Man-made microrefugium of Pterostichus anthracinus

Giorgi Chaladze


An organism can survive, grow, reproduce and maintain a viable population only under certain climatic conditions. However, sometimes viable populations are found outside of favorable climate conditions, which is attributed to local microclimatic conditions. Such small areas with local favorable environmental features, in which small populations can survive outside their main distribution area protected from the unfavorable regional environmental conditions, are called microrefugia. In this paper I describe a man-made microrefugium of Pterostichus anthracinus where a stable population has been observed for 9 years. The importance of microrefugia is discussed.

Keywords: Microrefuigia; Microhabitat; Carabidae; Pterostichus anthracinus.


An organism can survive, grow, reproduce and maintain a viable population only under certain climatic conditions (Begon et al. 2006). However sometimes viable populations are found outside of favorable climate conditions, which is attributed to a local microclimatic conditions (Kavanaugh, 1979). Such small areas with local favorable environmental features, in which small populations can survive outside their main distribution area protected from the unfavorable regional environmental conditions, are called microrefugia (Rull et al., 1988; Rull, 2009) Microrefugia are important for species for re-colonization when surrounding environmental conditions become favorable or as a stepping stones to disperse through hostile habitat for colonization of favorable habitats (Leal, 2001).
Despite the popularity and wide acceptance of microrefugia, empirical examples of them are scarce. For better understanding of formation of modern distribution of species research of microrefugia is essential. Understanding microrefugia will help in optimal planning for challenging climate change (Petit et al., 2008; Rull, 2009).
Modern biodiversity databases provide information about distribution of species; climatic layers are also available. This, in combination with computer algorithms, provides the possibility to understand climatic requirements of species and find modern refugia. P. anthracinus is a hygro and thermophilic species, typical for wetlands (Brose, 2003; Kolesnikov, 2008; Egorov, 1976; Sharova, 1982; Aleksandrovich, 1991; Lindroth, 1992; Neculiseanu and Matalin, 2000). P. anthracinus is a widespread species in western, central and eastern Europe, in north it goes to 600N and south to Caucasus and Iran (Trautner and Geigenmueller, 1987; Reck and Chaladze, 2004; Kryzhanovskij et al., 1995).

Material and methods

The study area is situated in the north-eastern part of Georgia, in the village of Khevsha (lat.: 42.400553°; lon.:  44.688162°), at an elevation of 1486 meters a.s.l. The microhabitat is cow manure piles collected near cow-houses (Fig. 1). Piles are kept intact during winter and in spring moved to nearby gardens. Four such piles were studied. Surrounding agricultural lands, pastures and forests were sampled using hand collecting. Population of P. anthracinus was sampled with non-periodic intensity from 2003 until 2012, using hand sampling (Fig. 2).
Data about the distribution of Pterostichus anthracinus was obtained from GBIF (global biodiversity information facility) database. Data without collection date or collected before 1950 was excluded from the analysis. Data with precision >1000m were also excluded.  In total, 216 unique localities were identified.

Manure habitat

Figure 1 Manure piles, microhabitat of P. anthracinus.

P. anthracinus

Figure 2 P. anthracinus in manure piles.

Information about climate was taken from the WorldClim version 1.4 dataset at a resolution of 30 arcsec (c. 1 km) (Hijmans et al. 2005). For each locality, the following variables were extracted: (1) annual mean temperature,(2) mean diurnal range, (3) isothermality, (4)temperature seasonality, (5) maximum temperature of warmest month, (6) minimum temperature of coldest month, (7) temperature annual range, (8) mean temperature of wettest quarter, (9) mean temperature of driest quarter,(10) mean temperature of warmest quarter, (11) mean temperature of coldest quarter, (12) annual precipitation,(13) precipitation of wettest month, (14) precipitation of driest month, (15) precipitation seasonality, (16) precipitation of wettest quarter, (17) precipitation of driest quarter,(18) precipitation of warmest quarter, (19) precipitation of coldest quarter and (20) Elevation; values was extracted using ArcMap 3.1, special analyst tools.
Distribution model was developed using GARP algorithm  in OpenModeller v1.1 Software (Muñoz et al, 2009).  ¾ of occurrences were randomly selected and used to develop distribution range model. ¼ of occurrences were used to assess precision of model.


Four compost piles (all available) were studied. In each of them, specimens of P. anthracinus were present. Compost piles varied in volume from 1,5 m3  to 4.8 m3.
Presense of P. anthracinus population was recorded every year from 2003 till 2012 in each compost piles. In other habitats, beetles were not recorded.
Distribution by elevation of P. anthracinus varied from -67 to 1067, distribution of occurrences by elevation is shown on fig3.
fig 1

Figure 3 Distribution of occurrences of P. anthracinus by elevation.

The values of six climatic variables in the study area were out of range from known occurrences of P. anthracinus: Mean Diurnal Range, Isothermality, Min Temperature of Coldest Month, Temperature Annual Range, Mean Temperature of Driest Quarter, Precipitation of Warmest Quarter (Table 1).

Table 1. Environmental variable values in known occurrences of P.anthracinus and in the study area.

Environmental Parameter


St. Dev



Study Area

Mean Diurnal Range












Min Temperature of Coldest Month






Temperature Annual Range






Mean Temperature of Driest Quarter






Precipitation of Warmest Quarter













Niche model passed validation test with AUC value 0.94. Study area is sitiated in 49 km, from Nearest predicted range of P. anthracinus (Fig.4).

fig 2

Figure 4 Predicted distribution range of P. anthracinus, Garp Model, AUC value 0.94.


Climate in study area is much colder than in other occurrences known for P. anthracinus. Six climatic variables and elevation were out of range of occurrences.
In the study area, as in most mountainous parts of Georgia, traditional farming is used. Cattle dung during winter is collected within a few meters of cattle houses. Manure is not removed until spring because it is difficult to remove manure in winter with high snow cover and is done using a small sled pulled by a bull. Manure may not be removed for several years, and even when removed, usually large part remains behind.
Cow manure compost never freezes and temperature depending on pile size can reach up to 70 degrees (Kutzner, 2008). It is very rich in biomass and contains a wide variety of fly larvae, earthworms and other arthropods which are a food source for the predatory P. anthracinus and its larvae (Kolesnikov, 2008). These factors provide for the possibility of the thermophilic P.anthracinus to maintain a viable population in cold climate.
Microhabitats suitable for insect survival can be created naturally, for example cryptophilic species of subgenus Oreoplatysma (Ground beetles) live in small deep gorges where snow usually does not melt during summer, because of relief, thus creating suitable microclimate for beetles (Kryzhanovskij et al., 1995). Collempolla Isotomurus alticola lives in cold without any physiological adaptations; species’ cold hardiness is due to the microclimate – a thermally buffered microclimate near running water (Zettel, 1999).
Beetles were recorded only in manure piles but nowhere in other habitats. It is likely that beetles are also found outside compost piles and gardens where compost is moved, but with much less density. This is something to expect because a habitat of a few square meters cannot provide enough migrants for creating detectable density within a several kilometer habitat. Interestingly very close morphologically and ecologically species P. pseudomaceus, is present in most of habitats in study area, however was never recorded in manure piles. Probably manure habitat is too humid for P. pseudomaceus.
Interesting aspect is how small microrefugia could be? As seen in this paper predatory beetle population exists within few square meters in man-made habitat for nine years. Most probably such small population cannot survive thousand years as any isolated population will eventually go extinct (Levins, 1969; Hanski, 1999), however such microrefugia can act as stepping stones providing a suitable habitat during migration. Man-made microrefugia cannot be considered exceptional or rare, because during his agricultural activity, man has created many microhabitats for insects and small mammals (human houses and cattle houses – providing food and microclimate).
One last subject worth mentioning is that occurrences sampled from microrefugia can be misleading during distribution modeling based on climate, especially when working with few occurrences, which is not an uncommon problem for invertebrates.


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