DOI: 10.5061/dryad.fqz612jrm
title: Ant-hill heterogeneity and grassland management

description: 1. In many grasslands, some ants act as ecological engineers to produce
 long-lasting soil structures which have a considerable influence on the
 patterns and dynamics of plant, vertebrate and invertebrate species. They
 promote species richness and diversity. 2. The yellow meadow ant, Lasius
 flavus, is the most abundant allogenic ecological engineer in grazed
 European grasslands, producing vegetated long-lasting mounds. Its ratio of
 influence to biomass is remarkably high. Grassland restoration projects
 frequently attempt to re-introduce grasslands on abandoned arable fields.
 When this ant does not colonise naturally it should be introduced. It
 probably limits the abundance of grasses in a similar manner to
 hemi-parasitic plant species. 3. Ant-hills make a distinctive contribution
 to grassland heterogeneity. Measurements on mounds in a single grassland
 over 45 years document the dynamics of the same 200+ ant-hills in volume,
 surface area and basal area. As the mounds aged they increased in size and
 took over a higher proportion of the grassland surface. Occupied mounds
 continued to grow, abandoned mounds decreased in volume and some
 disappeared entirely. 4. Four plant species favoured by the soil heaped by
 the ants were also monitored. Two woody perennials grew up through heaped
 soil and two short-lived species colonised its surface. As the mounds
 became occupied some of these species significantly increased, and when
 they were abandoned some decreased. 5. In a grassland, the ant-hill
 population provides a fluctuating subset of plant and animal species which
 are characteristic of temporary habitats. This seems likely to reduce the
 rate of local extinctions which might otherwise result from fluctuations
 in grazing pressure. In conservation settings, ant-hills should be
 introduced or maintained where possible, and considered in planning
 grassland maintenance and management.Minhyuk Seo
description: The progress of a single ant-hill population was measured by the
 same observer in 1970, 2007 and 2015 in the same calcareous grassland at
 Beacon Hill, Aston Rowant National Nature Reserve (UK NGR SU727972,
 230-244 m altitude) at which the vegetation on the ant-hills has been
 investigated (e.g. King, 1977a, 1977b, 1977c, 2007). This plot (Figure 1)
 is described in detail in King 1977b. It was last ploughed about 1904,
 although it was a rabbit farm from 1935-1954 (local farmer, per sonal
 communication, 2009). The size of every fifth ant-hill in the
 northern-eastern half of this field, a total of 206, was measured in 1969.
 In 2007, the 333 ant-hills in 800 m<sup>2</sup> of this area
 were all mapped and their volumes estimated. The same area was sampled
 once more in 2015, when each individual ant-hill mapped in 2007 was
 measured again, without reference to the 2007 data.   On each ant-hill, two
 measurements were recorded of its horizontal diameter and four of its
 height according to established methodology (King, 1977b, 1981a).  To
 calculate volumes and surface areas, ant-hills were regarded as spherical
 caps.  If the average radius of the base of the cap is a cm, and its
 average height is h cm, then the volume of the ant-hill is
 <b>π</b>h (3a<sup>2</sup> +
 h<sup>2</sup>)/6000 Litres, and its surface area is
 <b>π</b>(a<sup>2</sup> +
 h<sup>2</sup>)/10000 square metres. The percentage cover of
 bare soil was estimated by eye. The presence or otherwise of a
 <i>Lasius flavus</i> colony within the mound was recorded on
 each occasion. In fewer than 3% of cases some individuals of
 <i>Lasius nig</i>er or <i>Myrmica spp</i>. were
 present. The percentage cover of <i>Thymus drucei</i> and
 <i>Helianthemum chamaecistus</i> was recorded by eye and the
 numbers of flowers of <i>Arenaria serpyllifolia</i> and
 <i>Cerastium fontanum</i> were counted. The calculated surface
 areas of each mound allowed the areas of bare soil, <i>T.
 drucei</i> and <i>H. chaecistus</i> to be estimated. The
 non-parametric Wilcoxon signed-ranks test for matched pairs (Sokal
 & Rohlf, 2012) was used to compare the 2007 and 2015 data for the
 same ant-hills because the underlying distribution pattern of the data was
 sometimes difficult to transform to normality.  Plant nomenclature follows
 Stace (2019).