Research Article |
Corresponding author: Adrian Smolis ( adrian.smolis@uwr.edu.pl ) Academic editor: Sonke Hardersen
© 2017 Marcin Kadej, Krzysztof Zając, Adrian Smolis, Dariusz Tarnawski, Katarzyna Tyszecka, Adam Malkiewicz, Monika Pietraszko, Marcin Warchałowski, Radosław Gil.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kadej M, Zając K, Smolis A, Tarnawski D, Tyszecka K, Malkiewicz A, Pietraszko M, Warchałowski M, Gil R (2017) The great capricorn beetle Cerambyx cerdo L. in south-western Poland – the current state and perspectives of conservation in one of the recent distribution centres in Central Europe. In: Campanaro A, Hardersen S, Sabbatini Peverieri G, Carpaneto GM (Eds) Monitoring of saproxylic beetles and other insects protected in the European Union. Nature Conservation 19: 111-134. https://doi.org/10.3897/natureconservation.19.11838
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Presence-only models can aid conservation and management of threatened, elusive species. A MaxEnt model has been developed for the great capricorn beetle (Cerambyx cerdo L., 1758) in south-western Poland and the variables identified best explaining the species’ occurrence on a large scale. Once successfully validated, the model was used to (a) illustrate the expected location of the species’ habitats in the region and in existing Natura 2000 sites (SACs) in S-W Poland and (b) assess the efficacy of the regional network of national protected areas (NPAs) versus Natura 2000 (SACs). Overall, information was gathered on 1025 localities of C. cerdo L., 1758 in Lower Silesia. All the records came from the pedunculate oak Quercus robur L., 1753. The occurrence of the great capricorn beetle in the study region is limited mainly to its eastern part, with a marked concentration in the valleys of the rivers Odra, Barycz and Bystrzyca. The kernel density estimation analysis also showed the high concentration of occupied trees in the north-western part of the region, clearly isolated from the above-mentioned main populations. Although a considerable part of the localities in the study region (74.2%) occurred within protected areas (PAs), their contribution to the species’ conservation varied between the PAs groups. Natura 2000 SACs are the most important PAs, covering more than 30% of the predicted area of suitable habitats in the region and more than 45% of optimal habitats. In total, 384 localities of C. cerdo L., 1758 were found within the cities, most of them (n = 356) in the city of Wrocław. Forty three percent (43%) of the urban localities of the species (n = 165) in the study region are protected within the regional network of protected areas (OPAs), while those unprotected are mainly concentrated in the city of Wrocław (n = 207). Wrocław also includes 17.1% of the area of suitable habitats and 29% optimal habitats of the species in the region outside the protected area network. To preserve C. cerdo L., 1758, forest corridors should be created or restored to bridge the otherwise impermeable gaps revealed by the authors’ model and grant protection to the still largely unprotected area of the Lower Silesian territory. The species conservation programme in the region requires the cooperation of various authorities, not only those dealing with nature conservation, but also local governments, state forest management and flood protection authorities.
Conservation, saproxylic beetles, long-horn beetle, NATURA 2000, Quercus, Lower Silesia
The great capricorn beetle (Cerambyx cerdo L., 1758) is the largest longhorn (Cerambycidae) beetle in Poland and one of the largest beetle species in Europe. Since fairly recently, the species has been under strict legal protection, not only in Poland, but also in most other European countries. It is included in Annex II of the Bern Convention (
As mentioned above, adults of C. cerdo L., 1758 are noticeably large, with body length up to 60 mm. Additionally, the beetle seems to be even larger due to its extremely long antennae which, in males, can be twice as long as the body. Its imposing larvae, which can be longer than adults (up to 100 mm), are xylophagous on different oaks, rarely on other tree species (e.g.
The EU regulations on creating the ecological network Natura 2000, in force in Poland since 2004, have stimulated the interest in the great capricorn beetle in this part of Europe. The requirements imposed then on Poland and pertaining to designation and establishment of areas Natura 2000 and the consequent natural history inventories, have contributed to a better knowledge of the species in various regions of the country. Most of the records from Poland, including its south-western part, date from the boundary of the 19th and 20th century (for review, see
The objective of this paper is to update the knowledge on the distribution of the great capricorn beetle in Lower Silesia as one of the last large refuges of the species, not only on a regional and country-wide scale, but also in Central Europe. The data, combined with climate-habitat variables, were used to create a model based on the algorithm MaxEnt in order to specify: 1) factors which affect the occurrence/distribution of the species in the studied area; 2) present state of habitat fragmentation and areas which are crucial for the species’ protection, considering the “conflicting” areas where the protection may be rendered difficult, for example, urban areas and to propose a strategy for effective conservation and identification of the most important threats and 3) assess adequacy/efficacy of the previous and present nature conservation systems in the context of the species’ preservation in the region.
Regarding the last-mentioned goal, the species is interesting in that, in Poland, it has been under legal protection since 1952 (!) and thus offers a unique opportunity to evaluate the two systems – the one based on nature reserves and landscape or national parks and the one based on habitat protection areas, especially considering that Natura 2000 is subject to criticism not only by that part of the community not interested in nature conservation, but also by naturalists and scientists (
The study region, covering the north-east part of the Lower Silesian province (approx. 9,571 km2), is located in south-western Poland. The altitude ranges from 60 to 703 m above sea level (mean 134 m a.s.l.). The climate is temperate with an average annual rainfall of about 600 mm. According to Corine Land Cover maps (CLC2006; available from: http://www.eea.europa.eu/data-and-maps/data/clc-2006-vector-data-version), the region is dominated by agriculture (~65% of the total area), especially arable land (53.4%). Forests cover 25% of the total area, of which 54% are coniferous forests, 19.4% broad-leaved forests and the remaining 26.6% – mixed forests. Urban areas (class 1.1 in CLC) cover 5% of the total area.
Nationally designated protected areas (NPAs) are represented by 32 nature reserves and 4 landscape parks with a total surface of approx. 81 km2 (0.8% of the region) and 1,014 km2 (7.3%), respectively. In total, the NPAs cover a surface area of 1,021 km2. The Natura 2000 network consists of 39 sites, including 8 Special Protection Areas (SPAs) designated under the Birds Directive (total area of 863 km2 in the region) and 31 Special Areas of Conservation (SACs) under the Habitats Directive (total area of 1,213 km2). All the stand-alone SPA sites were excluded from these analyses as they are only aimed at protecting bird species, while the SACs were included, increasing the total protected surface in the study region by 451 km2. In total, the overall protected areas (OPAs) cover an area of 1,472 km2 (15% of the region).
The data used on the occurrence of the species was collected in 2001–2013 by the staff, co-workers and volunteers of the Laboratory of Invertebrate Conservation Biology and Protection, Wrocław University. Each tree with signs of occupancy by the beetle’s larvae such as holes with a red interior, or on which adults or their remains were found, was regarded as an occupied locality. As there are no other Cerambyx spp. of comparable size in Poland, potential mistakes in the recognition were minimised. Other large cerambycid species like Ergaster faber (L., 1761) are monophagous on Scotch pine Pinus silvestris L., 1753.
The species records were located in the field using a hand-held GPS and then converted into the ESRI shape-file format for later use. The occupied trees were determined at the species level. Each locality was classified into one of the five adopted habitat categories: forests, roadside trees, parks, solitary trees and other. The term ‘solitary trees’ means a single tree situated away from dense tree stands as well as trees loosely distributed in the agricultural landscape. In the case of forest localities, those within the management of the State Forests were distinguished, in the case of roadside trees – those located on flood banks. Besides, all the localities were grouped according to their territorial-administrative appurtenance (municipalities, forest districts) and location within protected areas. In the last case, three forms of protection were considered: nature reserves, landscape parks and Natura 2000 (SACs).
To estimate the current and potential distribution of Cerambyx cerdo L., 1758 in south-western Poland, the kernel density estimation and the ecological niche modelling were used.
Kernel density estimation. – the kernel density estimation (KDE) in the Geospatial Modelling Environment (GME) programme (
Ecological niche modelling. – To predict suitable habitats for C. cerdo L., 1758 in the study region, the ecological niche model (ENM) was developed, using the maximum entropy algorithm implemented in MaxEnt, version 3.4.0. (
To eliminate redundant or spatially auto-correlated occurrence points, the spatially rarefied occurrence data tool in the SDMToolbox in ArcMap (
As environmental variables, 19 bioclimatic layers and an altitude layer from WorldClim (http://www.worldclim.org,
The model in MaxEnt was built using 50 bootstrap replicate runs with the ‘random seed’ option. The records were split into 75% for training and 25% for testing for bootstrap replications. To facilitate model convergence, the maximum iterations were increased to 1,000. A jackknife test was then performed with all data to estimate the weight of each environmental variable in the model. The complementary log-log (cloglog) output was used with habitat suitability on a scale of 0-1, with higher values representing more favourable conditions for the species occurrence. The jackknife tests of variable importance were also used to identify those with important individual effects.
The final model was the average of all runs. To evaluate the performance of the final model, the mean area under the curve (AUC) was used for the receiver operating characteristic curve, calculated from 50 bootstrap models. The AUC ranges from 0 to 1, where a score of 1 indicates perfect discrimination, a score of 0.5 implies predictive discrimination that is no better than a random guess and values <0.5 indicate performance worse than random (
To distinguish between suitable and unsuitable habitat, the 10th percentile training presence (10%TP) threshold was applied. This threshold predicts unsuitable habitat for 10% of the most extreme occurrence records, as these may represent recording errors, ephemeral populations, migrants or the presence of unusual microclimatic conditions within a cell (e.g.
To assess of efficacy of the protected areas for the conservation of Cerambyx cerdo L., 1758 in the region, the contribution of each form of protected areas (PAs) was included to the protection of the known localities, as well as predicting habitats in the region. In addition, to assess the independent impact of the establishment of the Natura 2000 network on the species’ protection, the proportion of the regional network of national protected areas (NPAs) was compared, such as nature reserves and landscape parks alone, in the current network of overall protected areas (OPAs), including Natura 2000 SACs. In the analysis of the contribution to the conservation of the species’ habitats, an assessment was included for both predicted habitats in the whole study region and within the area of probable occurrence of C. cerdo L., 1758, delineated by the isopleth of 95% KDE.
Study region with the network of nationally protected areas (NPAs) and overall protected areas (OPAs).
The environmental variables used in ecological niche modelling of Cerambyx cerdo L., 1758 in south-western Poland.
Name | Description [unit] | Range | Mean ± S.D. | Data source |
---|---|---|---|---|
bio10 | Mean Temperature of Warmest Quarter [°C*10] | 140 – 182 | 174.2 ± 3.6 | Worldclim (www.worldclim.org) |
bio11 | Mean Temperature of Coldest Quarter [°C*10] | - 35 – -8 | -16.3 ± 4.6 | Worldclim (www.worldclim.org) |
bio12 | Annual Precipitation [mm] | 527 – 711 | 554.4 ± 13.1 | Worldclim (www.worldclim.org) |
bio19 | Precipitation in Coldest Quarter [mm] | 78 – 114 | 87.6 ± 5.2 | Worldclim (www.worldclim.org) |
Quercus | Quercus-dominated forests* [%] | 0–95 | 3.8 ± 9.8 | Forest Data Bank (https://www.bdl.lasy.gov.pl/portal/) |
Quercus age | Maximum age of the Quercus-dominated forests* [years] | 0–235 | 34.6 ± 55.1 | Forest Data Bank (https://www.bdl.lasy.gov.pl/portal/) |
core | Interior area of forest patch excluding forest perimeter [%] | 0–100 | 17.9 ± 28.3 | MSPA Pattern Maps (http://forest.jrc.ec.europa.eu) |
edge | Edges – Outside perimeter of forest [%] | 0-24 | 3.2 ± 4.1 | MSPA Pattern Maps (http://forest.jrc.ec.europa.eu) |
islet | Forest islets – disjointed forest patch and too small to contain core [%] | 0-19 | 0.7 ± 1.3 | MSPA Pattern Maps (http://forest.jrc.ec.europa.eu) |
perf | Perforation – Inside perimeter of forest site [%] | 0-25 | 0.9 ± 2.5 | MSPA Pattern Maps (http://forest.jrc.ec.europa.eu) |
In total, information was gathered from 1025 localities of C. cerdo L., 1758 in Lower Silesia; a decided majority (91.4%) were single trees, the remaining cases being groups of 2 to 7 occupied trees. In 67 localities (6.5%), the number of inhabited trees was unknown. All the records came from the pedunculate oak Quercus robur L., 1753. Despite the presence of other oak species in the environs of the localities (native Q. petraea (Matt., 1784) or introduced Q. rubra L., 1753 and Q. cerris L., 1753), no cases of other oaks being inhabited by C. cerdo L., 1758 were found.
The occurrence of the great capricorn beetle in the study region was limited mainly to its eastern part, with a marked concentration in the valleys of the rivers Odra, Barycz and Bystrzyca (Fig.
The KDE analysis also showed the high concentration of the occupied trees in the north-western part of the region, clearly isolated from the above-mentioned main populations of C. cerdo L., 1758 (Fig.
The species’ occurrence in the region, delineated by the isopleth of 95% KDE, largely coincides with the distribution of the highly suitable habitats predicted by MaxEnt modelling (Fig.
Seven variables made more than 5% contribution to the MaxEnt model (Table
The current distribution of Cerambyx cerdo L., 1758 (n = 1025 locations) in south-western Poland and predicted species range delineated by kernel density estimations (KDE) using plug-in bandwidth selection. White lines show the border of 95% KDE. The dashed areas represent the network of overall protected areas (OPAs).
Averaged habitat suitability map for Cerambyx cerdo L., 1758 in south-western Poland (right) and standard deviations of predicted probabilities of occurrence (left) from MaxEnt models. Black-bordered areas show the network of existing protected areas (OPAs), white-bordered show the 95% kernel density isopleth.
Violin plots of the habitat suitability within the 10 areas delineated by kernel density estimations (KDE) for Cerambyx cerdo L., 1758 in SW Poland. White dots indicate medians, box edges represent the inter-quartile range and the grey region and curve show the probability density function.
The relative contributions and permutation importance of the environmental variables to the MaxEnt model. Values shown are averages over replicate runs.
Variable | Percent contribution | Permutation importance |
---|---|---|
bio11 | 27.2 | 43.8 |
bio19 | 16.6 | 18.4 |
Quercus age | 12.7 | 4.3 |
Quercus | 11.4 | 2.2 |
bio12 | 10.3 | 8.8 |
edge | 9.3 | 7.7 |
islet | 6.5 | 2.5 |
bio10 | 3.2 | 7.5 |
core | 2.0 | 1.9 |
perf | 0.9 | 1.8 |
Results of jackknife test of variable importance using training gain. Values shown are averages over 50 replicate runs for each predictor variable alone (left) and the drop in training gain when the variables are removed from the full model (right). Explanation of variable codes: see Table
Although a considerable part of the localities of C. cerdo L., 1758 in the study region (74.2%) occurred within protected areas (PAs), the participation of each group of PAs in the species conservation was different (Table
Most (69.2%) of the 295 known localities of the species outside the protected areas were located in urban areas. In total, 384 localities of C. cerdo L., 1758 were found within the cities, most of them (n = 356) being in the city of Wrocław. Forty three percent (43%) of the urban localities of the species (n = 165) in the study region are protected within the regional network of protected areas (OPAs), while those unprotected are mainly concentrated in the city of Wrocław (n = 207). Wrocław also brings together 17.1% of the area of suitable habitats and 29% of the optimal habitats of the species in the region outside the protected area network. For the probable area of the species’ occurrence (95% KDE), these values are 32.8% and 40.2%, respectively. Wrocław, together with the regional protected areas (OPAs), encompasses more than 91% of the known localities of the species and more than 62% of its optimal habitats in the study region.
Effectiveness of the systems of protected areas (PAs) in protecting Cerambyx cerdo L., 1758 in south-western Poland.
Landscape parks (1014.5 km2) | Nature reserves (80.8 km2) | Natura 2000 SACs (1213.2 km2) | |
Number (percentage) of localities of C. cerdo in PAs | 101 (9.9%) | 43 (4.2%) | 725 (70.7%) |
Area (percentage) of predicted suitable habitats in PAs | 465.7 km2 (20.4%) | 46.9 km2 (2.0%) | 712.0 km2 (31.1%) |
Area (percentage) of predicted optimal habitats in PAs | 110.8 km2 (22.1%) | 8.9 km2 (1.8%) | 226.6 km2 (45.1%) |
Area (percentage) of predicted suitable habitats in PAs within 95% KDE | 301.3 km2 (24.3%) | 44.2 km2 (3.6%) | 466.9 km2 (37.6%) |
Area (percentage) of predicted optimal habitats in PAs within 95% KDE | 87.9 km2 (22.9%) | 8.9 km2 (2.3%) | 185.6 km2 (48.4%) |
Surface areas (km2) obtained by ENM (MaxEnt) within the study region and the 95% kernel density isopleth for Cerambyx cerdo L., 1758 for three different suitabilities covered by national protected areas (NPAs: nature reserves + landscape parks) and overall protected areas (OPAs: NPAs + Natura 200 SACs). Percentages represent the percentage of the total area of the habitat type within the study region and the 95% KDE. Suitability thresholds: optimal ≥ 0.632, 0.632 < moderate ≥ 0.2039, unsuitable < 0.2039.
More than a thousand localities of C. cerdo L., 1758 were recorded confirming that the studied region held numerous localities of the species which is declining in many countries in Central Europe within its north and central range distribution. The fragmentary character of historic data makes it difficult to say with certainty if the results show a satisfactory state of the species’ conservation or only a better knowledge of its distribution (
The results of ENM confirmed the thermophilous character of the species. These results also suggested that there is a relatively higher probability of finding C. cerdo L., 1758 in areas with older oak stands, although a negative impact of core forest areas and positive effect on the percentage of forest edges indicates the avoidance of the forest’s interior.
The concentration of records of C. cerdo L., 1758 in the valleys of the rivers Odra, Bystrzyca and Barycz, besides the favourable thermal conditions compared to the adjacent areas, can also be explained by the presence of relatively numerous deciduous forests, including some with a high proportion of oak, which have been preserved because of the little use of those areas for intensive agriculture and because of planting oak on dykes of fish ponds as in the Barycz valley. Furthermore, the character of such tree stands, in the form of smaller or larger forest islands or rows, seems to suit the species’ requirements. It is noteworthy that the trees in such stands grow far apart, thus enabling a faster growth in thickness and in turn results in thicker bark, both of those parameters being very important for the species (
Despite the passing of more than 20 years since the launch of the System Natura 2000, it still causes great controversies in Poland and in other countries of the European Union (
In the case of invertebrates, including insects, the species lists in Annexes II and IV of the Habitats Directive have also been criticised (
Another argument used by the opponents of Natura 2000 was that it doubled the forms of nature conservation which existed and functioned in all European countries, especially area and species protection. These results do not confirm this objection, but instead show how essential and effective a tool Natura 2000 is in conservation of species such as C. cerdo L., 1758. Within nature reserves and landscape parks which occupy 80.8 km2 and 1014.5 km2, 43 (4.2%) and 101 (9.9%) of the species’ localities, respectively were found. In the network Natura 2000, with its area of 1213.2 km2, 725 localities (70.7%) were found. Great differences between the compared systems, in favour of Natura 2000, also pertain to the area (percentage) of predicted suitable habitats, area (percentage) of predicted optimal habitats, area (percentage) of predicted suitable habitats within the 95% KDE and the area (percentage) of predicted optimal habitats within the 95% KDE (Table
The pessimistic aspect is associated with the possibility of preserving the species in urban areas, as the potential threat to public health from the beetle-occupied trees might result in fallen branches (
On the other hand, the occurrence of the species “close to humans” offers a unique opportunity to educate the society in matters of protection of saproxylic organisms; as a result of its size and interesting biology, the great capricorn beetle is an ideal candidate for an educational subject.
The results not only supplement and update the distributional information on the great capricorn beetle in south-western Poland, but they may also contribute to devising an effective strategy for conservation of this endangered species. The presented data clearly suggest that such a strategy would require the cooperation of many authorities: local governments and forest management institutions such as State Forests, City Green Management (with their communal forests and city parks), water management authorities (floodplains and flood banks) and roads management. The results point to a particular responsibility for the authorities of the largest city within the region Wrocław which holds more than 30% of the localities. Additionally, the largest owner and manager of the forests in Poland, the State Forests, should take an active part in formulating and improving such a strategy.
This study confirms that modelling distributions of the saproxylic species can provide an objective means for the identification of potentially optimal and suitable habitats for their conservation. The analyses on protected area efficacy showed that existing national networks of conservation areas alone are not adequate for preserving species such as C. cerdo L., 1758. Thus, Natura 2000 is the cornerstone on which protection strategies should be built. However, adaptive management plans need to be compiled and then implemented both in each area and their surroundings.
Our sincere thanks go to our colleagues (Grzegorz Bobrowicz, Jakub Józefczuk, Szczepan Polus, Jacek Sarnowski and Tomasz Suchan) for assistance in the field study (collecting data). The research was supported by the Department of Invertebrate Biology, Evolution and Conservation, Institute of Environmental Biology, Faculty of Biological Science, University of Wrocław (project no. 1076/S/IBŚ/2017).
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