Intraspecific population diversity (specifically, spatial asynchrony of population dynamics) is an essential component of metapopulation stability and persistence in nature. In 2D systems, theory predicts that metapopulation stability should increase with ecosystem size (or habitat network size): Larger ecosystems will harbor more diverse subpopulations with more stable aggregate dynamics. However, current theories developed in simplified landscapes may be inadequate to predict emergent properties of branching ecosystems, an overlooked but widespread habitat geometry. Here, we combine theory and analyses of a unique long-term dataset to show that a scale-invariant characteristic of fractal river networks, branching complexity (measured as branching probability), stabilizes watershed metapopulations. In riverine systems, each branch (i.e., tributary) exhibits distinctive ecological dynamics, and confluences serve as "merging" points of those branches. Hence, increased levels of branching complexity should confer a greater likelihood of integrating asynchronous dynamics over the landscape. We theoretically revealed that the stabilizing effect of branching complexity is a consequence of purely probabilistic processes in natural conditions, where within-branch synchrony exceeds among-branch synchrony. Contrary to current theories developed in 2D systems, metapopulation size (a variable closely related to ecosystem size) had vague effects on metapopulation stability. These theoretical predictions were supported by 18-y observations of fish populations across 31 watersheds: Our cross-watershed comparisons revealed consistent stabilizing effects of branching complexity on metapopulations of very different riverine fishes. A strong association between branching complexity and metapopulation stability is likely to be a pervasive feature of branching networks that strongly affects species persistence during rapid environmental changes.

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The meanders and floodplains of the Kushiro River were restored in March 2011. A 1.6-km stretch of the straightened main channel was remeandered by reconnecting the cutoff former channel and backfilling the straightened reach, and a 2.4-km meander channel was restored. Additionally, flood levees were removed to promote river-floodplain interactions. There were four objectives of this restoration project: to restore the in-stream habitat for native fish and invertebrates; to restore floodplain vegetation by increasing flooding frequency and raising the groundwater table; to reduce sediment and nutrient loads in the core wetland areas; to restore a river-floodplain landscape typical to naturally meandering rivers. In this project, not only the natural landscape of a meandering river but also its function was successfully restored. The monitoring results indicated that these goals were likely achieved in the short term after the restoration. The abundance and species richness of fish and invertebrate species increased, most likely because the lentic species that formerly inhabited the cutoff channel remained in the backwater and deep pools created in the restored reach. In addition, lotic species immigrated from neighboring reaches. The removal of flood levees and backfilling of the formerly straightened reach were very effective in increasing the frequency of flooding over the floodplains and raising the water table. The wetland vegetation recovered rapidly 1 year after the completion of the meander restoration. Sediment-laden floodwater spread over the floodplain, and approximately 80-90% of the fine sediment carried by the water was filtered out by the wetland vegetation.

The management of population size and genetic diversity in fragmented landscapes is the central issue in conservation biology. Functional connectivity between remnant habitat patches affects these parameters. However, the functional connectivity for genetic diversity would be characterised by a greater spatial scale than population size even within the same habitat network. The reason for this difference is that while dispersal frequency generally decreases with increasing distance, only a few immigrants may effectively contribute to gene flow, whereas a certain number of dispersers may be required to influence population abundance. Here, we investigated the effects of habitat network structures on population abundance and genetic diversity of the ninespine stickleback, Pungitius pungitius, in remnant wetland ponds in northern Japan. We tested (i) whether both population abundance and genetic diversity are positively related not only to habitat size but also to connectivity and (ii) whether the dispersal effect extends to greater spatial scales in genetic diversity than in population size. We employed a graph theoretical index to measure the degree of pond connectivity. This index can evaluate the connectivity threshold distance above which individuals cannot disperse and clarify the difference in the spatial scale of effective dispersal between population abundance and genetic diversity. Pond connectivity significantly affected the spatial variation of both population abundance and genetic diversity. In contrast, pond size was related only to population abundance. As we predicted, the connectivity threshold distance for genetic diversity was more than two times greater than that for population abundance (12.5km versus 5km, respectively). Our findings indicate that the landscape managers should consider various spatial scales as a conservation unit for the management of a habitat network in accordance with the conservation targets that they establish. We also found that small artificial agricultural ditches and streams may play important roles in sustaining the population networks of wetland organisms

Anthropogenic noise is widespread, and growing evidence suggests that it can negatively affect animals through many different mechanisms including masking of cues and signals, distraction, and aversion to noise. Acoustic masking has received the most attention from researchers and recent evidence suggests that masking effects can be mitigated by alteration of signal frequencies or amplitudes by signalers. Additionally, alteration can be a learned response via prior experience with noise exposure. However, it remains unclear whether distraction or aversive effects due to noise can be mitigated by prior experience with noise, especially among signal receivers. Here, we addressed this gap by separating mechanisms of noise disturbances on female phonotaxis towards male advertisement calls in anurans. To do this, we experimentally examined phonotaxis of gravid females that differ in their prior experience with noise under three acoustic manipulations: spectrally overlapping and non‐overlapping noise that either mask or do not mask male advertisement calls respectively, plus a silent control. We confirm two experience‐dependent responses of noisy‐site individuals relative to quiet‐site individuals: faster initiation of phonotaxis under non‐overlapping noise and a stronger aversive response against overlapping noise. However, we showed that, for both noisy‐ versus quiet‐site individuals, both overlapping and non‐overlapping noise treatments resulted in delayed initiation and disorientation of phonotaxis relative to silent control treatments. Our study provides the first evidence to demonstrate that, although prior experience appears to mitigate the negative effects of distraction or aversion to noise, prior experience falls short of fully compensating for disrupted orientation through phonotaxis. Additionally, although most studies have emphasized masking of biologically relevant cues and signals as the most prominent mechanism by which noise negatively affects wild organisms, we show that non‐overlapping noise, which cannot cause signal and cue masking, can have negative consequences via distraction or aversive responses. This finding suggests that noise impacts could extend well beyond contexts involving acoustic cue detection and discrimination and deserves increased attention by researchers. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13130/suppinfo is available for this article.