Winter and summer upwelling modes and their biological importance in the California Current Ecosystem

Analysis of monthly coastal upwelling intensities revealed two seasonal and biologically relevant upwelling ‘modes’ in the California Current Ecosystem (CCE). The first mode reflected upwelling during the summer months and was characterized by low‐frequency (multidecadal) processes, including significant (P<0.01) linear trends at some latitudes. In contrast, the second mode reflected wintertime upwelling and was defined by higher‐frequency variability associated with the North Pacific High and El Niño Southern Oscillation events. These modes were compared with multidecadal time series of splitnose rockfish (Sebastes diploproa) otolith growth, yelloweye rockfish (S. ruberrimus) otolith growth, Chinook salmon (Oncorhynchus tshawytscha) scale growth, and indices of Cassin's auklet (Ptychoramphus aleuticus) and common murre (Uria aalge) reproduction in the central‐northern CCE. In redundancy and correlation analyses, salmon growth and Cassin's auklet fledgling success associated with the summer upwelling mode while all other time series associated with the winter upwelling mode, indicating that CCE biology was differentially sensitive to these seasonal upwelling patterns. Thus, upwelling occurred in unrelated seasonal modes with contrasting trends, atmospheric forcing mechanisms, and impacts on the biology of the CCE, underscoring the importance of seasonality when evaluating ecosystem response to climate variability and change.     

Impacts of passage migrant songbirds on behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala in Gibraltar

Explanations for the coexistence of migratory and sedentary (resident) birds are much debated: some authors have suggested that migrants make use of surplus resources not exploited by residents, whereas others have recorded ecological shifts in residents during periods when migrants are present. These shifts have been ascribed to the presence of migrants but could equally reflect seasonal variation in the distribution of resources required by sedentary species. Here we assess how the abundance of migrants affects the territorial behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala at a stop‐over site on the Rock of Gibraltar. There was a significant positive relationship between the abundance of migrants and the distances moved, time spent calling and the species and functional diversity of plants used by Sardinian Warblers on a daily basis, suggesting that migrants have a significant impact on residents.     

Assessing the sources and magnitude of diurnal nitrate variability in the San Joaquin River (California) with an in situ optical nitrate sensor and dual nitrate isotopes

1. We investigated diurnal nitrate (NO₃⁻) concentration variability in the San Joaquin River using an in situ optical NO₃⁻ sensor and discrete sampling during a 5‐day summer period characterized by high algal productivity. Dual NO₃⁻ isotopes (δ¹⁵N_NO3 and δ¹⁸O_NO3) and dissolved oxygen isotopes (δ¹⁸O_DO) were measured over 2 days to assess NO₃⁻ sources and biogeochemical controls over diurnal time‐scales. 2. Concerted temporal patterns of dissolved oxygen (DO) concentrations and δ¹⁸O_DO were consistent with photosynthesis, respiration and atmospheric O₂ exchange, providing evidence of diurnal biological processes independent of river discharge. 3. Surface water NO₃⁻ concentrations varied by up to 22% over a single diurnal cycle and up to 31% over the 5‐day study, but did not reveal concerted diurnal patterns at a frequency comparable to DO concentrations. The decoupling of δ¹⁵N_NO3 and δ¹⁸O_NO3 isotopes suggests that algal assimilation and denitrification are not major processes controlling diurnal NO₃⁻ variability in the San Joaquin River during the study. The lack of a clear explanation for NO₃⁻ variability likely reflects a combination of riverine biological processes and time‐varying physical transport of NO₃⁻ from upstream agricultural drains to the mainstem San Joaquin River. 4. The application of an in situ optical NO₃⁻ sensor along with discrete samples provides a view into the fine temporal structure of hydrochemical data and may allow for greater accuracy in pollution assessment.     

An information-theoretical approach to phylogeography

Data analysis in phylogeographic investigations is typically conducted in either a qualitative manner, or alternatively via the testing of null hypotheses. The former, where inferences about population processes are derived from geographical patterns of genetic variation, may be subject to confirmation bias and prone to overinterpretation. Testing the predictions of null hypotheses is arguably less prone to bias than qualitative approaches, but only if the tested hypotheses are biologically meaningful. As it is difficult to know a priori if this is the case, there is the general need for additional methodological approaches in phylogeographic research. Here, we explore an alternative method for analysing phylogeographic data that utilizes information theory to quantify the probability of multiple hypotheses given the data. We accomplish this by augmenting the model‐selection procedure implemented in ima with calculations of Akaike Information Criterion scores and model probabilities. We generate a ranking of 17 models each representing a set of historical evolutionary processes that may have contributed to the evolution of Plethodon idahoensis, and then quantify the relative strength of support for each hypothesis given the data using metrics borrowed from information theory. Our results suggest that two models have high probability given the data. Each of these models includes population divergence and estimates of ancestral θ that differ from estimates of descendent θ, inferences consistent with prior work in this system. However, the models disagree in that one includes migration as a parameter and one does not, suggesting that there are two regions of parameter space that produce model likelihoods that are similar in magnitude given our data. Results of a simulation study suggest that when data are simulated with migration, most of the optimal models include migration as a parameter, and further that when all of the shared polymorphism results from incomplete lineage sorting, most of the optimal models do not. The results could also indicate a lack of precision, which may be a product of the amount of data that we have collected. In any case, the information‐theoretic metrics that we have applied to the analysis of our data are statistically rigorous, as are hypothesis‐testing approaches, but move beyond the ‘reject/fail to reject’ dichotomy of conventional hypothesis testing in a manner that provides considerably more flexibility to researchers.     

Nest Turnover Rates and List-Frame Decay in Bald Eagles: Implications for the National Monitoring Plan

ABSTRACT In accordance with federal regulations, the United States Fish and Wildlife Service developed a postdelisting monitoring plan for the bald eagle (Haliaeetus leucocephalus) designed to detect a change in the number of occupied nests on a national scale. The plan employs a dual-frame approach to the survey design where a list frame (list of known nests) and an area frame (set of survey plots) are used in concert to estimate the number of occupied nests in 5-year intervals over a 20-year period. The plan offers no provisions for changes in list-frame integrity, nor does it contemplate the impact of such changes on survey performance. We used a long-term data set to quantify occupancy patterns for nests in Virginia, USA, and evaluated their influence on integrity of the list frame and performance of the proposed dual-frame monitoring approach. The average annual turnover rate for nests was 0.261, resulting in a rapid decay of the list frame. Decay of the list frame leads to a functional collapse of the dual-frame approach, down to the area-frame survey alone, early within the monitoring time horizon. This early decay of the list frame implies that the area-frame coverage needed to maintain the same statistical power as stated in the monitoring plan would have to be increased by a factor of 3 to 5 beyond that recommended in the current plan. Remedies for this deficiency undermine the cost benefit associated with inclusion of the list frame. We examined response of the dual-frame survey to variation in nest turnover rates and population growth rates and defined a state space where time to collapse is beyond the proposed 20-year time horizon. Because, under realistic estimates of turnover rates, the dual-frame approach collapses to the area frame within the proposed monitoring window, we recommend that the costs of list-frame maintenance be included in the procedure to optimize allocation of survey effort.