İstilacı Bir Balık Türü Gambusia holbrooki İle Endemik Bir Balık Türü Aphanius transgrediens'in Acıgöl (Denizli-Afyon) Kaynaklarındaki Yaşam Döngüleri, Besin Rekabeti ve Habitat Kullanımları

Abstract

Introduction of invasive species is currently considered as one of the main threats for biodiversity and ecosystem function. Gambusia holbrooki (mosquitofish), which has been introduced to many countries since the beginning of the 20th century in order to control mosquitoes, has now invaded all of the continents except Antarctica. Many studies have shown that G. holbrooki, known to threaten many native vertebrate and invertebrate groups, is the most important factor particularly in Europe, by threatening endemic Aphanius species. Turkey with its 13 endemic species of Aphanius, can simply be considered the center of speciation of this genus. Despite this, the biological and ecological characteristics of these species and the information on the impact of G. holbrooki on these species are quite insufficient. Within the scope of this thesis, sex ratios, age structures, growth, reproduction and feeding properties, food competitions and habitat use of critically endangered A. transgrediens, distributed in only Acıgöl (Denizli-Afyon) in the world, and the invasive G. holbrooki, which shares the same habitat, were addressed. iv Preliminary studies were carried out between March 2013 and September 2013 for the purpose of determining the population sizes and overall distributions of the species and habitat characteristics of the area. Following this, a total of 3 stations were selected, in which the interaction of two species was low and high, and the environmental conditions such as salinity and temperature were variable and constant, and monthly fish sampling was carried out accordingly between September 2013 and September 2014. It was determined that while G. holbrooki was present in all of the springs, A. transgrediens was inhabiting only in a few one with a limited population size. Female dominated sex structure is revealed in both species. While a lifespan of 2 years was presented in A. transgrediens, a maximum lifespan of 2 years for females and a maximum of 1 year for males was presented in G. holbrooki. It was found that the average length, length-at first maturity and absolute fecundity of both species were higher in variable environment, but G. holbrooki has a lower reproductive success than in the other stations. In addition, A. transgrediens and G. holbrooki were revealed to reproduce between February-May and AprilSeptember, respectively. It was determined that G. holbrooki fed mainly on Insecta (especially Diptera) adult and larvae as well as zooplankton and occasionally on vegetative sources. A. transgrediens was predominantly fed on detritus and filamentous algae in addition to Insecta larvae and zooplankton. Considering the feeding interactions, G. holbrooki was estimated to have a higher diet diversity and broader niche than A. transgrediens in the area, and put at a low rate of competition, predation and aggression pressure on A. transgrediens which resulted in a current and potential threat. However, it has been shown that the dietary composition of both species differed markedly in all stations studied and that A. transgrediens had herbivorous feeding strategy in the station with particularly variable conditions. It has been figured out that A. transgrediens can survive in large springs where there is a chance of using different parts of the habitat and in high sodium sulphate salinity due to their high tolerance, however G. holbrooki is affected negatively from high salinity. Therefore, it has been revealed that habitat shrinkage is one of the most important factors that may cause G. holbrooki to increase the adverse effect on A. transgrediens.