Introduction
β-diversity (site-to-site variation in species composition) as a method
to quantify the species assembly pattern has provide insights into the
processes that create and maintain the compositional variation of
natural communities (Whittaker, 1960,Moritz et al ., 2001; Grahamet al ., 2006), β-diversity of biological communities along
biological gradients is a long debated focal topic for ecologists and
bio-geographers (Routledge, 1977; Harrison et al. , 1992).
Differences in β-diversity occurring along gradients are often used to
infer variation in the processes of structuring communities. Recent
studies suggested the driving forces of β-diversity was caused by a
series of combined mechanisms that affect these local community assembly
processes interactively with different relative contributions among
bio-geographical regions (Mori & Seidl, 2018). Generally, Species
relationships in the community can be conceived in terms of a
multidimensional coordinate system, the axes of which are the various
resource gradients, and those gradients usually can be categorized as
focusing on two major components: biotic and abiotic processes (Sextonet al. ,2009).
In nature, the influence of biotic and abiotic factors shaping species
community are often varying in time and spatial scale, and disentangling
the relative influences of these factors is not always a straightforward
process. Biotic interactions, which including interspecific competition,
mutualism, and predation/host relationships, may modify either the
resource availability or the local abiotic environment with potentially
contrasting consequences on abundance, and both positive and negative
interactions may affect species assemblage through inhibiting or
facilitating species establishment, individual growth and population
size (Holt 2009; Svenning et al. 2014). A good deal of examples from the
ecological literatures documented that these interactions are not static
in space and can be linked with the impacts of changing climate via
different complicated ways (Braschler & Hill 2007; Gilman et al ,
2010). And a part of these cases were elaborated as follows. Whittaker
proposed a conceptual framework in which abiotic factors (temperature
and precipitation) explained the distribution of terrestrial biomes of
the world (Whittaker 1975). Further more, the idea that climate is the
dominant factor shaping species distributions at broad scale is
conceived to explain the correlation of climate and species occurrence
patterns observed at a comparable spatial resolution (Woodward 1987).
Different with the broad spatial scale, Soberón & Nakamura claimed that
the pattern of fine spatial resolution is created by biotic interactions
(Soberón & Nakamura 2009). This idea is also verified by Pearson &
Dawson (2003), who stated that biotic interactions are expected to play
a role in shaping species distributions only over local extents. All of
these perspectives imply that the key point of the comparative influence
of biotic and abiotic process for species assembly rely on scale.
From the literature, approximately 500,000 known species on the earth is
herbivorous insects, which represent nearly a quarter of all terrestrial
macroscopic biodiversity (Daly, Doyen, & Purcell, 1998; Southwood,
1973;). The intimate association with land plants (especially
angiosperms) might be the dominating driving force of herbivorous
insects’ extraordinary diversification (Farrell, 1998; Strong, Lawton,
& Southwood, 1984; Marvaldi, Sequeira, O’Brien, & Farrell, 2002;
Mitter, Farrell, & Wiegmann, 1988). There are a great deal of
observations showing that most herbivorous insects only feed on one or
few related plant species and showed narrow host range; adaptation
towards different host-plant species can potentially generate ecological
specialization in plant-feeding insects and, subsequently, species
formation. If plant diversity influences insect speciation, we can
expect that insect community composition will be strongly correlated
with host-plant community composition. This should be observable at the
level that insect community composition will co-vary with the host plant
community composition.
For arthropod insect communities, substantial compositional change is
prevalent between regions along abiotic gradients within regions (Hoisset al. , 2012; Pellissier et al. , 2013) and between
habitats differing in plant community composition under the conditions
that evolved host specialization (Siemann et al. , 1998; Schafferset al. , 2008). If insect speciation results from allopatric host
shifts of specialized insect species, insect community composition
variation should be associated with plant community composition
variation in a predictable manner (Siemann et al. , 1998;
Schaffers et al. , 2008; Pellissier et al. , 2013). However,
although the matching patterns could indicate speciation through host
shifts or allopatric insect speciation with subsequent host
specialization, it could also indicate parallel responses to broad
abiotic gradients. Therefore, patterns resulting from parallel responses
to macroclimatic gradients are often difficult to distinguish from
patterns resulting from evolutionary associations (Hawkins & Porter,
2003). A potential approach to tease these two factors apart is to
examine patterns of association between plant and insect β-diversity at
different spatial scales (Kemp et al. , 2017). If both patterns
result from insect-host specialization, plant and insect β-diversity
should be correlated at fine, as well as broad spatial scales. However,
if patterns result from parallel responses to broad abiotic gradients,
β-diversity patterns should only be correlated at broad spatial scales
(Kemp et al. , 2017).
Longhorn beetles belongs to the order Coleoptera of the class Insecta,
presenting a period in their life cycle (mainly larval stage) feeds on
the xylem of plants or trees. It is estimated that there are more than
26000 species of longhorn beetles in the world, the relationships
between longhorn beetles and their host plants are often quite specific,
but there is a great range in the breadth of host tree species that
might be used by the larvae of different species (Hanks, 1999). Longhorn
beetle is not only an important component of ecological biodiversity,
but also has vital effects in the sustaining and balancing of forest
ecosystem. They are not only the decomposer of organic matter such as
wood residues during forest renewal, but also the pollinators of some
plant species. Since the diet habits of the longhorn beetle display
attributes of host specificity, exploring the β-diversity of insect
communities in different climatic zones and habitats will not only be
helpful to understand the regional geography and renewal process of
forest vegetation, but also contributes to understand the mechanism of
maintenance and cycling of natural forest vegetation (Arias et al. 2008;
Strong et al.1984; Wagner 2000).
The effect of plant diversity and structural heterogeneity of habitat on
longhorn beetle assemblages within a local scale have been heavily
studied (Meng et al. , 2013; Gatti et al. , 2018), but a
cross regional comparison of β-diversity of longhorn beetle communities
and their association with plant species along a broad environmental
gradient has rarely been reported. Our specific goal of the study was to
determine the contribution of tree species and phylogeny to the long
horn beetle β-diversity distribution models along the increasing spatial
extent and climatic gradient across Yunnan province in SW China, the
Indo-Burma biodiversity hotspots of the eastern Himalayas (Myerset al. , 2000). We hypothesize that: (1) species β-diversity of
the longhorn beetle community is comparable and scale dependent to that
of plant species across spatial space from the tropical to temperate
regions; (2) biotic (insect and host plant interaction) and abiotic
(climatic gradients) factors collaboratively shaped longhorn beetle
community composition along various spatial scales; (3) the relative
importance of abiotic and biotic variation explaining the longhorn
beetle community composition vary by spatial scale, and biotic
interactions have prominent effect to longhorn beetle community
composition at local scale while macroclimatic gradients impose the most
control on it at macro-scale.