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Additive and non‐additive effects from a larger spatial scale determine small‐scale densities in a web spider Neriene brongersmai
Author(s) -
Takada Mayura,
Miyashita Tadashi
Publication year - 2004
Publication title -
population ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 59
eISSN - 1438-390X
pISSN - 1438-3896
DOI - 10.1007/s10144-004-0187-7
Subject(s) - intraspecific competition , spider , biology , spatial ecology , interaction , population density , ecology , scale (ratio) , density dependence , population , competition (biology) , demography , geography , agronomy , cartography , sociology
We examined 15 populations of Neriene brongersmai , a common sheet‐web spider inhabiting cedar forest floor, to find out how density at a small spatial scale (patch level) is determined by processes operating at this scale as well as those from a larger spatial scale (population level). Here we focus on two types of large‐scale effects that may influence small‐scale density: an additive effect that changes the density at patch level; and a non‐additive effect that changes the relationship between the density and its limiting factor at the patch level. ANCOVA showed that patch‐level density of this spider was positively correlated with web‐site availability at this level, but the density with a given amount of web‐site differed among populations (cedar forests), indicating the existence of an additive large‐scale effect. Multiple regression analysis showed that web‐site availability at a population level explained the additive large‐scale effect well, but prey availability and forest size did not. It seemed likely that increased web‐site availability may have reduced the mortality of spiders while moving to a new web‐site, and hence increased population density. A non‐additive large‐scale effect was also revealed: i.e. the relationship between density and web‐site availability at the patch level tended to be stronger in populations with a greater additive large‐scale effect. Higher intraspecific competition for web‐sites in these populations appeared to have strengthened this relationship.