1. Seasonal variation in resource availability can have strong effects on life histories and population densities. Emergent rocks (ERs) are an essential oviposition resource for multiple species of stream insects. The availability of ERs depends upon water depth and clast size, which vary with discharge and river geomorphology, respectively. Recruitment success for populations may depend on whether peak egg-laying periods occur at times when ERs are also abundant. For multiple species that oviposit on ERs, we tested whether seasonal fluctuations in ER abundance were concurrent with oviposition phenology. We also tested whether high discharge drowned ERs for sufficiently long periods to preclude egg laying, and whether this problem varied between rivers differing in channel morphology and particle size distribution.
2. We obtained a continuous timeseries of water level (WL) measured every 30 min for 2 years at sites on three rivers in south-eastern Australia with similar hydrology but different geomorphology. A relationship between WL and ER numbers was determined empirically at each site and these relationships were used to predict ER availability over the 2 years. Egg masses of 10 species of caddisflies were enumerated each month for a year in one river to establish oviposition phenology.
3. Abundance of ERs was inversely related to discharge in all three rivers. ERs were most abundant during autumn and scarce during spring. Site-specific geomorphology resulted in skewed or multimodal distributions of ER abundance each year. Between years, catchment-scale hydrometeorology mediated patterns of ER availability, despite the close proximity of sites. Temporal variance in ER availability was not consistently correlated with mean WL or WL variance. ER variance increased with WL variance, when WL was below a threshold equivalent to mean annual WL. Above this threshold, most ERs were likely to be submerged.
4. Oviposition phenology varied strongly among the 10 species of caddisflies, with egg-laying ranging from 1–2 months to year-round. Temporal variations in ER and egg mass abundance were not correlated for most species. Below a threshold minimum number of ERs, egg masses were highly crowded onto the few available ERs, which is evidence that ERs were in short supply. For five species, high egg mass abundance was positively associated with periods of the year when the time above the threshold number of ERs was high. Unusually, two species laid most egg masses during winter and when the time above this threshold was short. Three species showed no association between egg mass abundance and time above this threshold; two of these species laid eggs year-round.
5. Regional hydrometeorology controlled the availability of ERs, but between-river differences were sufficient to deliver different outcomes in the availability of oviposition sites between years and seasons. Caddisflies were rarely prevented from laying eggs but periods when ERs were in short supply created crowding, which may be associated with negative fitness effects on hatching larvae. Geomorphological controls on availability of oviposition resources may have strong implications for the coexistence of species that overlap in egg-laying phenology.

中文翻译：

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对产卵栖息地的水文控制与一些石蛾的产卵物候有关

1. 资源可用性的季节性变化会对生活史和人口密度产生强烈影响。涌现岩 (ER) 是多种河流昆虫必不可少的产卵资源。ER 的可用性取决于水深和碎屑大小，它们分别随流量和河流地貌变化。种群的招募成功可能取决于产卵高峰期是否出现在 ER 也很丰富的时候。对于在 ER 上产卵的多个物种，我们测试了 ER 丰度的季节性波动是否与产卵物候同时发生。我们还测试了高排放量是否会在足够长的时间内淹没 ER 以阻止产卵，以及这个问题是否因河道形态和粒度分布不同的河流而异。
2. 我们在澳大利亚东南部具有相似水文但不同地貌的三条河流的地点获得了连续两年的水位 (WL) 时间序列，每 30 分钟测量一次。在每个站点凭经验确定 WL 和 ER 数量之间的关系，这些关系用于预测 2 年内的 ER 可用性。在一年中，每个月对一条河流中 10 种石蛾的卵群进行计数，以建立产卵物候。
3. ERs 的丰度与所有三条河流的流量呈负相关。ERs 在秋季最为丰富，而在春季则稀少。特定地点的地貌导致每年 ER 丰度的偏斜或多峰分布。几年之间，流域尺度的水文气象介导了 ER 可用性的模式，尽管站点很近。ER 可用性的时间方差与平均 WL 或 WL 方差不一致。当 WL 低于等于平均年度 WL 的阈值时，ER 方差随 WL 方差而增加。高于此阈值，大多数 ER 可能会被淹没。
4. 10 种石蛾的产卵物候变化很大，产卵时间从 1-2 个月到全年不等。大多数物种的 ER 和卵质量丰度的时间变化不相关。低于最低 ER 数量的阈值，卵块高度拥挤在少数可用的 ER 上，这证明 ER 供不应求。对于五个物种，高鸡蛋质量丰度与一年中高于 ER 阈值数量的时间高的时期呈正相关。不同寻常的是，有两个物种在冬季产卵量最多，而且超过这个阈值的时间很短。三个物种的卵子质量丰度与高于此阈值的时间之间没有关联；其中两个物种全年产卵。
5. 区域水文气象控制了 ER 的可用性，但河流之间的差异足以在年份和季节之间产生不同的产卵地点可用性结果。石蛾很少被阻止产卵，但是当 ER 供不应求时会造成拥挤，这可能与孵化幼虫的负面健康影响有关。对产卵资源可用性的地貌控制可能对产卵物候重叠的物种的共存具有重要意义。