Effects of temperature patterns on the spawining phenology and niche overlap of fish assemblages in the water bodies of the Dnipro River basin

The effect of the temperature on the spawining phenology of the fish assemblages and the role of the exogenious and
endogenious factors in temporal niche overlaping of fish assemblages were investigated in different water body types of the Dnipro River basin within the “Dnipro-Orilskiy" Nature Reserve (Ukraine in the years 1997-2018. The period of spawning (beginning and end) of the Blicca bjoerkna, Carassius gibelio, Scardinius erythrophthalmus, Abramis brama,Perca fluviatilis, Rutilus rutilus, and Esox lucius was estimated. Community niche overlap was estimated by calculating
the pairwise Pianka index. The temperature was discused as an exogenous factor effecting on the fishes spawn timing.
From 1998 to 2018 the average temperature in the study area continued to rise. The annual course of the temperature
takes the sinusoidal waveform, which can be described by a fourth-degree polynomial. The residuals of the
corresponding polynomial trend are specific for each year. The regular components of the residuals variation were
revealed by dbMEM-variables. Fishes spawning occurred within the narrow water temperature ranges, which are
specific for each fish species. There are statistically significant differences between ponds in water temperatures at
which the spawning start occurred. The water temperature at which the spawning start occurred is linearly dependent on
the time of the spawning start. There were temporal overlaps between spawning of the different species. The deviation
of the Pianka mean niche overlap indexes from random alternatives does not depend on the habitat type. The decreasing
trend of the Pianka mean niche overlap indexes was observed during the study period. There is no statistically
significant correlation between the average annual air temperature and the level of the niche overlap. The degree of
niche overlapping depends on broad-, medium-, and fine-scale temperature patterns.