Uneven Rates of Landscape Change as a Source of Bias in Roadside Wildlife Surveys

ABSTRACT Roadside survey data have been used frequently to assess species occurrence and population trends and to establish conservation priorities. However, most studies using such data assume that samples are representative of either the amount of habitat or its rate of change at larger spatial scales. We tested both of these assumptions for the Breeding Bird Survey (BBS) from 1974 to 2001 in New Brunswick, Canada. Our study focused on mature forest—a cover type that we predicted would be characterized by rapid change due to human activities and that is of high ecological importance. We also sought to determine whether land cover changes adjacent to BBS routes were related to bird population trends detected in BBS data. Within all 3 time periods examined (1970s, 1980s, and 1990s), the amount of mature forest adjacent to BBS routes was significantly lower than in surrounding 1° blocks of latitude and longitude. This could be problematic for studies that use roadside data to compare the relative abundance of species. On average, mature forest declined at a rate of-1.5% per year over the 28-year study period. We detected no significant difference in the rate of change between degree blocks and BBS routes over this time span. However, in the 1970s and 1980s, mature forest declined more rapidly in degree blocks (-2.7%/yr) than adjacent to BBS routes (-0.5/yr). We also found that the BBS trend for a mature forest-associated species, blackburnian warbler (Dendroica fusca), was correlated with the trend in mature forest along BBS routes. This, combined with slower rates of mature forest change along routes in the 1970s and 1980s, suggests that BBS data may have underestimated population declines during this period. It is important that research be conducted to test for potential biases in roadside surveys caused by uneven rates of landscape change, particularly in regions characterized by rapid habitat alteration.     

Wave-induced shear stresses, plant nutrients and chlorophyll in seven shallow lakes

1. Sediment resuspension dynamics were investigated in relation to changes in water column nutrients (TP, TN, PO₄-P, NO₃-N and NH₄-N), chlorophyll a and phaeopigment in seven shallow ( Z _m < 1.5 m) lakes in South Island, New Zealand, ranging in area from 0.1 to 180 km².
2. Benthic shear stress, calculated from wind speed, effective fetch and depth, was a considerably better predictor of nutrient and pigment concentrations than wind speed.
3. For TP, TN, chlorophyll a and phaeopigment, sixteen of the possible twenty-eight linear correlations with benthic shear stress were significant at P < 0.05, with 16–87% of the variation being explained by shear stress.
4. Wind decreased the ratios of TN : TP, with ratios exponentially approaching those of the sediments as shear stress increased in four of the lakes.
5. Relationships of dissolved inorganic nutrients to shear stress were considerably weaker than those for total nutrients and showed no consistent trend over the seven lakes.
6. Estimated annual mean TP inclusive of resuspension was over four times higher than that derived from measured calm samples in two lakes.
7. The number of nutrient and pigment parameters that were significantly correlated with shear stress and the strengths of the relationships varied widely from lake to lake. We could establish no simple relationships between these effects and any single characteristic of the lake, sediment, or water.
8. A function is developed to predict the rate of entrainment of TN and TP in response to an applied shear stress, where the independent variables are sediment nutrient content and particle size, and the macrophyte density in the lake.     

Infectibility of some new raspberry cultivars with arabismosaic and raspberry ringspot viruses and further evidence for variation in British isolates of these two nepoviruses

In field trials at sites of an outbreak of arabis mosaic nepovirus (AMV) in England and of raspberry ringspot nepovirus (RRV) in Scotland, the results of exposure of some new raspberry cultivars to natural infection with these viruses showed discrepancies from those obtained in graft inoculation tests using AMV-Lib and RRV-S, the Scottish type isolates. In particular, cv. Glen Prosen, which is immune to AMV-Lib and RRV-S, was infected with AMV and RRV in the field trials. Studies on these and other field isolates of AMV and RRV showed that they differed from the type isolates in Rubus host range and in symptomatology in herbaceous hosts. However, whereas four isolates of RRV found infecting Rubus were distinguishable by spur formation in gel double-diffusion serological tests, six AMV isolates were indistinguishable by this method. Immunoelectrophoresis of virus particles did not distinguish the six AMV isolates, but isolates RRV-MX and RRV-T were distinguishable from RRV-S and the English type isolate, RRV-E. Like the two RRV type isolates, RRV-MX contained a single electrophoretic component, but it migrated must faster whereas RRV-T contained two components, one with a migration rate similar to that of RRV-MX and the other similar to that of the type isolates. Polyacrylamide gel electrophoresis of protein preparations from highly purified virus particles of RRV isolates E, S and MX detected a single polypeptide of estimated mol. wt 54 × 10³, 54 × 10³ and 50 × 10³ respectively but that of isolate T contained two polypeptides of estimated mol. wt 54 × 10³ and 50 × 10³. These data suggest that RRV-T is a mixture of two isolates. In laboratory tests the nematode Xiphinema diversicaudatum transmitted four isolates of AMV efficiently whereas two populations of the nematode Longidorus elongatus were less efficient vectors of four RRV isolates. Neither vector species transmitted virus to any of nine raspberry cultivars. The results are discussed in relation to the control of nepoviruses in raspberry and to the biology of these viruses.     

Geographic and stratigraphic change in the morphology of Triarthrus beckii (Green) (Trilobita): a test of the Plus ça change model of evolution

The Plus ça change model predicts that deepwater trilobite species such as Triarthrus should exhibit gradual phyletic evolution. A detailed stratigraphic sequence of Triarthrus beckii specimens considered together with geographically separated samples from a single time interval provide a test of the Plus ça change model. We examined geographic patterns of variation in cranidial shape based on specimens from four approximately synchronous levels within the Upper Ordovician (lower Edenian) strata of New York, Québec, Kentucky and Pennsylvania. All geographic populations differ in mean size, except for New York and Pennsylvania. Because allometry is present in both meraspid and holaspid phases of the trilobite, size effects on shape were removed by ontogenetic standardization. Cranidial shapes were then compared among the four study sites and eight stratophenetic samples from New York, obtained by subdividing our Mohawkian Composite Standard Section into 20-m-thick intervals. Goodall's F-test of pairwise comparisons of cranidial shape between eight subintervals in New York and the other three populations are all significant. Geographic variation in cranidial size and shape in T . beckii appears to display a gradient or cline-like pattern that is related to paleogeography. Although cranidial shape is not entirely static within the New York stratophenetic series, it is in all cases different from that sampled elsewhere in the region. Thus, there is no evidence of wholesale immigration and emigration among the geographic areas. Instead, the geographic gradient of T . beckii shape variation may have remained fairly stable over ca. 3 million years during the mid-Chatfieldian to early Edenian interval. This result is indicative of stasis. Consequently, the evolutionary history of T . beckii contradicts the Plus ça change model.     

A marking device for the identification and measurement of growth zones in seedlings with minimum mechanical stress1

A device was designed to mark the growth zones of elongating seedling stems rapidly and accurately without exposing the tissue to mechanical stress. The device consists of a spring-loaded clamp, two plastic, grooved holders attached to either side of the open end of the clamp, a narrow foam pad to cushion and support the plant tissue, and a narrow nylon marking head. The marking head contains flat-topped ridges, 0·5 mm in width, machined such that the ridges are 2 mm (± 0·1) apart. Marking is accomplished using India ink. The procedure is rapid, precise, relatively inexpensive to build and operate, and does not require sophisticated or expensive instrumentation to obtain meaningful data. With practice, up to 100 seedlings may be uniformly marked in one hour. Tests using dark-grown soybean (Glycine max), sunflower (Helianthus annuus), and pea (Pisum sativum) show that the device does not itself cause a reduction in growth.