DOI: 10.5061/dryad.t4b8gthxk
title: Data from: Contribution of small isolated habitats in creating refuges from biological invasions along a geomorphological gradient of floodplain waterbodies

description: 1. Habitat fragmentation, which involves habitat size reduction
 and isolation, is a major cause of biodiversity decline. However, interest
 in small isolated habitats has increased among ecosystem managers because
 these fragments can serve as remnant refuges for unique and/or endangered
 species in human-altered landscapes. 2. In a fragmented
 floodplain of northern Japan, we demonstrate how habitat fragmentation and
 habitat quality shape the refuges for a unique endangered minnow
 (Rhynchocypris percnurus sachalinensis) from biological invasions. We
 focused on two invasive minnows, topmouth gudgeon (Pseudorasbora parva)
 and rosy bitterling (Rhodeus ocellatus ocellatus), which are the dominant
 invasive species. By using a graph theoretical approach and structural
 equation modeling, we elucidated the relationships among habitat
 fragmentation, habitat quality and the abundance of invasive minnows with
 the endangered swamp minnow. 3. We found that the invasion of
 topmouth gudgeon, which has a high mobility and environmental tolerance,
 negatively affected swamp minnow populations. The invasive species may
 outcompete the native species in their overlapping trophic niche.
 4.  Analyses indicated that habitat fragmentation
 (decreasing habitat size and connectivity) indirectly and positively
 affected the population abundance of swamp minnow by reducing the
 potential for invasion by topmouth gudgeon. We further found an
 interaction between the indirect effects of habitat fragmentation and
 local habitat quality: the indirect effects became more apparent in the
 relatively deeper habitats that were of better quality for natives. This
 result was likely attributed to the strong control effect of the abiotic
 stressor. Interspecific competition between the two minnows would be
 masked in shallow ponds because the native populations are primarily
 restricted by the abiotic factor, and its abundance is inherently limited
 regardless of pressure by invaders. 5.  In fragmented
 landscapes, evenly conserving all small fragments within a limited budget
 is difficult. The change in importance of small isolated ponds across a
 pond-depth gradient suggests that conservation priorities for small
 fragments should be established by considering local habitat quality. Our
 findings do not justify habitat fragmentation but suggest that both
 landscape-scale and local-scale perspectives synergistically aid in the
 management of biological invasions in modified habitat networks.
description: <strong>Definitions of the variable headings</strong> Site：ID of study sites River：River name for each study site <em>Pseudorasbora parva</em>_CPUE：Relative abundance of topmouth gudgeon <em>Phoxinus percnurus</em>_CPUE：Relative abundance of swamp minnow <em>Rhodeus ocellatus</em>_CPUE：Relative abundance of rosy bitterling dIIC_15：Delta Integral Index of Connectivity (threshold connectivity distance = 15 km) Vegi：Vegetation cover ratio Depth：Pond depth Min DO：Minimum dissolved oxygen EC：Electrical conductivity PH：PH   *Note that all variables are log or arcsine transformed.