Eric Archer

When are genetic methods useful for estimating contemporary abundance and detecting population trends

The utility of microsatellite markers for inferring population size and trend has not been rigorously examined, even though these markers are commonly used to monitor the demography of natural populations. We assessed the ability of a linkage disequilibrium estimator of effective population size (Ne) and a simple capture‐recapture estimator of abundance (N) to quantify the size and trend of stable or declining populations (true N = 100–10,000), using simulated Wright–Fisher populations. Neither method accurately or precisely estimated abundance at sample sizes of S = 30 individuals, regardless of true N. However, if larger samples of S = 60 or 120 individuals were collected, these methods provided useful insights into abundance and trends for populations of N = 100–500. At small population sizes (N = 100 or 250), precision of the Ne estimates was improved slightly more by a doubling of loci sampled than by a doubling of individuals sampled. In general, monitoring Ne proved a more robust means of identifying stable and declining populations than monitoring N over most of the parameter space we explored, and performance of the Ne estimator is further enhanced if the Ne/N ratio is low. However, at the largest population size (N = 10,000), N estimation outperformed Ne. Both methods generally required ≥ 5 generations to pass between sampling events to correctly identify population trend.

An Analysis of Stream Habitat Conditions in Reference and Managed Watersheds on Some Federal Lands within the Columbia River Basin

Abstract The loss of both habitat quality and quantity for anadromous fish in the Columbia River basin has been identified as a major factor in the decline of many species and has been linked to a variety of land management activities. In this study, we compared stream reaches in watersheds representing both managed and reference conditions to determine whether we could detect differences in physical habitat variables. We divided stream habitat measures into three components: Stream banks, instream habitat (pools and pool depth), and stream substrate. We randomly sampled perennial streams within 261 sixth hydrologic unit code (HUC) stream reaches on federal lands in Idaho, Montana, Oregon, and Washington. The sample population represented stream reaches in 62 reference watersheds and 199 managed watersheds. An unbalanced, incomplete-block-design analysis of covariance (ANCOVA) was performed on each of the habitat variables using geology type as the block effect and bank-full width, stream gradient, and av...

Quantifying the Extent of and Factors Associated with the Temporal Variability of Physical Stream Habitat in Headwater Streams in the Interior Columbia River Basin

Abstract The quality and quantity of stream habitat can have profound impacts on the distribution and abundance of aquatic species. Stream networks, however, are dynamic in their response to natural- and human-induced disturbance regimes, which results in spatially explicit patterns of temporal variability. Quantifying spatial patterns in habitat (temporal) variability across different sites and identifying those factors associated with different levels of variability are important steps for stream habitat assessments. We evaluated the temporal variability in stream habitat over a 9-year period for 47headwater streams of the interior Columbia River basin. We used repeat-measures analyses to calculate temporal variability as root mean square error for six habitat attributes at each site. Multiple linear regression analyses with root mean square error as the response were then used to quantify which landscape, climate, and disturbance attributes were associated with different levels of temporal variability ...

Evaluating Livestock Grazing Use With Streambank Alteration Protocols: Challenges and Solutions

Abstract Appropriate management of livestock in riparian areas can help ensure that these ecosystems are maintained. We evaluated how one indicator of livestock grazing in riparian areas, streambank alteration, was affected by choices related to protocols and personnel used for these assessments. We found that although streambank alteration protocols were generally repeatable among observers, results were affected by factors not directly related to grazing intensity, including 1) training, 2) professional background, 3) location and intensity of measurements, and 4) the protocol used. Training reduced estimates of alteration and observer variability. Rangeland professionals had higher estimates of streambank alteration than seasonal technicians. Rapid assessments of alteration were correlated with more intensive estimates; however, the relationship was not 1∶1. Different protocols resulted in different alterations estimates when alterations at the same locations were estimated. Given the large number of monitoring programs, personnel, and methods used to assess streambank alteration, we suggest more thought be given on how to standardize monitoring efforts so results consistently reflect the true amount of alteration at a site. We also remind managers that no protocol can be implemented without some error. Managers should therefore be careful when taking action based on a single evaluation—especially when the result is near a management standard or threshold. When these concerns are addressed, indicators such as streambank alteration can help ensure management decisions maintain both sustainable allotments and landscapes.