The spiders (Arachnida, Aranei) in the landscape reserve "Yakhnivsky" (Kyiv region)

For the first time, the species composition and relative abundance of spiders in pine and alder forests within the Yakhnovsky reserve have been studied; 46 species of spiders which represent 17 families were found. It was found that quantitatively in the pine forest spiders of the families Linyphiidae (43,4 %) and Araneidae (42,9 %) prevail, and in the alder forest – Tetragnathidae (37 %) and Linyphiidae (34 %). In the herbaceous layer of the pine forest, spiders of Araneidae family dominated quantitatively, and in the litter dominated Linyphiidae spiders – 91 %. In the herbaceous layer of the alder forest Tetragnathidae spiders quantitatively dominated – 34 %, and in the litter layer Linyphiidae and Tetragnathidae, are dominants – respectively, 32 % and 43 %. The dominant species for the grass and litter layers were revealed (according to the Tischler scale): in the pine forest, these are Mangora acalypha (48,6 %), Linyphia triangularis (18,85 %) and Leptothrix hardyi (89 %); in the alder forest – Linyphia triangularis (24,1 %), Metellina segmentata (23 %), Tetragnatha pinicola (18,8 %) and Piratula hygrophila (38,5 %) with Pachygnatha listeri (19,2 %), in accordance with indicated tiers. Nine species of spiders were identified, of which five species – Agroeca cuprea (family Liocranidae), Bathyphantes nigrinus, Dicymbium nigrum, Floronia bucculenta and Neriene montana (family Linyphiidae), are indicated for the first time for the territory of Kiev Polesie, and four species, for the first time for Ukrainian Polesie: Cheiracanthuim elegans (family Cheiracanthiidae), Leptothrix hardyi, Sintula spiniger and Walckenaeria alticeps (family Linyphiidae). For these species is given the data on faunal material, places and methods of collection, distribution and ecological features. According to our own research and literary sources, the territory of Kiev Polesie currently includes 150 species of spiders. The indices of faunistic similarity and species diversity of the surveyed biotopes were calculated, an arealogical analysis was performed.

Effect of phenology on agonistic competitive interactions between invasive and native sheet-web spiders

The phenologies of introduced relative to native species can greatly influence the degree and symmetry of competition between them. The European spider Linyphia triangularis (Clerck, 1757) (Linyphiidae) reaches very high densities in coastal Maine (USA). Previous studies suggest that L. triangularis negatively affects native linyphiid species, with competition for webs as one mechanism. We documented phenological differences between L. triangularis and three native species that illustrate the potential for the reversal of size-based competitive advantage over the course of the year. To test whether relative size influences interaction outcome, we allowed a resident spider to build a web and then introduced an intruder. We examined whether the outcomes of agonistic interactions over the webs were influenced by the species of the resident (invasive or native), the relative size of the contestants, and the species × size interaction. We found that the importance of relative size differed among species. In interactions between L. triangularis and each of two native species, size played a greater role than resident species on the outcome of interactions, suggesting that competitive advantage reverses over the season based on phenology-related size differences. Linyphia triangularis had a negative impact on the third species regardless of relative size.

A 4-year study of invasive and native spider populations in Maine

Invasive spiders pose potential threats to native spiders. In 2002, the European spider Linyphia triangularis (Clerck, 1757) (Araneae: Linyphiidae) was discovered in all but one county in Maine. At Acadia National Park, we conducted a 4-year study of L. triangularis and three native linyphiid species of a similar size ( Frontinella communis (Hentz, 1850), Pityohyphantes subarcticus Chamberlin and Ivie, 1943, and Neriene radiata (Walckenaer, 1842)). Using line-transect surveys, we measured population densities in coastal and forest habitat. The density of L. triangularis varied across years but was always significantly higher on the coast than in the forest. In contrast, only one native species was present on the coast and at very low numbers. Coastal L. triangularis were larger and in better condition than those in the forest, and numbers and biomass of insect prey were also higher on the coast. In 2 years, we also conducted transects at a second coastal location in Maine where the invader was at low density. At that site, native densities were substantially higher than at either Acadia site. Our data are consistent with the hypothesis that L. triangularis is reducing populations of native spiders. Companion studies suggest that L. triangularis negatively impacts natives by usurping both web sites and webs.