant litter (Santos et al.,1978). This suggests that faunal pedturbations that result in concentration of plant litter should * Corresponding author. Tel.: þ972 3 5318571; fax: þ972 3 7384058. result in increased abundance of microarthropods and in differences E-mail address: [email protected] (Y. Steinberger). in composition of the microarthropod community. 0140-1963/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2009.04.001 908 S. Ukabi et al. / Journal of Arid Environments 73 (2009) 907–911 In the Negev Desert, the Indian crested porcupine, Hystrix indica, University. The soil samples were sieved (2 mm mesh size) and and seed harvesting ants, Messor spp., are sympatric agents of soil stored at 4 C until biological and chemical analysis. disturbance. H. indica digs large, discrete, elongated pits in the soil when foraging for below-ground plant storage organs (Shachak 2.3. Laboratory analysis et al., 1991). Pits produced by H. indica serve as traps for wind and water transported plant litter and seeds (Alkon, 1999). Messor spp. Soil moisture was measured gravimetrically for each fresh soil ants transport soil from depths of 2 m or greater and deposit the sample by drying in an oven at 105 C for 24 h. Total organic soil near the nest entrance (Steinberger et al., 1992). They also carbon in soils was measured for each soil sample by the method transport seed husks, awns, and other plant debris from the nest of Rowell (1994). and deposit that material in chaff piles around the nest entrance. At each sampling period, 100 g soil was placed in a modified Because these animals produce disturbances that result in organic Tullgren funnel to extract microarthropods (Santos et al., 1978), prior material accumulations and which may affect water infiltration and to chemical analysis. The total number of microarthropods was soil porosity, we hypothesized that perturbations produced by counted and representatives of the different microarthropods were these taxa would result in increased abundance and diversity of soil mounted on slides in Hoyer’s medium. Mites were identified to family microarthropods. We also hypothesized that the effects of these using the keys in Krantz (1978) and some cryptostigmatid mites were perturbations would be greater in run-on locations on a catena identified to genus using reference collections made by J.A. Wallwork. than on upper-slope, run-off locations. 2.4. Statistical analysis 2. Materials and methods All data were subjected to analysis of variance using an SAS 2.1. Study sites model (two-way ANOVA, (SAS Inst, 1988)). Differences obtained at a level of p < 0.05 were considered significant. Duncan’s and Tukey’s The study site was located at the M. Evenari Runoff Research multiple range tests were used to evaluate differences between Farm (30470,34360E) Avdat, a watershed of the highland Negev separate means (Sokal and Rohlf, 1969). Taxonomic diversity of Desert, Israel. The area has a temperate desert climate, with cool microarthropods of ant nest, porcupine pit, and reference soils at the winters (5–14 C range in January) and hot, dry summers (18–23 C four topographic locations on the catena was calculated by in June). The elevation of this site is approximately 600 m above sea the Shannon–Weaver diversity index H. H ¼Spiln pi, where pi is level, with a multi-annual average rainfall of 89.5 mm (Avdat the proportion of the ith taxon (Shannon and Weaver, 1949). Station), ranging from 24.0 mm in an extreme drought year to 183.3 mm in a wet year (Evenari et al., 1982a,b). The rainy season 3. Results usually begins in October and ends at the end of April, with most of the rainfall occurring in scattered showers between December and 3.1. Soil water content and organic carbon February. An additional moisture source comes from approximately 35 mm of dew, which occurs heavily during an average of 210 There were no differences in soil moisture among the catenary nights in late summer and autumn. The annual evaporation rate is locations or animal modified soils and reference soils during the 2615.3 mm (Evenari et al., 1982a). Soils at the study site are period of the study. Soil water content of 11.3–12.0% in January composed of aeolian loess deposits. The loess soils are alkaline and 2005 and of 4.5–7.4% in March 2005 was higher (p < 0.05) than on exhibit low salinity in the upper layer, which increases with depth, all other sampling periods in which soil water content varied as well as a horizon of gypsum accumulation (Dan et al., 1973). between 0.5 and 3.0%. There were no differences in percent of The study site is a hill-slope catena consisting of four distinct areas organic carbon among catenary positions, undisturbed ant nests that differ in run-off, run-on characteristics. The catena consists of hill and porcupine-pit soils. Percent of organic carbon varied between top, mid-slope, low-slope, and run-on basin. The soil microarthropod 2% and 4% for the 2005–2006 sample dates and between 0.2 and communities of harvester ant (Messor spp.) nest-modified soils and of 1.0% for the 2004 sample dates.
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