Biodiversity – economy or ecology ? Long-term study of changes in the biodiversity of aphids living in steppe-like grasslands in Central Europe

This paper examines the changes in the species composition of aphids living in dry calcareous grasslands in Central Europe over a 25-year period. To the best of our knowledge, this is the fi rst analysis of this type in the world that takes into account both previous and current data on species richness as well as groups of aphids that are distinguishable on the basis of biological and ecological criteria such as host-alternation and feeding types, life cycle, ecological niche, symbiosis with ants and their ecological functional groups. Over the period of more than 25 years, there has been a signifi cant decrease in aphid α-diversity, from 171 to 105 species. The gain, which is in species not previously recorded, was 17 taxa. The loss of biodiversity occurred despite the fact that these habitats are protected and are valuable regional biodiversity hotspots. The losses are mostly related to intensive human activity in adjacent areas, which, unfortunately, has resulted in the isolation of these small, protected environmental islands by the removal of ecological corridors. Since, as is shown in this study, the frequencies between individual biological and ecological groups of aphids have been retained, it would be possible to restrict this loss of biodiversity if appropriate actions are taken.


INTRODUCTION
The fragments of steppe-like grasslands that still occur in Central Europe are characterized by a high richness of plant and animal species, especially small arthropods.This is why they are also called "regional biodiversity hotspots" (Cremene et al., 2005) and are protected as nature reserves (CRFOP, 2010) or included in the Natura 2000 European network (European Commission, 2013).Unfortunately, strong human interference in recent decades has caused the majority of these fragments of grassland to become smaller and smaller.At present, they exist only as small isolated "habitat islands", and this may have resulted in biodiversity loss (Burkey, 1989;Collinge, 2000;Krauss et al., 2010).
Therefore, an important question is whether such an unfavourable process really occurs in these protected habitats.It is only possible to answer this question if we have the appropriate comparative data.This is possible for the presented group of insects as we have complete historical data.To fully identify the losses in terms of biodiversity over a period of over 25 years, both the former and current species richness of aphids were analyzed, as well as groups of aphids that were distinguished on the basis of specifi c biological and ecological criteria.This made it possible to EFG-β: generalist opportunists (G) that are polyphagous and oligophagous (FT-β), mainly heteroecious (HA-β) and holocyclic or anholocyclic (LC-α or LC-β) species of aphids.

Statistical analysis
Since the data was binary, we applied an indirect nonlinear ordination method, i.e. non-metric multi-dimensional scaling (NMDS), to determine the community composition at the sites studied (Minchin, 1987;Oksanen et al., 2016).Bray-Curtis distance measures were used to construct the dissimilarity matrix.
In order to determine whether there are signifi cant differences in species richness between the historical and current data, a Paired Sample T-test (data was normal, Shapiro-Test: p > 0.05) was used.
In order to determine differences in the frequencies in the functional groups between historical and current data, contingency tables (G test) were used.
All statistics were performed using the R Language and Environment (R Core Team, 2015, package vegan).

Losses and gains in species diversity
The data includes 188 species of aphids that occur in calcareous grasslands (Table 1), which constitutes as much as 12.5% of the aphid fauna in Europe.Of these, 171 taxa were found previously and only 105 currently.Thus, 66 species have been lost.Losses were also recorded in different regions in this study, a loss of 54 species (from 106 to 52) in the Nida Basin and 38 (from 120 to 82) in the Częstochowa Upland.The greatest increase was recorded at Góra Brodło (site D -as many as 43 species) and the lowest at Krzyżanowice (site A -only 4) (Table 1).During the current research, a slight gain of 17 species was recorded, which were not previously recorded in the calcareous grasslands at these sites.More species were recorded in the Częstochowa Upland (12 -out of which only eight here) and fewer in the Nida Valley (seven -out of which only three here).The largest number of new species (12) was recorded at Wzgórze Zamkowe (site E) and the lowest at Krzyżanowice (site A) and Skowronno (site B), with fi ve species at each site (Table 1).
The losses of species were recorded for all the groups of aphid species distinguished and analyzed.The greatest losses were recorded for the holocyclic species (group LC-β -76 species) and monoecious species (HA-α -70), which live above ground (EN-α -55) and are not attended by ants or only sometimes visited by ants (SA-β -50), which, at the same time, are specialists with a narrow host range (SE-α -46) (Table 1).

Changes in species richness and composition
The average species richness during the course of this study decreased signifi cantly at the sites studied (t = -3.8197,p = 0.01878) from 65.6 ± 23 to 41.4 ± 16.2.The NMDS analysis revealed that these sites varied over time and the gradient in species richness and differences in species compositions changed along the NMDS2 axis (Fig. 1).Considering the functional structure, there were no signifi cant differences in the frequency of the different biological and ecological groups of species in the histori-Częstochowa Upland; the complete material comes from the years 1988-1990(Hałaj, 1996c;;Hałaj & Wojciechowski, 1996).

Current data
Material from all fi ve sites was collected in 2011-2012(Osiadacz & Hałaj, 2015) and supplemented by the authors in 2015-2016.

Insects collected
In all cases (in both the historical and present study), aphids were collected using standard methods (by visual inspection of all host plants in an area of approx.50 m 2 , at approximately twoweek intervals during the entire vegetative seasons); next, the aphids were prepared (Hałaj & Osiadacz, 2016) and identifi ed using specialist keys, a list of which is presented in the paper by Blackman & Eastop (2016).Historical specimens are deposited in the collection of the Museum and Institute of Zoology of Polish Academy of Sciences in Warsaw and the Department of Zoology of the University of Silesia in Katowice, while more recently collected specimens are deposited in the collection of the Department of Entomology and Environmental Protection of Poznan University of Life Sciences.

Biological and ecological criteria
In addition to the strictly qualitative comparisons (species composition), the aphids were also compared in terms of biological and ecological criteria.
Host-feeding types (Heie, 1980;Hałaj & Osiadacz, 2016): FT-α (monophagous and narrow oligophagous), species with a narrow host range that are trophically connected with one species or one genus of host plants; FT-β (oligophagous and polyphagous), species with a broad host range, which includes the remaining aphids.

Ecological niche (Blackman & Eastop, 2016):
EN-α: aphids that feed on the aboveground parts of plants, i.e. stalks, leaves, infl orescences; EN-β: aphids that feed on ground level and underground parts of plants, i.e. root collars and roots.

Hostfeeding
Life cycle

Changes in biodiversity
Studies in recent years have shown that there have been dramatic decreases in biodiversity (e.g.Butchart et al., 2010;Boyle & Boyle, 2013;Burns et al., 2014;Kunz, 2016).Our study reveals that this happens not only in well-studied groups of insects, e.g.butterfl ies, beetles and Hymenoptera etc. (e.g.Stewart et al., 2007;Nowacki & Wąsala, 2008;Banaszak & Ratyńska, 2014;Senapathi et al., 2015;Pozsgai et al., 2016), but also in suctorial phytophagous insects, which are rarely thought of in terms of biodiversity.Our analyses have shown a decrease in the α-diversity of aphids over a period of more than 25 years at all the sites studied.Although this applies to aphids in all of the distinguished biological and ecological groups, the most worrying is the decrease in the number of specialists (SE-α) along with a simultaneous increase in the number of generalists (SE-β), which leads to "biotic homogenisation" (Fig. 1).Similar changes are reported in other dry grass-lands studied (Osiadacz & Hałaj, 2016), which result in the "synanthropisation" of communities.This is most marked at Wzgórze Zamkowe (site E).Many specialist species are no longer recorded there, e.g.those of the genera Aphis and Uroleucon.Coloradoa spp., Pleotrichophorus spp.and Xerobion judenkoi also no longer occur there although their host plant (Artemisia campestris) is as abundant as previously (Urbisz, 2008).This confi rms the thesis put forward by Osiadacz & Hałaj (2015).It is also reported in other types of habitats, e.g.bogs (Hałaj, 1991(Hałaj, , 1993) ) and coniferous and broad-leaved forests (Hałaj & Wojciechowski, 1997;Durak & Wojciechowski, 2005) that the presence of host plants is not a suffi cient condition for the occurrence of a specifi c species of aphid.The number of generalists, on the other hand, is associated with the increase in synanthropic plants that colonize these habitats.This also confi rms another thesis that changes in the composition of an aphid community are closely related to changes in the composition of plant assemblages (which is also recorded for other invertebrates: Schaffers et al., 2008), which indicate important changes in the habitat (Osiadacz & Hałaj, 2016).On a much smaller scale, such a phenomenon was recorded at Wzgórze Zamkowe (sites E) and Góra Brodło (site D).As both sites are currently situated in a strongly developing tourist area in the Częstochowa Upland area, it is concluded that the changes in biodiversity are associated with tourism (Hall, 2010).However, despite the fact that a general loss in diversity was recorded at the sites analyzed, the frequencies of the occurrence of aphids in different biological and ecological groups remained the same (except at Wzgórze Zamkowe -site E).This indicates that there have not been similar changes in the habitats there and that it is possible to limit further losses if modern methods of protecting natural resources, which take into account the contemporary achievements of science, were used (Forman, 1995;Kunz, 2016).Therefore, one should consider actively protecting these sites, especially in respect to regaining and restoring ecological corridors.Perhaps, it will be necessary to limit tourism in order to avoid losing these precious dry calcareous grasslands (even the relic ones at Góra Brodło -site D: Wika, 1986).

Changes in landscape
Due to intensive human activity in a relatively small area, Europe has been and continues to experience a loss of biodiversity.This applies particularly to Central Eu-   rope.In this region, the character of the economy changed after changes in the political system.As a result, the direct actions that infl uence nature have intensifi ed.They are especially visible in the transformation of landscapes, especially by their fragmentation (e.g.new traffi c routes, housing, tourist accommodation, agrocenoses, bodies of water etc.).The fragmentation of habitats causes a significant loss of biodiversity (Krauss et al., 2010).This process is signifi cantly infl uenced by the size of the fragments in the habitats that are saved (if their surface area decreases, this process becomes more intense) or the loss of ecological corridors (no connection between local populations of a species within the metapopulation can lead to its extinction) (Burkey, 1989;Moilanen & Hanski, 1998;Collinge, 2000;Wallis De Vries et al., 2002).These phenomena are the main causes of the loss of biodiversity in the habitats studied.Although the sites that were analyzed in this study have been protected since the 1950s, due to changes in the political system and the introduction of a market economy, their surrounding area was heavily transformed, which broke the connections between protected patches and sites.

Biological and ecological groups
In addition, sheep farming, which was undoubtedly a stabilizing factor, was also abandoned (Fischer et al., 1996;Poschlod & Bonn, 1998).Moreover, the recent intensive development of tourism in these areas is not a factor that promotes the preservation of the status of these areas (Vaughan, 2000).

CONCLUSION
This analysis demonstrates there has been a considerable decrease in the biodiversity of aphids in the entire area studied over a period of a quarter of a century.This process is especially dangerous because it has resulted in the loss of ubiquitous species, which results in the gradual "homogenisation of communities", which along with a small increase in generalist species leads to the synanthropisation of communities.The main cause of these changes is human activity associated with the economy (development of agriculture and tourism).As a result, the connectivity among local habitat islands no longer exists due to the disappearance of ecological corridors.In addition, such isolated islands gradually become limited territorially (decreased), which reduces the level of connection among the local populations of species within metapopulations, which, along with the decrease in their area, affect the rate of extinction.If we combine these regional factors with global ones (climate change), then the processes of extinction become more dramatic.Obviously, the confl ict between "anthropogenization" and biodiversity (since the fi rst human settlements) will continue and its balance will never be equal to zero (as in the natural landscape).However, by applying the principles of sustainable development (taking into account the results of the latest ecological trends), the process can be or even should be mitigated.In the long term, it may turn out that the expected benefi ts from the infrastructure that is created will only be an insignifi cant percentage of the losses that are associated with the decrease in biodiversity.

Fig. 1 .
Fig. 1.Non-metric multi-dimensional scaling (NMDS) ordination of the results for all of the sites studied in two-dimensional space.Explanations: A-E -sites; 1 -historical data, 2 -current data.

Table 1 .
Previous and current occurrence of aphids at the sites studied, taking into account biological and ecological groups.† -lost species, * -new species.

Table 2 .
The percentage of biological and ecological groups of aphids at the sites studied. 1 -historical data, 2 -current data.Data in bold are signifi cant (G-test) at p < 0.05.