Structure and functioning of food webs in the

Structure and functioning of food webs in the fish communities of the Ohrid, Prespa and Skadar lakes – a qualitative modelling approach M. Pavlova 1 , D. Milosevic 2, A. Talevska 3, Lachezar Pehlivanov 1 and T. Talevski 4 1 Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences Sofia, Bulgaria. 2 University of Montenegro, Faculty of Science and Mathematics, Department of Biology, Podgorica, Montenegro. 3 University of Belgrade, Faculty of Biology, Belgrade, Republic of Serbia. 4 University “St. Kliment Ohridski”, PSI Hydrobiological Institute, Ohrid, Republic of Macedonia. E-mail: mnp. iber@gmail. com BALWOIS, Ohrid 2012 1

The tragedy of the commons. . A finite world can support only a finite population. . Hardin, 1968 Trophic Ecology A framework for proceeding in decision-making that aims to provide the best available evidence to decision-makers on the likely outcomes of alternative actions, WHICH IS OF HIGH IMPORTANCE FOR MANAGING THE DELICATE BALANCE OF THE LACUSTRINE ECISYSTEMS UNDER ANTHROPOGENIC PRESSURE AND IMPACT BALWOIS, Ohrid 2012 2

The study: MAIN TASK: To build the trophic webs, to define key species and to make predictions about further development of the ecosystem in different conditions. for Giving a simple get - at – able explanation of important processes in the reservoirs ecosystem. BALWOIS, Ohrid 2012 3

The consistency: Species composition of the ichthyocenoses in the three lakes Defining the trophic groups. The trophic affiliation of the fish species and the trophic index - referred to recent data, presented in the e-source Fish. Base. org with the cited references. The similarity checking among the trophic structure of the fish communities in the three lakes - “PRIMER v 6” software The models of trophic webs in the three compared fish communities - built using Power. Play software for Loop analysis, designed in the Oregon State University, USA. BALWOIS, Ohrid 2012 4

Six trophic groups were identified among the focused fish species (Table 1) according the predominating food component as follows: -Piscivores, i. e. predaceous fishes; -Phytoplanktivores (feeding mainly on planktonic algae); -Macrophytivores (feeding maily on submerged high plants); -Zoobentivores feeding mainly on macrozoobenthos); -Zooplanktivores (feeding mainly on zooplankton); -Omnivores (feeding on more than one trophic level (for example, Ohrid bleak Alburnus belvica which main food consists equally from phyto- and zooplancton). BALWOIS, Ohrid 2012 5

Significant similarity of the species composition in the trophic groups of Zooplanctonivores, Phytoplanctonivores and Macrophytivores was also found. Diferent composition of the trophic groups of omnivorous, macrozoobenthivorous and predaceous fish was reported in each lake. BALWOIS, Ohrid 2012 6

The trophic index OHRID LAKE PRESPA LAKE SKADAR LAKE BALWOIS, Ohrid 2012 7

Qualitative community matrix models- LOOP analysis • SIMPLE modeling for NON- MATEMATICIANS, based only on matrices; • Helps to define system and focus research; • Gives general predictions about changes in the model when the system is “pressed”; • An analysis of the “reliability” of those predictions is available • …….

Qualitative models (loop analysis): A : Variables : Positive relationship : Negative self- effect : Positive self- effect BALWOIS, Ohrid 2012 9

THE MODDELED FOOD WEBS OHRID and SKADAR LAKES The Ohrid and the Skadar Lake trophic web general- (a) and prediction with increasing the level of significance of Macrozoobenthos factor (b) Legend: Zpl- zooplankton; Phpl- phytoplankton; DOM- dissolved organic matter; Mphy- macrophytes; hxv- sun light; Mzb- macrozoobenthos, Phb- phytobenthos, Zplv. F- zooplanctivorous fish; Mzbv. F- macrozoobenthivorous fish; Omni. F- omnivorous fish; Pr. F- predaceous fish; the red circles means dincreasing of the level of significance of the relative factor and the yellow ones- decreasing of it BALWOIS, Ohrid 2012 10

PRESPA LAKE The Prespa. Lake trophic web general- (a), prediction with decreasing the level of significance of macrophytivorous fish trophic group factor (b) and simplified trophic relation among the omnivorous Ohrid bleak and the native and non-native- salmonid species. Legend: Zoopl- zooplankton; Phpl- phytoplankton; DOM- dissolved organic matter; Mphy- macrophytes; hxv- sun light; Mzb- macrozoobenthos, Phb- phytobenthos, Zplv. F- zooplanctivorous fish; Mzbv. F- macrozoobenthivorous fish; Omni. F- omnivorous fish; Pr. F- predaceous fish; Abelv- A. belvica; Sper- S. peristericus; Omyk- O. mykkis; the red circles means increasing of the level of significance of the relative factor and the yellow ones- decreasing of it. BALWOIS, Ohrid 2012 11

Conclusions The functioning of the presented trophic webs is influenced of the trophic state of the three studied lakes. The oligotrophic Ohrid Lake fish community functioning differs significant from these in the meso- and eutrophic Skadar and Prespa Lake The trophic web in the deep oligotrophic Ohrid Lake with poorly developed vegetation might be regarded as a primary stage in the evolution of trophic relationships in the lacustrine ecosystem. At the opposite end is the shallow eutrophic Prespa Lake overgrown with macrophytes. The Skadar Lake occupies intermediate position with two clearly separated zones – a large shallow area overgrown with macrophytes and a deep zone with less developed vegetation. The habitat diversity there is a prerequisite for development of both the types of the trophic webs. BALWOIS, Ohrid 2012 12

An advantage of keeping the things simple: …”Shifting baseline syndrome (SBS) is a cautionary tale referring to changing human perceptions of biological systems due to loss of experience about past conditions. ” Papworth et all. , 2009 THANKS! Questions? BALWOIS, Ohrid 2012 13