Academic journal article Estonian Journal of Ecology

Influence of Environmental Factors on the Distribution of Caddisfly (Trichoptera) Communities in Medium-Sized Lowland Streams in Latvia/Keskkonnatingimuste Moju Ehmestiivaliste (Trichoptera) Koosluste Levikule Lati Keskmise Suurusega Madalikujogedes

Academic journal article Estonian Journal of Ecology

Influence of Environmental Factors on the Distribution of Caddisfly (Trichoptera) Communities in Medium-Sized Lowland Streams in Latvia/Keskkonnatingimuste Moju Ehmestiivaliste (Trichoptera) Koosluste Levikule Lati Keskmise Suurusega Madalikujogedes

Article excerpt

INTRODUCTION

Caddisflies (Trichoptera) are among the most diverse primary aquatic insects worldwide, exceeded in the number of species only by aquatic Diptera (Mackay & Wiggins, 1979). There are about 1000 more caddisfly species than the other primary aquatic orders combined (Grimaldi & Engel, 2005). Ecological opportunities of caddisflies are explainable by their ability to build portable cases, nets, and shelters from mineral or organic particles using silk secretion (Mackay & Wiggins, 1979). Caddisfly larvae inhabit a wide range of aquatic microhabitats and virtually occupy all functional feeding groups from filtering collectors to carnivores (Wallace & Merritt, 1980).

Trichoptera larvae are important and beneficial components of the trophic dynamics and energy flow in streams they inhabit (Resh & Rosenberg, 1984). They are one of the best indicator groups of macroinvertebrates, because caddisfly larvae have essential advantages; for example, they have a limited mobility and a relatively long life span, which allow for an easy integration on spatial and temporal scales; they present reasonably cosmopolitan distributions, which enables comparative studies at least at a regional scale; their numerical predominance allows easy sampling and conclusions regarding quantitative distribution patterns (Dohet, 2002).

Streams are heterogeneous and hierarchically organized ecosystems (Frissell et al., 1986; Allan, 1995). All caddisfly families are represented in running waters, but many genera and the majority of species have restricted distribution along the stream continuum (Mackay & Wiggins, 1979). The River Continuum Concept (RCC) (Vannote et al., 1980) proposes that from headwaters to lower reaches, the physical variables within a stream system present a continuous gradient of physical conditions. The longitudinal variability in ecological conditions in streams is due to stream size (headwaters, medium-sized streams, and large rivers), as is the attendant variability in the structural and functional attributes of lotic insect communities (Vannote et al., 1980; Ward, 1992).

Spatial pattern is a fundamental theme in aquatic ecology (Levin, 1992), and multiscale spatial studies of macroinvertebrates have been common since the 1980s (e.g. Boyero, 2003; Sandin & Johnson, 2004). Poff (1997) suggested that species could be described in terms of their functional relationships to various habitat features, which can be defined at different spatial scales and organized hierarchically. Scaled habitat features perform like filters that influence the probability that individual species with specific functional characteristics are able to persist in a local community. Spatial distribution patterns of lotic caddisfly larvae have been well established (e.g. Urbanic et al., 2005; Galbraith et al., 2008). Most studies have focused on species-specific aggregation patterns (Schmera, 2004). The scale at which the lotic ecosystem is observed is important when determining which factors influence its structure (Sandin & Johnson, 2004) and function. It is not easy to categorize substrates on a linear scale as physical variables (Allan, 1995). Streambed substratum also affects the distribution and abundance of lotic invertebrates (Gurtz & Wallace, 1986). It is generally assumed that the scale at which communities exhibit the greatest variation is the scale over which important physical/chemical gradients or biotic interactions control assemblage composition (Li et al., 2001).

Seasonal, local (e.g. reach), and stream-order (e.g. between streams by size) differences in inputs, production, and storage of food resources provide spatially and temporally variable systems from which macroinvertebrates derive their nutrition (Cummins & Klug, 1979). Macroinvertebrate faunal richness tends to be higher in a spatially heterogeneous environment composed of numerous substrates with elevated patchiness, thus offering a great number of niches for invertebrates and also a greater number of refugia from disturbance and predation (Beisel et al. …

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