Colonies of Red Wood Ants (Formica s. str.) on the Forest Monitoring Map of the Middle Volga

Red wood ants (subgenus Formica s. str.) have been used as active forest protectors and bioindicators of forest conditions since 1960s

However, a critical lack of exact geographical data made a negative impact on existing situation picture. No information about spatial structure of anthills' complexes was present in form of maps or geobases despite full taxonomic and biological descriptions. This problem provoked a creative search for an efficient method that could provide a detailed ecological map of forest communities. In 2016, scientists of Lobachevsky State University (including the author of the current article) initiated formation of a digital map of the Middle Volga, containing information about anthills and forest conditions in each point of their localization

The given research can be considered as a continuation of previous explorations and as analysis of existing data on a new level. It includes estimation of occurrence frequency, diversity and population density on different ant species of the Middle Volga regions on the GIS base. In "Materials and Methods" the essential analytical algorithms and program components are described. In "Results" the actual picture of spatial ants' population structure is demonstrated. In "Discussion" the results of analysis will be considered in the context of previous explorations. In "Conclusion" the necessity of digital mapping in monitoring of forest communities is estimated and generalized.

The purpose of the current research has been determined as formation and analysis of a detailed map of the Middle Volga. The mentionned map demonstrates the correlation of ants' dispersal with a whole complex of factors, including information about landscape, climatic and geobotanic conditions in explored regions (N. Novgorod, Samara, Saratov regions, republics of Chuvashia and Tatarstan). The data is exported to the map in four layers – lineal layer with administrative borders of Russian regions, point level which demonstrates localization of anthills and two polygonal layers created while spatial analysis (ants' population density map and clusters map showing dominant species in the Middle Volga phytocenoces).

The process of cartographical analysis consists of following steps: formation of a geodatabase in *csv format, export of the base on ArcGIS Online, creation of the colonies` density map, definition of dominant species and the final association of ants` population structure with key factors (landscape type, nature zone, climate, forest type).

As for data about forest growing conditions in the regions (age, density, productivity, quality), it was taken in format of published forest plans from the open sources, such as regional departments of Federal Agency for Forestry, and added to each point of the existing map as detailed information

The main materials had been gathered during 2005-2018 by scientists of Lobachevsky State University as results of field explorations

The method of population density analysis is based on the platform ArcGIS Online. This is a cartographical service created by ESRI CIS company which provide access to basemaps, map formation and analytical operations (e.g. clustering, aggregation, "hot points" analysis etc.)

The statistical analysis of results bases on the StatTech platform. Statistical analysis was carried out using the StatTech v. 3.1.4 (developer – Stattech LLC, Russia). Quantitative indicators were assessed for compliance with the normal distribution using the Shapiro-Wilk test (with the number of subjects less than 50) or the Kolmogorov-Smirnov criterion (with the number of subjects more than 50). In the absence of a normal distribution, quantitative data were described using the median (Me) and the lower and upper quartiles (Q1 – Q3). Categorical data were described with absolute values and percentages. Comparison of two groups in terms of a quantitative indicator, the distribution of which differed from the normal one, was performed using the Mann-Whitney U-test. Comparison of percentages in the analysis of four-field contingency tables was carried out using Pearson's chi-square test (with values of the expected phenomenon more than 10) Comparison of percentages in the analysis of multifield contingency tables was performed using Pearson's chi-square test

The initial map shows geographic patterns of ants' dispersal on the explored territory without association with abiotic factors. It can be seen that most anthills are located in Nizhny Novgorod region and have essentially a homogenous spatial structure – several localities contain anthills of various species which cannot be estimated as complexes in terms of their morphogenetical differences despite short distances between them. Several single anthills are located on the borders of Nizhny Novgorod region and the republic of Mari El and in the Chuvash republic (Figure 1).

Figure 1 - Dispersal of red wood ants (Formica s. str.) in the Middle Volga

DOI:10.23649/JAE.2023.33.13.1

After having constructed an intensity map it can be observed that, despite a broad extension, the population density of most ants inhabiting the Middle Volga is relatively low – complexes can be seen in Arsamasskiy, Krasnobakovskiy, Voskresenskiy, Vetluzhskiy, Tonkinskiy districts of Nizhny Novgorod region. This occurrence can be explained with a higher average age grade of forest in the given districts. As complexes need decades to be formed, they were mostly registered in more «mature» phytocenoses older than 40–60 years mostly belonging to the southern taiga subzone on the north of the region and to the zone of mixed forests with coniferous prevalence in natural reserves, such as Pustynskiy and Kerzhenskiy (Figure 2).

Figure 2 - Density of red wood ants` (Formica s. str.) colonies in the Middle Volga

DOI:10.23649/JAE.2023.33.13.1

As for special structure of Formica s. str. colonies, it should be mentioned that ants inhabiting both single anthills and complexes are dispersed approximately at the same proportion on the full square of explored territory. This pattern can be seen on a cluster map, which demonstrates a significant number of clusters without any strictly defined dominant species. The exception is represented by colonies of the more selective northern wood ant (Formica aquilonia) which tends to show an evident preference for coniferous forests on podzolic and sod-podzolic soils and is known as a typical complex-forming ant species. Another "leader" – red wood ant Formica rufa – seems to have a dominant position in southern and south-eastern deciduous forests, however, it rather inhabits single anthills than complexes and forms smaller clusters (Figure 3).

Figure 3 - Clusters with dominant species of of red wood ants (Formica s. str.) in the Middle Volga

DOI:10.23649/JAE.2023.33.13.2

According to statistical data analysis, main forest condition parameters affecting complex formation were determined as "Age" (young – less than 30 years old, middle-aged – 30–60 years old, and ripening – more than 65 years old), "Density" (groups 0,7, 0,8, 0,9), "Productivity" (II, III, IV productivity classes). After that, their potential correlation with complex formation was checked on the StatTech platform.

As a result of comparing the "Colony type" indicator depending on the "Age" indicator, statistically significant differences were discovered (p < 0,001) (Table 1, Figure 4).

Figure 4 - Analysis of the indicator "Colony type" depending on the indicator "Age"

DOI:10.23649/JAE.2023.33.13.2

Besides that, during assessing the "Density" indicator, depending on the "Colony type" indicator, statistically significant differences were revealed. The area under the ROC curve was 0,867 ± 0,055 with 95% CI: 0,759 – 0,975. The resulting model was statistically significant (p < 0,001). The threshold value of the "Density" indicator at the cut-off point, which corresponded to the highest value of the Youden index, was 0,800. single anthill was predicted with the "Density" value below this value. The sensitivity and specificity of the model were 66,7% and 94,7%, respectively. (Table 2, Figure 5).

Figure 5 - Analysis of the sensibility and specificity of the model depending on the threshold values of the indicator "Density"

DOI:10.23649/JAE.2023.33.13.1

According to the obtained data, during comparing the indicator "Colony typ" depending on the indicator "Productivity", statistically significant differences were revealed (p < 0.001) (Table 3, Figure 6).

Figure 6 - Analysis of the indicator "Colony type»" depending on the indicator "Productivity"

DOI:10.23649/JAE.2023.33.13.1

At the same time, while analyzing the correlation between "Colony type" and "Prevailing tree form" parameters, it was impossible to establish any statistically significant differences (p = 0,075) (Table 4, Figure 7).

Figure 7 - Analysis of the indicator "Colony type" depending on the indicator "Prevailing tree form"

DOI:10.23649/JAE.2023.33.13.1

The cartographical data released in the current research coincide in several questions of population ecology with results of previous explorations got in 2010-2014 and purposed on determination of population structure patterns of Formica ants. According to them, Formica aquilonia tends to inhabit coniferous forests with pine prevalence and forms large complexes rather than single anthills

Besides that, the aspect of ants` widespread in dependence on landscape zoning was examined before by scientists of Lobahevsky state university – they carried out research with an initial hypothesis that anthills tend to form "thickening areas" on the borders of different landscape zones and demonstrate selectivity to dense forests in comparison with open forest-steppes and meadows

Overall, there seem no GIS-methods having been used in previous experience of ant colonies monitoring inside forest communities of the European Russia. This fact highlights the necessity to visualize monitoring data on digital maps and to fill existing information gaps using methods of cartographical analysis.

Finally, it is necessary to empathize that digital mapping deals with problems connected with contradictions in data levels, e.g., shortage of detailed information about size and number of insects in anthills – this data cannot be correlated with detailed information about forest-growing conditions in the given phytocenoses. This inconvenience can be resolved using other forms and mobile applications for data gathering based on geographic information systems, such as Survey123 for ArcGIS or Collector for ArcGIS

According to the results of the given research, red wood ants (subgenus Formica s str.) tend to demonstrate selectivity to climatic and forest growing conditions  (forest type, age, density, productivity), what makes them significant bioindicators for quality monitoring of forest communities (higher population density indicates older phytocenoses of secondary quality which need more protection). These results are not a final stage – they can be regularly updated with new materials of field explorations.

In addition, it was proven that cartographical analysis provides a clearer picture of the ecological situation in regions taking into account "problematic" points with potentially damaged forests or forests under threat of leaf-eating pests. It permits to use geoinformation systems while inventory and estimation of local forestries. This data needs to be published in open access for both scientific communities and regional ecological ministries to determine forest zoning plans and cultivation plans for next years and decades.