Shifting habitat mosaics and fish production across river basins

Abstract

Watersheds are complex mosaics of habitats whose conditions vary across space and time as landscape features filter overriding climate forcing, yet the extent to which the reliability of ecosystem services depends on these dynamics remains unknown. We quantified how shifting habitat mosaics are expressed across a range of spatial scales within a large, free-flowing river, and how they stabilize the production of Pacific salmon that support valuable fisheries. The strontium isotope records of ear stones (otoliths) show that the relative productivity of locations across the river network, as both natal- and juvenile-rearing habitat, varies widely among years and that this variability is expressed across a broad range of spatial scales, ultimately stabilizing the interannual production of fish at the scale of the entire basin.

Dynamic contributions of intermittent and perennial streams to fish beta diversity in dryland rivers

“…The opposite was true in the Little Colorado River, characterized by low mainstem hydrologic connectivity, where perennial streams had more unique species composition. Despite the fact that the strength of our inferences are limited by including just two basins for comparison, these findings support the long recognized value of complementarity in conservation planning (Brennan et al, ; Vane‐Wright, Humphries, & Williams, ).…”

Drinking Locally: A Water 87Sr/86Sr Isoscape for Geolocation of Archeological Samples in the Peruvian Andes

“…Highland water samples displayed distinct 87 Sr/ 86 Sr than those from midelevation (yunga) and coastal zones, which demonstrates the homogenization of water strontium sources as rivers drain into the Pacific Ocean. Heterogeneity in water 87 Sr/ 86 Sr increases with watershed size, a finding that differs from the findings of Brennan et al (2019). In the Andes, the largest watersheds are located along the eastern slopes of the Andes and the Amazon Rainforest (Figure 2).…”

“…Hodell et al (2004) report that water body depth also influences 87 Sr/ 86 Srlocations with shallower water tables reflect upstream mixing, while locations with deeper water tables reflect more of the underlying bedrock signature. Watershed size also influenced 87 Sr/ 86 Sr variability, with larger watersheds leading to more homogenized 87 Sr/ 86 Sr in rivers (Brennan et al, 2019).…”

“…Predicting a continuous surface from linear features like rivers is also problematic, as spatial autocorrelation is constrained by distance to those rivers (Brennan et al, 2016). Particularly in the yunga and coastal Andes where settlements were constrained to river valleys, methods that constrain predictions to networks within specific watersheds (Bataille et al, 2014;Brennan et al, 2016Brennan et al, , 2019 would likely improve prediction accuracy for sites located within a walking-distance proximity to the river networks accessed by archeological human residents.…”

Spatial covariation of fish population vital rates in a stream network

“…Terui et al () showed that increased branching complexities of stream networks stabilised temporal metapopulation sizes of several fish species. Negative covariation in local vital rates likely enhances a portfolio effect (Schindler et al , Brennan et al ) in spatially structured populations. In fact, such an effect may be amplified by habitat heterogeneity among habitat patches.…”