DOI: 10.5061/dryad.5dv41ns8c
title: Local and landscape environmental heterogeneity drive ant community structure in temperate semi-natural upland grasslands

description: Environmental heterogeneity is an important driver of ecological
 communities. Here, we assessed the effects of local and landscape spatial
 environmental heterogeneity on ant community structure in temperate
 semi-natural upland grasslands of Central Germany. We surveyed 33
 grassland sites representing a gradient in elevation and landscape
 composition. Local environmental heterogeneity was measured in terms of
 variability of temperature and moisture within and between grassland
 sites. Grassland management type (pasture vs. meadows) was additionally
 included as a local environmental heterogeneity measure. The complexity of
 habitat types in the surroundings of grassland sites was used as a measure
 of landscape environmental heterogeneity. As descriptors of ant community
 structure, we considered species composition, community evenness, and
 functional response traits. We found that extensively grazed pastures and
 within-site heterogeneity in soil moisture at local scale, and a high
 diversity of land cover types at the landscape scale affected ant species
 composition by promoting nest densities. Ant community evenness was high
 in wetter grasslands with low within-site variability in soil moisture and
 surrounded by a less diverse landscape. Fourth-corner models revealed that
 ant community structure response to environmental heterogeneity was
 mediated mainly by worker size, colony size, and life history traits
 related with colony reproduction and foundation. We discuss how withinsite
 local variability in soil moisture and low-intensity grazing promote ant
 species densities, and highlight the role of habitat temperature and
 humidity in affecting community evenness. We hypothesize that a higher
 diversity of land cover types in a forest-dominated landscape buffers less
 favorable environmental conditions for ant species establishment and
 dispersal between grasslands. We conclude that spatial environmental
 heterogeneity at local and landscape scales plays an important role as a
 deterministic force in filtering ant species and, along with neutral
 processes (e.g. stochastic colonization), in shaping ant community
 structure in temperate semi-natural upland grasslands.
description: Ant survey and nest density
 calculation was based on “Seifert, B. (2017). The ecology of Central
 European non-arboreal ants – 37 years of a broad-spectrum analysis under
 permanent taxonomic control. Soil Organisms, 89(1), pp. 1–67. Dataset
 collection is provided in detail in the article's main text and
 appendix.  <strong>Ant
 survey:</strong> The procedure consists of direct localization of
 workers and nests within a spatially nested scheme covering three levels
 of search effort in a specific area: an intensive scrutiny (S-) search
 performed on soil and vegetation within a smaller area (S- sampling area);
 a quick (Q-) search on ground surface performed within a larger area (Q-
 sampling area); and a spot inspection (SI-) in the most promising habitats
 for nests in the surroundings of the Q-areas. The S- search aims to detect
 nests of small species with hidden nests and small territories, while the
 Q- search reflects realistic nest densities of larger species with lower
 nest densities but larger territories. The SI sampling allows discovery of
 nests of rare species such as social parasites of
 <em>Lasius</em> or <em>Formica</em> genera. We
 employed fixed dimensions of 64 m<sup>2</sup> for S- sampling
 areas and 400 m<sup>2</sup> for Q- sampling areas, while SI
 areas covered c. 900 ± 82 m<sup>2</sup>. The combination of
 these three levels constituted a sample unit referred to hereafter as
 Seifert-plot. Time expenditure for ant searching in S- sampling areas
 varied from 30 to 60 minutes depending on the vegetation structure, and up
 to 180 minutes for the entire Seifert-plot. Recording of foraging workers
 and nests was performed sequentially from S- to Q- and SI-areas, and up to
 10 workers per nest were collected after finishing each sampling area.
 Depending on the grassland size and accessibility, one to three
 Seifert-plots were established per grassland site. All Seifert-plots were
 searched between 08:00 and 18:00 hrs local time in August 2017.
 <strong>Nest density
 calculation (Integrated nest density calculation): </strong>Nest
 abundance from each Seifert-plot component (S-, Q-, and SI-) was combined
 into a final integrated species-specific density (ISSD) which represents
 the nest density of a species within 100 m<sup>2</sup>
 (Seifert 2017). The ISSD per species is calculated as the sum of nests
 found in the S-, Q- and SI- sampling areas divided by the pseudo-area of
 the “recording group” (RG) to which a particular species belongs (Eq. 1).
 The RG is a generalization of how perceptible a nest is accordance with
 the ant species biology. The assignment of a species into a given RG
 describes the probability of finding a nest in each sampling level (S-,
 Q-, and SI-), and such probability is determined by nest's position,
 type, size and density. Based on almost four decades of research on
 Central European ants, Seifert (2017) defined five RGs (i-v) ranking from
 lowest to largest perceptibility. The pseudo-area is calculated for each
 RG separately and provides a measure of the total intensity of
 investigation on a Seifert-plot per RG. This parameter may be understood
 as the area equivalent needed in a specific RG to find the sum of nests
 recorded by S-, Q- and SI-search. The pseudo-area is defined as the sum of
 all nests detected in all search levels divided by a fixed value per RG,
 the recording-group-specific total density or FRSD (Eq. 2). The FRSD is
 the number of nests of a specific RG expected to occur in 100
 m<sup>2</sup>, based on the total number of nest of all
 species occurring in such RG and weighted by the sampling area (Eq. 3).
 The sampling area employed in Eq. 3 is subedited to the RG (See Seifert
 2017 for more details). As a short example, let us say that we are interested in calculating nest densities of <em>M. rubra</em> per grassland site. Our estimations would be focused on the RG iii (common grassland species; Seifert 2017), and FRSD and pseudo-area would be based on S- sampling area (64 m<sup>2</sup>). Thus, in an hypothetical community of five species and 11 nests resulting from a Seifert-plot with S= 3 nests (2 <em>M. rubra</em>), Q= 4 nests (1 M<em>. rubra</em>) and SI= 4 nests (0 <em>M. rubra</em>), the FRSD and pseudo-area will be 4.688 nests/100 m<sup>2</sup> and 2.347 m<sup>2</sup> respectively, and the integrated species-specific density (ISSD) for <em>M. rubra</em> will be 1.278 nests/100 m<sup>2</sup>.
description: Microsoft Excel - LibreOffice Calc