Lectura 1, Apuntes de Biología

¡Descarga Lectura 1 y más Apuntes en PDF de Biología solo en Docsity! a c t a o e c o l o g i c a 3 4 ( 2 0 0 8 ) 3 0 3 – 3 1 0ava i lab le at www.sc ienced i rec t . com journa l homepage : www. e lsev ier . com/ loca te /ac toecOriginal article Human population, grasshopper and plant species richness in European countriesClaude E. Stecka,1, Marco Pautassob,* aSection of Nature Conservation and Historical Ecology, Department of Landscape, Federal Research Institute WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland bDivision of Biology, Imperial College London, Silwood Campus, Buckhurst Road, Ascot SL5 7PY, UKa r t i c l e i n f o Article history: Received 18 March 2008 Accepted 9 June 2008 Published online 25 July 2008 Keywords: Biogeography Entomology Human beings Latitudinal gradient Macroecology Spatial autocorrelation Species–area relationship Taxa co-occurrence* Corresponding author. Tel.: þ44 020 759 42 E-mail address: m.pautasso@ic.ac.uk (M. 1 Present address: Planungsbüro Brinkman 1146-609X/$ – see front matter ª 2008 Elsev doi:10.1016/j.actao.2008.06.003a b s t r a c t Surprisingly, several studies over large scales have reported a positive spatial correlation of people and biodiversity. This pattern has important implications for conservation and has been documented for well studied taxa such as plants, amphibians, reptiles, birds and mammals. However, it is unknown whether the pattern applies also to invertebrates other than butterflies and more work is needed to establish whether the species–people relation- ship is explained by both variables correlating with other environmental factors. We stud- ied whether grasshopper species richness (Orthoptera, suborder Caelifera) is related to human population size in European countries. As expected, the number of Caelifera species increases significantly with increasing human population size. But this is not the case when controlling for country area, latitude and number of plant species. Variations in Caelifera species richness are primarily associated with variations in plant species rich- ness. Caelifera species richness also increases with decreasing mean annual precipitation, Gross Domestic Product per capita (used as an indicator for economic development) and net fertility rate of the human population. Our analysis confirms the hypothesis that the broad-scale human population–biodiversity correlations can be explained by concurrent variations in factors other than human population size such as plant species richness, en- vironmental productivity, or habitat heterogeneity. Nonetheless, more populated countries in Europe still have more Caelifera species than less populated countries and this poses a particular challenge for conservation. ª 2008 Elsevier Masson SAS. All rights reserved.1. Introduction 2003; Willig et al., 2003). Together with ecosystem composi-The increased availability of geo-referenced data on the occur- rence of a wide range of species has made possible a rapidly increasing amount of investigations on large-scale patterns of biodiversity (e.g. Purvis and Hector, 2000; Hawkins et al.,533. Pautasso). n, Holunderweg 2, 79194 ier Masson SAS. All rightstion, structure, and function, one of the central aspects of biodiversity is species richness (Noss, 1990). Species richness is often positively correlated with the number of habitat types and with higher levels of ecosystem function, services and health (e.g. Böhning-Gaese, 1997; Simberloff, 1999; Naeem,Gundelfingen, Germany. reserved. a c t a o e c o l o g i c a 3 4 ( 2 0 0 8 ) 3 0 3 – 3 1 03042002; Egoh et al., 2007). Surprisingly, recent studies have shown that species richness can be positively correlated also with human population size (e.g. Luck, 2007a). Typically, a positive species–people correlation has been documented over large regions, both in terms of study grain and extent. These reports have come from Africa (e.g. Balmford et al., 2001; Burgess et al., 2007), North (e.g. McKinney, 2001; Vazquez and Gaston, 2006) and South Amer- ica (e.g. Diniz et al., 2006; Fjeldså, 2007), Asia (e.g. Ding et al., 2006), Australia (Luck et al., 2004; Luck, 2007b), and Europe (e.g. Araújo, 2003; Moreno-Rueda and Pizarro, 2007). A large- scale positive species–people correlation has important consequences for conservation, as the negative local impact of human beings on biodiversity will be even stronger if, over large scales, species-rich regions tend to be more densely inhabited. In these studies, plants, butterflies, amphibians, reptiles, birds and mammals have been analyzed (e.g. Gaston, 2005). The obvious reason for this taxonomic choice is the relatively large availability of data for these groups (e.g. Gaston and May, 1992; Fazey et al., 2005a; Lonsdale et al., 2008). As a conse- quence, it is still largely unknown whether invertebrates other than butterflies also tend to have higher species richness where there is higher human population. Many invertebrate species might respond to the presence of human beings in a different way than plants and vertebrates given their differ- ent body sizes, life histories and space use. Moreover, the large-scale human population–biodiversity correlation observed might be the consequence of both vari- ables correlating with other environmental factors. Both spe- cies and human beings tend to thrive in regions of higher environmental productivity (e.g. Chown et al., 2003; Vazquez and Gaston, 2006; Novotny et al., 2006; Fjeldså, 2007). It has been thus hypothesized that when controlling for confound- ing factors such as habitat heterogeneity and environmental productivity the species–people correlation might be absent. Therefore, there is a need for further studies of this issue con- trolling for factors potentially co-varying with species rich- ness and human presence. In this study, we test whether or not there is a positive human population–species richness correlation in European countries for grasshoppers (Orthoptera, suborder Caelifera) controlling for variations in area, latitude, plant species rich- ness, and for spatial autocorrelation. Grasshoppers (Caelifera) are an important group of herbivorous insects. They are leaf chewers during all their life stages and are not restricted to a particular biogeographical region. Grasshoppers are not only characterized by widespread distribution, high diversity and functional importance, but also by sensitivity to distur- bance. All these features make them useful indicators for hab- itat degradation and for ecosystem management (e.g. Illich and Haslett, 1994; Baldi and Kisbenedek, 1997; Andersen et al., 2001; Bock et al., 2006; Davidson and Lightfoot, 2007). Grasshoppers have already been the object of biogeographical analysis (e.g. Otte, 1976; Davidowitz and Rosenzweig, 1998; Cigliano et al., 2000; Gavlas et al., 2007), but to the best of our knowledge they have not been included in studies of the species–people relationship. Europe is a suitable area for analyzing the coexistence between species and people, as it is a region of relativelyhigh population. As a rule, European countries have a lower presence of species relative to other continents due to (i) their usually small size, (ii) their distance from the tropics and (ii) the mountain ranges of the Alps and Pyrenees parallel to the equator which posed a barrier to species migration during the repeated glaciation events (Hewitt, 1996). Nevertheless, Europe hosts regions of high plant biodiversity (e.g. the Mediterranean hotspot; e.g. Medail and Quezel, 1999; Myers et al., 2000). Moreover, the spatial distribution of species occurrences is relatively well investigated in Europe, given the high number of taxonomists and the long tradition of research on biodiversity (e.g. Gaston and May, 1992; France et al., 1998; Fazey et al., 2005b). Although administrative areas are not ideal in macroecological analyses due to the arbitrary boundaries, European countries have been successfully used as sample units in biogeographical studies of bird abundance and butterfly species richness in relation to socio-economic factors (Gaston and Evans, 2004; Konvicka et al., 2006). However, pan-European biogeographical studies have been rare, possibly because of the political and linguistic fragmen- tation of the different countries.2. Methods Estimates of species richness for the suborder Caelifera (Orthoptera) of European countries were obtained from the Fauna Europaea database (Fauna Europaea, 2004). This data set is the product of a collaborative project of the European Union. It was coordinated, generated and validated by, respec- tively, the Zoological Museum of Amsterdam (Netherlands), the Zoological Museum of Copenhagen (Denmark) and the National Museum of Natural History of Paris (France). Overall, the project involved more than 400 taxonomic experts (Fontaine et al., 2007). Human population size (referring as a rule to 2002), area and geographical coordinates of the European countries/ regions were retrieved from EUROSTAT (ec.europa.eu/ eurostat). Estimates of plant species richness were usually obtained from Gleich et al. (2000). Plant species richness was used as an indicator for habitat diversity. Given that a reason- able estimate of grasshopper species richness was available for Corsica, Sardinia and Sicily, these islands were analyzed separately from mainland France and Italy. However, data from groups of islands such as the Azores, Balearic, Canary, Channel, Dodecanese, Faroe and Svalbard Islands were excluded from analyses, as in these cases the isolation of different islands might have increased the number of species observed due to speciation events. Given the unreasonably low estimate of grasshopper species richness (zero or a few species) for Gibraltar, Iceland, Monaco, Northern Ireland, San Marino, and Vatican City, these countries were excluded from analyses. Russia was not included in analyses as only an estimate for grasshopper species richness in five parts of Russia and not for the whole of it was available. Overall, 42 countries/regions were retained in the data set analyzed (Table 1). The range, mean, median and standard deviation of the response and explanatory variables are given in Table 2. The correlation of Caelifera species richness with human population size was analyzed on its own and controlling for r2 = 0.14, y = 0.31 + 0.22 x, s.s.e. = 0.03, p < 0.0001 0.0 1.0 2.0 3.0 2.0 3.0 4.0 5.0 6.0 log10 country area lo g 1 0 gr as sh op pe r sp p ri ch ne ss Fig. 3 – The relationship between grasshopper species richness and area (km2) in 42 European countries on a log– log scale (s.s.e. [ slope standard error). a c t a o e c o l o g i c a 3 4 ( 2 0 0 8 ) 3 0 3 – 3 1 0 307human population size with latitude (n¼ 42, r2¼ 0.04, log pop¼ 5.84þ 0.018 lat, s.s.e.¼ 0.016, p¼ 0.25).  there was a significant increase of country area with increasing latitude (n¼ 42, r2¼ 0.15, log area¼ 2.69þ 0.04 lat, s.s.e.¼ 0.02, p¼ 0.01).  there was a significant decrease in mean annual precipita- tion with increasing mean annual temperature, but the variance explained was negligible (n¼ 42, r2¼ 0.01, log prec¼ 2.99 0.23 log temp, s.s.e.¼ 0.09, p¼ 0.01).  there were no significant variations of net fertility rate with variations in GDP (n¼ 42, r2¼ 0.01, nfr¼ 2.64 0.24 log GDP, s.s.e.¼ 0.17, p¼ 0.17).4. Discussion As reported for other taxa analyzed in many recent regional studies (see Section 1), the number of Caelifera species in European countries increases with increasing human popula- tion size. One fifth of the variance in Caelifera speciesr2 = 0.25, y = 2.43 - 0.02 x, s.s.e. = 0.01, p = 0.05 0.0 1.0 2.0 3.0 30 40 50 60 70 latitude N lo g 1 0 gr as sh op pe r sp p ri ch ne ss Fig. 4 – The relationship between log-transformed grasshopper species richness and latitude in 42 European countries (s.s.e. [ slope standard error).numbers is explained by variations in human population size. Nonetheless, when controlling for plant species richness, country area and latitude, there is no longer a significant increase of Caelifera species richness with increasing human population size. As documented for other insect groups (e.g. Gaston, 1992; Hawkins and Porter, 2003; Lewinsohn et al., 2005), over regional scales grasshopper species richness is mainly associated with plant species richness. This implies that recently reported positive large-scale species–people relationships may be an artefact of both species richness and human population size being positively associated with other factors, in this case plant species rich- ness. There is some independent evidence that this may be the case for other taxa and regions, for example for birds in East Asia, where the positive relationship between species richness and human population turns into a negative one when controlling for environmental productivity (Ding et al., 2006). Another explanation of the observed positive species–peo- ple relationships could be that, over large scales, higher human population size is concomitant with higher diversity of habitats, which in turn correlates with higher species rich- ness (e.g. Kühn et al., 2004; Luck, 2007a; Pautasso, 2007). Plant species richness can be expected to be positively correlated with the diversity of habitat types (although only a subset of plant species will be of relevance for grasshoppers, as these are mainly present in open habitats such as grasslands). As European countries with higher Caelifera species richness also have a higher number of plant species, this analysis pro- vides evidence for a role of habitat heterogeneity in explaining positive large-scale species–people relationships. Even if a dif- ferent result may be obtained at a more local scale or with a lower number of plots (e.g. Niemelä and Baur, 1998), our findings make it even more important to conserve plant spe- cies richness as well as habitat heterogeneity in European countries. It is also possible that in some cases species richness may positively correlate with human population size due to a more thorough knowledge of species occurrences in more populated countries (for grasshoppers, see Davidowitz and Rosenzweig, 1998). However, this bias is not likely as the estimates of grasshopper species richness used in this study were obtained from a database which was compiled and vali- dated by the leading taxonomists in the European Union (Fontaine et al., 2007). Additionally, provided that plant species richness itself does not suffer from sampling bias, sampling bias does not need to be invoked as explanation for a positive species–people relationship for Caelifera in Euro- pean countries, as controlling for plant species richness makes this relationship disappear. Additionally, there is some independent evidence that at least for birds and plants such a sampling argument may not explain the observed positive species–people relationships (Evans et al., 2007; Pautasso and McKinney, 2007). Interestingly, there is no significant association of country area with Caelifera species richness when controlling for plant species richness, human population, and latitude. A positive species–area relationship is a very general pattern in ecology (e.g. Lawton, 1999), and has been confirmed for var- ious groups of insects (e.g. Connor and McCoy, 1979; Drakare a c t a o e c o l o g i c a 3 4 ( 2 0 0 8 ) 3 0 3 – 3 1 0308et al., 2006; Finlay et al., 2006; Maraun et al., 2007). However, species richness might not correlate with area per se. In many cases, species richness might increase with area only because of a third correlating factor, e.g. habitat heterogeneity (e.g. Storch et al., 2003; Hoyle, 2004; Krauss et al., 2004). The results presented here also show a negative, linear latitudinal gradient of Caelifera species richness, as usually found in most ecosystems (e.g. Hawkins et al., 2003; Willig et al., 2003). For grasshoppers, such a latitudinal gradient is known from North America, where increasing spatial hetero- geneity towards the tropics has been shown to be a mecha- nism behind the observed unimodal gradient (Davidowitz and Rosenzweig, 1998). That study is consistent with our finding that Caelifera species richness increases with plant species richness, given that the latter increases with decreas- ing latitude. However, there is some variance in Caelifera species amongst European countries which is not explained by variations in plant species richness and may be related to other factors. Main drivers of grasshopper species richness can encompass climate, mid-domain effects and topographi- cal heterogeneity (e.g. Gebeyehu and Samways, 2006; Steck et al., 2007a). Our analysis shows that there is a significant role of precipitation but not of temperature in explaining the variability of Caelifera species richness amongst European countries, with an increase of species with decreasing mean annual precipitation. Grasshoppers are typically associated with open habitats, and the presence of tree-less habitats is favoured by a dry climate. As for the socio-economic factors analyzed, there is evi- dence that countries with a lower GDP have a higher species richness of Caelifera. It might be thought that level of economic development mirrors the gradient in precipitation from west to east, but for the countries analyzed there is no significant association of GDP with mean annual precipitation (unpublished observations). It is likely that less developed countries may still have large areas of extensive pasture and grasslands, which are more suitable habitats for grasshoppers than areas with intensive agriculture. Moreover, there is a neg- ative association of Caelifera species richness with the current net fertility rate of European countries. Countries with higher current human fertility have a lower presence of Caelifera species richness. Provided that human migration will not make predictions on future demography based on the current net fertility rate meaningless, this finding implies that future human population decline will tend to occur in regions of higher European grasshopper biodiversity. Nevertheless, a large-scale positive correlation between species and people implies that the local negative anthropogenic impacts will be worse than if over large scales the presence of species and people were negatively correlated. The finding that coun- tries with fewer species also have fewer human beings than species-rich countries poses thus a concrete conservation challenge.5. Conclusions Although variations in Caelifera species richness amongst European countries are largely associated with variations in plant species richness, more populated European countriesdo have a higher number of Caelifera species than less popu- lated ones. Therefore, most European people live in countries with a high biodiversity, both in terms of plants and grasshop- pers. This is a positive finding as it provides an opportunity to experience relatively high levels of biodiversity to the majority of the European population. However, the spatial co-occur- rence of high numbers of species and of human beings is a challenge for conservation. This is because detrimental effects of urbanization and other human activities can cause biodiversity homogenization (e.g. Kühn and Klotz, 2006; La Sorte and McKinney, 2006), although more research is needed to assess whether this is the case also for less studied taxa such as grasshoppers. Our analysis shows that there is substantial variation in Caelifera species richness amongst European countries, and that this variation is well correlated with plant species richness. Given that the regional pool of species can be an important determinant of the success of grasshopper restora- tion measures (Knop et al., 2008), it is important that also large-scale grasshopper biodiversity be preserved. Traditional extensive agricultural activities may have benefited both plant and grasshopper biodiversity (e.g. Batary et al., 2007; Marini et al., 2008), but today’s intensification of land use, together with habitat fragmentation and the increasing abandonment of marginal land (e.g. Kruess and Tscharntke, 2002; Torrusio et al., 2002; Steck et al., 2007b; Öckinger and Smith, 2008), are major impediments for the achievement of the goal of halting biodiversity loss in Europe by 2010.Acknowledgments Many thanks to the many people involved in the compilation of the Fauna Europaea database, to H. Kreft for help in retriev- ing climate data, to A. Ambrosino, I. Currado, K. Evans, P. Ferrazzi, K. Gaston, O. Holdenrieder, S. Jackson, M. Jeger, M. McKinney, G. Powell, A. Rodrigues, L. Vazquez, P. Warren, P. Weisberg for insights and discussions, and to S. 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