Spatial relationships in a dendritic network: the herpetofaunal metacommunity of the Mattole River catchment of northwest California

Abstract

We investigated the aquatic and riparian herpetofauna in a 789 km2 river catchment in northwest California to examine competing theories of biotic community structuring in catchment stream networks. Research in fluvial geomorphology has resulted in multi‐scale models of dynamic processes that cyclically create, maintain, and destroy environments in stream networks of mountain catchments. These models have been applied to understanding distributions of invertebrates, algae, fishes and their habitats across entire basin networks, but similar approaches with herpetofauna are rare. We examined multi‐scale spatial patterns of multiple species as they related to variation in channel types, channel settings, and within‐channel attributes that result from these processes. From 83 reaches distributed randomly throughout the watershed, we distinguished four channel types: 1) high gradient with cascade structure; 2) 2–4% gradient with step‐pool structure controlled by moderately steep valleys; 3) slightly entrenched, lower gradient, plane‐bed structure; and 4) low gradient, shallow, unconfined, multiple or migrating pool/riffle channels in broad alluvial valleys. The composition of herpetofauna differed in five of six pair‐wise comparisons among these channel types, indicating a minimum of three distinct mesoscale assemblages. We used non‐parametric multiple regression (NPMR) to examine relationships at multiple spatial scales. NPMR revealed species‐specific associations with channel settings and within‐channel environments among species sharing the same sets of channel types. Morphological adaptations, biophysical limits and natural histories of each species best explained their associations with distinct sets of attributes surrounding and within channel types. While each set of species has similarly adapted to fluvial and geomorphic disturbance processes structuring channels at the mesoscale, species within each set have adapted to a unique set of attributes that are best discerned when their spatial relationships are examined across multiple spatial scales. We evaluated the various spatial patterns against hypotheses of stream community organization and metacommunity perspectives.

Abiotic habitat thresholds for salmonid over‐summer survival in intermittent streams

“…At a regional scale, spring-fed tributaries, critical for maintaining sufficiently high DO for salmonids, occupy a relatively small proportion of overall stream length (Jaeger and Olden 2012). Our results add to research on other taxa that suggests spring-fed refugia within intermittent streams can support high densities of imperiled organisms (Welsh andHodgson 2011, Bogan et al 2013). Our results also suggest that, to function as a sanctuary reach through periods of drought, a spring-fed stream must also feature pools that are large enough to maintain pockets of adequate DO through periods of drydown, or that have continuous hyporheic flow through the pools to prevent source depletion through respiration and stimulate oxygen reaeration and mixing through the pool.…”

Environmental factors associated with amphibian breeding in streams and springs: effects of habitat and fish occurrence

“…Interactions between stream-dwelling amphibians have received less attention than those among ponddwelling species. Communities of amphibians may be quite complex in river catchment basins (Welsh and Hodgson, 2011) and both pollution and human habitat fragmentation may affect them (Kupferberg et al, 2012). One of the main factors discriminating lotic and lentic habitats is the availability of food: stream amphibian larvae often have little zooplankton or phytoplankton for feeding (Gillespie et al, 2004).…”

Frogs, Fish and Forestry: An Integrated Watershed Network Paradigm Conserves Biodiversity and Ecological Services

“…Our findings in the Mattole [53] serve to illustrate some of these relationships. We used ordination analysis to determine channel types in the Mattole and discerned four distinct types (Figure 9).…”

“…Species depicted are those distributed primarily in colluvial (I and II), alluvial (III and IV), or in all four channel types; in several cases species were found in much greater abundances in types III and IV (not shown). For details see Welsh and Hodgson [53]; Table 4, Appendix I.…”

“…In more recent research in the Mattole watershed [53] we combined data from the tributary study [51] with those from the main stem river. The objective of this second study was to examine how the distributions of the herpetofauna related to network disturbance processes across the entire catchment.…”