Urbanization, environmental stabilization and temporal persistence of bird species: a view from Latin America

BackgroundA scarcely studied consequence of urbanization is the effect of temporal stabilization of the environment on bird communities. This alteration is thought to dampen environmental variations between day and night, seasons and years, promoting a temporal persistence of bird composition in urban areas. The aim of this study was to review current evidence of temporal stabilization of biotic and abiotic factors in urban environments and the potential effects of such stabilization on temporal variation of bird species presence at different temporal scales.MethodsI selected the literature by searching published articles and book chapters using Scopus and Google scholar. I only included articles that compared the temporal variation of bird composition or resources between different levels of urbanization.ResultsIn general, there is evidence of temporal stabilization of abiotic and biotic factors at the three time scales considered. At the diurnal scale, the main factor considered was artificial light in the context of light pollution. At the seasonal and interannual scales, several case studies found a smaller temporal variation of primary productivity in urban than in natural and rural areas. Bird species composition showed more stabilization in urban environments at the three temporal scales: (1) several case studies reported bird activity at night, associated with artificial light; (2) studies in urban parks and along urbanization gradients showed smaller seasonal variation of bird composition in the more urbanized areas; and (3) in general, case studies along urbanization gradients showed smaller interannual variation of bird composition in the more urbanized areas, although some studies showed no relationships or opposite trends than expected.DiscussionThe published evidence suggests that urban areas dampen the natural cycles at several temporal scales. The stabilization of biotic and abiotic factors, such as light, temperature, food and habitat structure, is desynchronized from natural diurnal, seasonal and interannual cycles. However, there is a dearth of long-term comparisons of bird composition and studies that simultaneously analyze the relationship between resources and bird composition stabilization at the seasonal and interannual scales. More research is needed in the Southern hemisphere, where there is a lack of studies dealing with the seasonal and interannual variations of primary productivity along urbanization gradients and nocturnal activity of bird species. A future research agenda should include differentiation of spatial and temporal homogenization of avifaunas.

Urbanization, resources stabilization and the temporal persistence of bird species: A review

Background. A scarcely studied consequence of urbanization is the effect of the temporal stabilization of habitat structure and resources on bird communities. This alteration is thought to dampen environmental variations between day and night, seasons and years, promoting a temporal persistence of bird composition in urban environments. The aim of this study is to review actual evidence of temporal stabilization of habitats and resources in urban environments, and its potential effects on the temporal variation of bird species presence among different temporal scales. Methods. Selection of literature was made by searching published articles and book chapters using Google scholar. I only included articles that compared the temporal variation of bird composition or resources between different levels of urbanization. Results. In general, there is evidence of temporal stabilization of habitat structure and resources along the three scales considered. At the diurnal scale, the main factor considered was artificial light in the context of light pollution. At the seasonal and interannual scales, several case studies found a lesser temporal variation of primary productivity in urban areas compared with natural and rural areas. Bird species composition showed more stabilization in urban environments at the three temporal scales: 1) several case studies reported bird feeding at night, associated with artificial light; 2) studies in urban parks and along urbanization gradients showed lower seasonal variation of bird composition in the more urbanized areas; and 3) in general, case studies along urbanization gradients showed lower interannual variation of bird composition in the more urbanized areas, although some studies showed no relationships or opposed trends than expected. Discussion. The published evidence suggests that urban areas dampen the natural cycles at several temporal scales. The stabilization of biotic and abiotic factors, such as light, temperature, food and habitat structure are desynchronized from natural diurnal, seasonal and interannual cycles. However, there is a dearth of studies that simultaneously analyze the relationship between resources and bird composition stabilization. I also emphasize the need to differentiate spatial and temporal homogenization of avifaunas for a future research agenda. Moreover, the relationship between urbanization and other taxa is also commented. Finally, I propose suggestions for future work at different spatial scales.

Urbanization, resources stabilization and the temporal persistence of bird species: A review

Background. A scarcely studied consequence of urbanization is the effect of the temporal stabilization of habitat structure and resources on bird communities. This alteration is thought to dampen environmental variations between day and night, seasons and years, promoting a temporal persistence of bird composition in urban environments. The aim of this study is to review actual evidence of temporal stabilization of habitats and resources in urban environments, and its potential effects on the temporal variation of bird species presence among different temporal scales. Methods. Selection of literature was made by searching published articles and book chapters using Google scholar. I only included articles that compared the temporal variation of bird composition or resources between different levels of urbanization. Results. In general, there is evidence of temporal stabilization of habitat structure and resources along the three scales considered. At the diurnal scale, the main factor considered was artificial light in the context of light pollution. At the seasonal and interannual scales, several case studies found a lesser temporal variation of primary productivity in urban areas compared with natural and rural areas. Bird species composition showed more stabilization in urban environments at the three temporal scales: 1) several case studies reported bird feeding at night, associated with artificial light; 2) studies in urban parks and along urbanization gradients showed lower seasonal variation of bird composition in the more urbanized areas; and 3) in general, case studies along urbanization gradients showed lower interannual variation of bird composition in the more urbanized areas, although some studies showed no relationships or opposed trends than expected. Discussion. The published evidence suggests that urban areas dampen the natural cycles at several temporal scales. The stabilization of biotic and abiotic factors, such as light, temperature, food and habitat structure are desynchronized from natural diurnal, seasonal and interannual cycles. However, there is a dearth of studies that simultaneously analyze the relationship between resources and bird composition stabilization. I also emphasize the need to differentiate spatial and temporal homogenization of avifaunas for a future research agenda. Moreover, the relationship between urbanization and other taxa is also commented. Finally, I propose suggestions for future work at different spatial scales.

TRENDS OF HIDDEN EMPLOYMENT IN LITHUANIA AND PROBLEMS IN METHODICAL CALCULATIONS / NEOFICIALAUS UŽIMTUMO TENDENCIJOS LIETUVOJE IR METODINĖS SKAIČIAVIMŲ PROBLEMOS

The article discusses the extent of hidden employment in Lithuania and its dynamics tendencies, different methodologies used for the assessment of this phenomenon are reviewed and the problems this assessment faces are discussed. Because the estimation of hidden employment extent is very complicated and multiple problem the article is based on various data sources and on the methodology of statistical researches. The article widely presents the results of survey of Statistics Lithuania and it's acummulated experience, various methodological problems of hidden employment estimation are disscused. Employed in the unofficial labour market population dynamics tendencies are estimated based on prepared methodology of calculation by the Institute of Labour and Social Research scientists). According to calculations made by authors, hidden employment in Lithuania kept growing fast and reached the maximum value of 380 thousand till 1994. Later (in 1995–2001) it declined substantially to 230 thousand. 2002–2004 were the year of temporal stabilization (with a number of 210 thousand illegally employed), after which a period of sudden fall took place (down to 120 thousand in 2008). Despite this, the favorable conditions for hidden employment growth were formed in 2009, while in the threat of the economic crisis the country experienced an especially deep recession. Increased taxes and unemployment, made the favorable conditions for shadow business. Santrauka Straipsniu siekiama įvertinti neoficialaus užimtumo apimtį ir jo dinamikos tendencijas bei apžvelgti skirtingas šio reiškinio skaičiavimų metodikas. Kadangi neoficialaus užimtumo (nelegalaus darbo) apimties įvertinimas itin sudėtinga ir įvairialypė problema, analizuojant situaciją naudotasi įvairiais duomenų šaltiniais: skirtingų institucijų apklausų duomenimis, specialių skaičiavimų rezultatais. Straipsnyje plačiai naudojami Statistikos departamento prie Lietuvos Respublikos Vyriausybės (toliau – Statistikos departamento) atlikto tyrimo rezultatai ir sukaupta patirtis, aptariamos įvairios metodinės neoficialaus užimtumo įvertinimo problemos. Dirbančiųjų neoficialioje darbo rinkoje dinamikos tendencijos įvertinamos remiantis Darbo ir socialinių tyrimų instituto mokslininkų parengta skaičiavimo metodika, prie kurios kūrimo prisidėjo straipsnio autoriai. Be to, siekiant geriau ištirti nagrinėjamą problemą naudojamasi Darbo ir socialinių tyrimų instituto atlikto specialaus tyrimo (“Nelegalaus darbo, teisės aktų, reglamentuojančių darbo santykius, pažeidimų, darbdavių atstovų grasinimų ar kitokio psichologinio pobūdžio įtakos darbuotojų darbo rezultatams bei saugai ir sveikatai 2004–2005 m.“) rezultatais. Kaip parodė autorių skaičiavimai, iki 1994 m. neoficialusis užimtumas Lietuvoje augo itin sparčiai ir pasiekė maksimalią 380 tūkst. reikšmę, o 1995–2001 m. labai sumažėjo (iki 230 tūkst.). 2002–2004 m. buvo laikinas stabilizacijos laikotarpis (dirbančiųjų neoficialioje darbo rinkoje buvo 210 tūkst.), po kurio šis rodiklis sparčiai mažėjo (iki 120 tūkst. 2008 m.). Nepaisant to, palankios neoficialaus užimtumo augimo sąlygos susiformavo 2009 m., kai grėsmingos ekonominės krizės metu šalyje ypač stipriai pasireiškė ūkio nuosmukis, išaugus mokesčiams ir nedarbui tiesiog suklestėjo šešėlinis verslas. Būtina pabrėžti ir tai, kad įvairūs neoficialaus užimtumo apimties vertinimai stipriai skiriasi. Autorių skaičiavimais, kurių pagrindas yra “Sodros“ duomenys, neoficialaus užimtumo mastas 2003 m. siekė apie 200 tūkst. užimtųjų, o tų metų neapskaitomos ekonomikos tyrimo duomenimis, jis siekė apie 100 tūkst. Apibendrinant skirtingus duomenų šaltinius, galima pateikti nelegalaus darbo apimties (dirbančiųjų neoficialioje darbo rinkoje skaičiaus) tikėtinas svyravimo ribas. 2003 m. šis rodiklis galėjo svyruoti nuo 100 iki 200 tūkst. Viršutinė šio intervalo riba remiasi autorių atliktais skaičiavimais. Šiuos skirtumus galima aiškinti tiek apytikriu vertinimų pobūdžiu, tiek metodiniais skaičiavimų skirtumais. Deja, nėra galimybės palyginti naujesnių rodiklių, nes neapskaitomos ekonomikos tyrimas šalyje atliekamas maždaug kas 10 metų.