Circadian rhythms of ground living spiders: mechanisms of coexistence strategy based on the body size

Circadian rhythms of activity are one of the many cases of the multidimensional mechanisms of species coexistence. Except of others, the mechanisms of coexistence strategy of spiders involve habitat, seasonal occurrence, food offers and body size of spiders. Circadian rhythm of activity of ground living spiders in floodplain forest and clearcut along the Morava River in the Litovelské Pomoraví Protected Landscape Area (Czech Republic, Central Europe) was studied. Activity of whole community was asymmetrical, diurnal activity was more frequent than nocturnal. Abundant species were analysed closely. Patterns of similarity in syntopic spider groups suggested the body size is significant factor influencing their circadian activity. We found out the predominantly small species achieved bimodal pattern of activity, influenced by the different activity of males and females. Generally we can conclude that spiders smaller than 5 mm were active during late night-morning and spiders bigger than 5 mm were active during afternoon and evening. This pattern was associated with changes of temperature of soil surface – big spiders were active during warmer parts of day. The presented data provide evidence of body-size differences among the spiders enable their coexistence in assemblages.