1 Introduction
Understanding how fish assemblages are structured in lotic ecosystems is
one of the interesting aspects of community ecology and these knowledges
can provide useful information in diversity conservation and ecological
restoration (Araújo et al. 2009). The River Continuum Concept (RCC)
suggested longitudinal variations in physicochemical environment (e.g.,
width, depth, velocity, flow volume and temperature) influence
structural and functional characteristics of lotic aquatic communities
(Vannote et al. 1980). Species diversity often increase with the
upstream-downstream gradient, responding to the increased habitat
diversity and food availability (Lowe-McConnell 1975). Although the
original RCC developed for aquatic macroinvertebrates, similar patterns
have been found for fish assemblages in both temperate and tropical
regions (Hughes and Gammon 1987; Matthews 1998; Ferreira and Petrere Jr.
2009). Subsequent studies further found that large-scale landscape
position, such as stream order, stream size, link magnitude, confluence
link (C-link) and downstream link (D-link), are important factors in
structuring stream fish assemblage (Fausch et al. 1984; Osborne and
Wiley 1992; Fairchild et al. 1998; Smith and Kraft 2005; Mullen et al.
2011). For example, Fausch et al (1984) found fish assemblages changed
gradually with stream order. Smith and Kraft (2005) demonstrated that
confluence link and stream order were the stream network position
measures with the greatest influence on fish assemblages. Osborne and
Wiley (1992) observed downstream link explained the greatest portion of
the variance in fish species richness and suggested downstream processes
significantly influence the structure of fish assemblages. In addition,
seasonal variations in environmental conditions caused by periodic
flooding are expected to have significant impacts on stream fish
assemblages (Ostrand and Wilde 2002; He et al. 2017). Flooding can
increase the diversity and availability of habitat structures and food
resources, and then lead to changes in fish assemblage between dry and
wet seasons (Araújo et al. 2009). Therefore, the current consensus is
that stream fish assemblages are structured by a series of local and
regional factors operating at multiple spatial and temporal scales
(Matthews 1998; Jackson et al. 2001;
Vardakas et al. 2015). However, the
relative importance of these factors varies with environmental
variability, climate conditions, and nature of fish assemblage in the
survey area (Grossman et al. 1998; Jackson et al. 2001).
To date, spatial and temporal variations of stream fish assemblages have
been tested in numerous regions, including the North America (Ostrand
and Wilde 2002; Mullen et al. 2011), Latin America
(Silvano et al. 2000; Habit et al.
2007; Araújo et al. 2009; Fernandes et al. 2013), Europe (Pires et al.
1999;
Vardakas
et al. 2015) and South Asia (Bhat
2004). In recent years, similar studies have been also conducted in
China. However, nearly all these studies were concentrated in the
central and eastern regions (Yan et al. 2010; Li et al. 2012; He et al.
2017; Zhu et al. 2017). The southwest China, where raises the greatest
number of streams and rivers and supports the highest degree of fish
diversity, received little attention.
The Dabashan Mountains is located at the border area of Hubei province,
Chongqing municipality, Sichuan province and Shanxi province in the
southwest China. It is an important water source for many river systems.
The Jialing River and the Han River, which represent the largest
tributaries of the upper and middle Yangtze river respectively, both
originate from this region. Furthermore, the Dabashan Mountains harbors
a high level of biodiversity and species endemicity, which has been
listed as one of the 35 biodiversity conservation priority area of China
(Ministry of Ecology and Environment of People’s Republic of China
2010). Therefore, the Dabashan Mountains plays important roles in water
security and biodiversity conservation. Even so,
little information about the
distribution patterns of fish fauna in this region is available until
now. On the other hand, fish diversity in this region has been decreased
seriously due to the increased human activities, such as over-fishing,
hydropower station construction and water pollution (Zeng 1991). The
development of effective conservation strategies needs urgently to
understand the organization mechanisms of fish assemblages in this area.
Therefore, fish fauna and environmental features in mountain streams of
the Ren River, the largest tributaries of the upper Han River, were
investigated in this study. The main objective was to test whether and
how
fish
assemblages in this mountain river vary at different spatial and
temporal scales. Furthermore, we would like to identify the key
environmental factors that contributed most to the observed
spatial-temporal patterns of fish assemblage structure. We believe these
studies can help us to understanding how fish assemblage structured in
such mountain river systems and then provide valuable information in
future fish conservation and management.
2
METHODS