The birds of Pasvik / E. I. Khlebosolov, O. A. Makarova, O. A. Khlebosolova [et al. ; English transl. Nikita Chernetsov]. - Ryazan : Golosgubernii, 2007. - 175 с. : ил., портр.

5 . У. Mullari The Pasvik Valley includes various landscapes, ranging from riparian forest to mountain tundra. When productivity o f habitats changes, it is not only the num b e r o f species that may change, but often the array o f species may change completely, as the pattern o f resource sharing is altered and thus the pattern o f b ioceno tic links w ithin the given ecosystem is completely revised (Khlebosolov & Khlebosolova 2005). Another im portant factor that contributes to low specific diversity o f Pasvik birds is the instability o f the environm ent. In the no rth the seasonal variation o f tem perature, humidity, and light conditions is very p ronoun c ed . This prevents birds from becom ing narrow foraging specialists. T herefore, the num b e r o f potential e co ­ logical niches and thus specific diversity o f birds in the n o rth is significantly reduced. Even though in some seasons productivity o f comm un ities may be com ­ paratively high, resource sharing and niche segregation occurs in a m ann er that allows the birds to survive under the most unfavourable co n d itio n s during the peri­ od o f m inimum productivity o f habitats (Southern 1970; Spray 1978; cited after Patterson 1980). 70