Many species living in deeper lentic ecosystems exhibit daily movements that cycle through the water column, generally referred to as diel vertical migration (DVM). In this study, we applied bioenergetics modelling to evaluate growth as a hypothesis to explain DVM by bull trout (Salvelinus confluentus) in a thermally stratified reservoir (Ross Lake, WA, USA) during the peak of thermal stratification in July and August. Bioenergetics model parameters were derived from observed vertical distributions of temperature, prey and bull trout. Field sampling confirmed that bull trout prey almost exclusively on recently introduced redside shiner (Richardsonius balteatus). Model predictions revealed that deeper (>25 m) DVMs commonly exhibited by bull trout during peak thermal stratification cannot be explained by maximising growth. Survival, another common explanation for DVM, may have influenced bull trout depth use, but observations suggest there may be additional drivers of DVM. We propose these deeper summertime excursions may be partly explained by an alternative hypothesis: the importance of colder water for gametogenesis. In Ross Lake, reliance of bull trout on warm water prey (redside shiner) for consumption and growth poses a potential trade-off with the need for colder water for gametogenesis.
Resource managers increasingly use habitat suitability map products to inform risk management and policy decisions. Modeling habitat suitability of data-poor species over large areas requires careful attention to assumptions and limitations. Resulting habitat suitability maps can harbor uncertainties from data collection and modeling processes; yet these limitations are not always transparent to resource managers, who increasingly rely on maps for spatial planning and risk assessment purposes. Interpretation of habitat suitability maps can be improved by visually communicating model uncertainty and data foundations. We applied Bayesian networks (BNs) to a small, marine dataset to model the probability of occurrence (PO) of benthic macrofauna. We also used BNs to create maps displaying model parameter uncertainty and data limitations. We developed BN models for three macrofauna species: a marine gastropod, Aystris gausapata, a marine bivalve, Axinopsida serricata, and a marine worm, Sternaspis fossor. We produced three map products from the BN models of each species: (1) a habitat suitability map of the PO projected from regional predictor variables; (2) an uncertainty map, displaying statistical variance of model predictions of occurrence probability; and (3) an experience map, displaying the empirical basis for PO predictions (equivalent sample size). Map results showed occurrence probability to be high and widespread for Ax. serricata, low to moderate and more limited to deeper offshore areas for Ay. gausapata, and low to high in shallow sandy regions and deeper silty regions, respectively, for S. fossor. The uncertainty and experience maps for each species helped identify regions to prioritize for future sampling. Our results are the first to show that BNs can effectively model habitat suitability of benthic macrofauna, and our detailed methods can be applied to a variety of taxa and systems. Visually describing statistical model uncertainty and equivalent sample size in map format improves interpretation of habitat suitability map predictions and supports place-based risk management of marine management.
Habitat selection is a fundamental component of community ecology, population ecology, and evolutionary biology and can be especially important to species with complex annual habitat requirements, such as migratory birds. Resource preferences on the breeding grounds may change during the postfledging period for migrant songbirds, however, the degree to which selection changes, timing of change, and whether all or only a few species alter their resource use is unclear. We compared resource selection for nest sites and resource selection by postfledging juvenile ovenbirds (Seiurus aurocapilla) and Acadian flycatchers (Empidonax virescens) followed with radio telemetry in Missouri mature forest fragments from 2012−2015. We used Bayesian discrete choice modeling to evaluate support for local vegetation characteristics on the probability of selection for nest sites and locations utilized by different ages of postfledging juveniles. Patterns of resource selection variation were species-specific. Resource selection models indicated that Acadian flycatcher habitat selection criteria were similar for nesting and dependent postfledging juveniles and selection criteria diverged when juveniles became independent from adults. After independence, flycatcher resource selection was more associated with understory foliage density. Ovenbirds differed in selection criteria between the nesting and postfledging periods. Fledgling ovenbirds selected areas with higher densities of understory structure compared to nest sites, and the effect of foliage density on selection increased as juveniles aged and gained independence. The differences observed between two sympatric forest nesting species, in both the timing and degree of change in resource selection criteria over the course of the breeding season, illustrates the importance of considering species-specific traits and postfledging requirements when developing conservation efforts, especially when foraging guilds or prey bases differ. We recommend that postfledging habitat selection be considered in future conservation efforts dealing with Neotropical migrants and other forest breeding songbirds.
La historia de las truchas del Pacífico, pertenecientes al género Oncorhynchus, es una historia muy interesante que se basa en la persistencia y diversificación de sus especies debido, en gran parte, al dinamismo propio que existe en su medio ambiente. Desde el oeste de Norteamérica, extendiéndose hasta el este de Asia, las truchas del Pacífico han experimentado la influencia de los avances y retrocesos de glaciares, vulcanismo, condiciones extremas en el caudal de los ríos, al igual que eventos geotectónicos, que han permitido la formación de cordilleras y mesetas. Dichos eventos son los que han determinado el curso actual de los ríos modernos. En el oeste de Norteamérica, entre las especies de trucha del Pacífico se incluyen la trucha degollada (O. clarkii ssp.), la arcoiris (O. mykiss ssp.), la dorada (O. aguabonita ssp.), la trucha gila (O. gilae), la trucha Apache (O. apache) y la trucha dorada Mexicana (O. chrysogaster), además del complejo diverso de truchas de la Sierra Madre Occidental (SMO) en México que aún no son clasificadas taxonómicamente.