Araneae download the new version2/25/2024 ![]() Aquatic systems are rich in energetically valuable substrates (e.g., periphyton 6) and consequently emerging aquatic insects show high levels of essential highly polyunsaturated fatty acids (HUFA 7). The significance of aquatic insects in the terrestrial food web owes itself not only to the quantity (i.e., multiple mg C m −2 yr −1 for average-sized lakes 5), but also to the high nutritional quality that aquatic resources provide compared to terrestrial prey 4. An important link between aquatic and terrestrial systems is the nutritional subsidy of terrestrial habitats via the emergence of aquatic insects, though the reciprocal energy flow, namely terrestrial-to-aquatic (e.g., in form of nutrients and organic matter 3), is of comparable importance 4. Riparian zones are interfaces that link aquatic and terrestrial systems, and because of their habitat complexity, are characterized by high productivity and biodiversity 1, 2. ![]() Furthermore, it suggests that energy flows vary substantially between spider hunting modes and seasons. Consequently, this study underlines the importance of aquatic prey irrespective of the habitat specialization of spiders. Additionally, the elevated importance of high-quality lipids from aquatic origin during fall is indicated by elemental analyses pointing to an accumulation of lipids in October, which represent critical energy reserves during winter. Consumption of aquatic prey was highest in June and August, which is most pronounced in GH and WBs, with the latter feeding almost entirely on aquatic sources during this period. Averaged over the whole study period, web builders (WB) showed the highest proportions (78%) followed by ground hunters (GH, 42%) and vegetation hunters (VH, 31%). Mixing models showed that spiders’ diet consisted of 17–99% of aquatic sources, with no clear effect of habitat specialization. We expected that specialists would feed more on aquatic prey than their generalist counterparts. The spiders represent three hunting modes each consisting of a wetland specialist and a habitat generalist. To explore this, we assembled a large stable isotope dataset (n > 1000) of aquatic versus terrestrial sources and six spider species over four points in time adjacent to a lotic and a lentic system. However, little is known about the variation of aquatic insect consumption across spiders of different hunting modes, habitat specializations, seasons, and systems. Spiders are dominant consumers of these insect subsidies. Freshwater ecosystems subsidize riparian zones with high-quality nutrients via the emergence of aquatic insects.
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