Distribution, abundance and species richness of butterflies and myrmecophilous beetles

Abstract

Suppealla alueella esiintyvät päiväperhoslajit ovat usein paikallisesti suhteellisen runsaslukuisia. Tämän yllättävän seikan havaitsi filosofian maisteri Jussi Päivinen tutkiessaan väitöskirjaansa varten päiväperhosia. Havainto on maailmanlaajuisesti erittäin harvinainen. Yhtenä syynä voi olla Suomen pohjoinen sijainti, jonka seurauksena monien päiväperhoslajien levinneisyysalue rajoittuu Etelä-Suomeen. - Levinneisyysalueensa reunalla elävät perhoslajit pystyvät asuttamaan ainoastaan suurimmat ja laadultaan parhaimmat elinympäristölaikut, mutta koska laikut ovat korkealaatuisia, niihin voi muodostua erittäin runsaslukuiset päiväperhoskannat. Reuna-alueella elävien päiväperhosten ns. elinympäristölaikut ovat todennäköisesti eristyneempiä kuin niiden lajien, joiden levinneisyysalue kattaa suuren osan tutkittavasta alueesta, Päivinen selvittää.

Several mechanisms have been proposed to explain the patterns of species richness, distribution and abundance. Also several mechanisms have been put forward in explaining the generally observed positive relationship between regional distribution and local abundance of species. In this thesis factors affecting distribution, abundance and species richness were studied using butterflies and myrmecophilous beetles as study objects. The data of myrmecophilous beetles are based on the literature and a field survey and data of butterflies is based on the literature. This thesis suggests that ant colonies maintain species rich beetle fauna, and that widespread host ant species and the species with large colony size are able to maintain higher species richness of myrmecophilous beetles. Surprisingly, a strong negative relationship between local abundance and regional distribution was found for the Finnish butterflies. The study suggested that sedentary butterfly species, species at the edge of their distribution range and the most specialized species were locally abundant with restricted distribution. Mobile species, species furthest from the edge of their distribution and generalist butterfly species were locally few in number and widespread, thus, generating the negative relationship. Larval specificity, habitat breadth and resource availability were observed to be in a key role when explaining the mobility of the butterflies. Range position had strong effect both on the mobility and on the length of the flight period of the butterflies. The surprising results emphasize the importance of the study of basic ecology of species. More studies are needed to find out, whether observed negative relationship between distribution and abundance is a more general phenomenon than previously thought.