Examine the influence of habitat diversity and substratum on the composition of macroinvertebrate communities from riverine systems

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Examine the influence of habitat diversity and substratum on the composition of macroinvertebrate communities from riverine systems

Introduction

There have been and continues to be attempts to explain spatial and temporal patterns of diversity in riverine systems (Death and Winterbourne, 1995) and there have been numerous studies aimed at investigating macroinvertebrate community variations.

Macroinvertebrate distributions in streams are determined by variations of many factors such as habitat and food availability, substratum, hydraulic structure and channel morphology, which create distinct morphological units within streams. (Church 1996; Giller and Malmqvist, 1998). Three main habitat types have been identified: erosional, depositional and with macrophytes, habitats which are more commonly referred to as riffles, pools and runs. (Jenkins et al., 1984; Buffagni et al., 2000)

The majority of academic study has concluded that the run-riffle habitat supports the highest number of taxa while the lowest is that of the backwater habitats and that riffles are more diverse than pools (Brown and Brussock, 1991[2]; Logan and Brooker, 1983; Buffagni et al., 2000; Hynes, 1970: Scullion et al., 1982; Armitage et al., 1974; Death and Winterbourne, 1995; Costa et al., 2008).

Although some studies in the mountain stream channel form reported equal or more species abundance and diversity in depositional pool areas (Mcculoch, 1986; Egglishaw and Mackay, 1966; Armitage et al., 1974; Hynes et al., 1976).

Species distribution has been found to vary considerably with specific species displaying preferences to certain habitats and the conditions they provide. For example a difference is seen in the dominant abundance of chironomids in pools and Simuliids in riffles were discovered, along with more riffle and run taxa such as Ephemeroptera, Trichoptera, Plecoptera, and Oligochaeta. (Scullion)

Most Baetids, Simuliidae and all Plecoptera were found to be more abundant in riffles whereas Chironomidae, Dytiscidae and Leptophlebiidae apparently always more common in pools (Armitage et al., 1974). Plecoptera, which are sensitive to low oxygen concentrations due to a lack of extensive gills indicate favourable conditions in riffles, where oxygen concentration is higher. (Scullion et al., 1982).

Many species display exclusivity and adaptations to certain habitats, such as Hydropshyche in riffles or coleopteran, Odonata and Hirudinae in pools. (McCulloch, 1986) found more taxa restricted to pools, however the number of taxa restricted to riffles and faster flowing conditions is generally greater than that of pools (Logan & Brooker 1983, Brown and Brussock, 1991[2]),

At local scales, the spatial variation of organisms is driven often by their behaviour as the search for and the distribution of resources, which is clearly influenced by substrate characteristics (Boyero, 2003).

Substrate is one of the prime factors governing macroinvertebrate compositions with two main variable features, stability and heterogeneity, along with coarse and fine substrates which prove suitable for different taxa (Brown n Brss 11). Substrate diversity or heterogeneity along with high hydraulic variability provides high numbers of feeding niches and micro habitats, resulting in positive relations to abundance, diversity and evenness. (Pedersen and Friberg, 2007; Beisel et al.; Boyero, 2003; Rice et al., 2001)

Substrate stability or consolidation is another key factor. It is proposed unstable unconsolidated riffles had higher abundance and species richness but lower evenness than compact riffles (Pederson and Friberg, 2007), alternatively Rice suggests structured substrates provides a more attractive habitat to benthic fauna as it represents areas of least disturbance during flood events (Rice et al., 2001).

Pools often lack coarse gravel substrate and this can mean fewer interstitial refugia are available resulting in higher predation vulnerability than riffles (Rice et al., 2001). Williams & Mundie (1978) suggest medium size gravel supports the greatest number and biomass although scullion believes otherwise with little difference in particle size compostion of bed materials in pools and riffles.

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McCulloch’s (1986) contrasting study of sandy bed rivers found that the instability of sandy substrate in riffles limited colonization by benthos and depressing the numbers of certain species. Grain roughness is another contributing factor as it defines near bed hydraulic conditions such as turbulence and shear stress and also influences the retention of detritus, a key factor affecting abundance according to Fahy (1975), which effect organisms’ ability to move position and feed effectively. (Rice et al., 2001)

As most benthic animals are functionally sessile, they depend on flow to supply physiological needs other of their requirements such as food ...

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