Predation and caribou populations

Predation, especially wolf (Canis lupus) predation, limits many North American caribou (Rangifer tarandus) populations below the density that food resources could sustain. The impact of predation depends on the parameters for the functional and numerical response of the wolves, relative to the potential annual increment of the caribou population. Differences in predator-avoidance strategies largely explain the major differences in caribou densities that occur naturally in North America. Caribou migrations that spatially separate caribou from wolves allow relatively high densities of caribou to survive. Non-migratory caribou that live in areas where wolf populations are sustained by alternate prey can be eliminated by wolf predation

Ecosystem management and the conservation of caribou habitat in British Columbia

Woodland caribou (Rangifer tarandus caribou) in British Columbia inhabit a wide variety of forest ecosystems. Numerous research projects have provided information that has been used to develop caribou habitat management recommendations for different areas. Recently, the province has implemented guidelines to protect biodiversity that are based on an ecosystem management strategy of mimicking natural forest conditions. There is a great deal of similarity between caribou management recommendations and biodiversity recommendations within different forest types. In mountain caribou habitat, both approaches recommend maintaining a landscape dominated by old and mature forests, uneven-aged management, small cutblocks, and maintaining mature forest connectivity. In northern caribou habitat, both approaches recommend maintaining some older stands on the landscape (but less than for mountain caribou), even-aged management, and a mosaic of large harvest units and leave areas. The ecosystem management recommendations provide a useful foundation for caribou habitat conservation. More detailed information on caribou and other management objectives can then be used to fine-tune those recommendations

Reconstruction of Bandlimited Functions from Unsigned Samples

We consider the recovery of real-valued bandlimited functions from the absolute values of their samples, possibly spaced nonuniformly. We show that such a reconstruction is always possible if the function is sampled at more than twice its Nyquist rate, and may not necessarily be possible if the samples are taken at less than twice the Nyquist rate. In the case of uniform samples, we also describe an FFT-based algorithm to perform the reconstruction. We prove that it converges exponentially rapidly in the number of samples used and examine its numerical behavior on some test cases

Inventarisatie van macrozoobenthos in de Voordelta: dichtheden voor de najaarstocht van 1984 en de voorjaarstocht van 1985

In the frame of the Fore-Delta-research (see introduction and fig. 1) a soil animal inventarisation has been done. Three trips were made: fall 1984, spring 1985(1985-1) and fall 1985 (1985-2). In this report the densities of the first and the second trip are discussed. In the (sublittoral) research area, that has a surface of ca. 1200 km², 125 species were found, which are mentioned in table 1.The 14 most general species (vgl. Tables 16 and 27) are: -the chaetopods <i>Scoloplos armiger, Nephtys hombergii, Nephtys cirrosa, Magelona papillicornis, Spiophanes bombyx, Spio filicornis</i> and <i>Capitella capitata</i>; -the freshwater shrimp <i>Bathyporeia elegans</i> and <i>Urothoe poseidonis</i>; -the bivalves <i>Spisula subtruncata, Tellina fabula</i> and <i>Macoma balthica</i>; -the sea star <i>Ophiura texturata</i> and -the Nemertinea group). The approach is summarised in figure 2: the strategy of sample taking was adjusted to the results of the previous trip.By TWINSPAN-classification of density data of 1984 it showed a special pattern could be distinguished, as far as soil animal composition and densities were concerned, on two similar stations. This made a strata-classification (6 strata) based on soil animal data possible. At the start of the project this was not yet possible based on available soil or soil animal data. At the second trip, a “stratified random” sampling was then done to be able to estimate accurately the densities per stratum. Reliability intervals for the geometric average density are calculated. The data are log-transformed, then the average of the observations is determined and this value is then transformed back for the individual strata and for the entire area (see table 27, figures 29-35 and the figures of appendix 4a). A strong correlation between the geometric average density and the frequency of the species was found (see 4 and 6). During the comparison of the TWINSPAN-classification of the data of the first two BOVO-trips, similar special patterns were discovered, stable zonation be it (see figures 25-28). The strata classification, deduced from the second trip and used for the third, is refined (10 strata), compared to the previous strata classification (6 strata) based on the first trip (see overlays 1 and 2). The northern strata (fine sand with low-average mud content) are relatively rich in species and individuals per sample (see figures 52 and 53). The Wester Scheldt mouth (with a high mud content in the mainly fine sand soils and the highly suppressive dust content in the water column) and parts of the Easter Scheldt mouth (where, in accordance to the high speed of streams, low mud contents are found in the middle grove sandy soil) showed few species and individuals per sample in 1984-1985 (see figures 23 and 24). Per stratum an abiotic description is given (see 3 and table 9). Per species correlations were sought in a graphic way with measured soil factors and the depth, and the ecologic distribution was researched, based on data from the second trip (see 5 and e.g. the figures 38, 41 and 45). On the entire density-dataset (1984 and 1985-1 apart) an ordination (DECORANA) technique has been applied, and more research for order-correlation with measured soil factors and the depth (see 2.5). These proved to be statistically significant correlated with one or more of the DECORANA-ordination-axes (see 5). Extremely high correlations were found with the mud content (and the group of correlated variables) (see table 26 and fig. 49). In relation to the application of different techniques for sample taking (Reineck-box corer and Van Veen-grab), these have been compared to each other on penetration-depth and density estimations for soil animals (see 2). The Box-Corer penetrated (mean 26 cm) noticeably deeper than the Van Veen-grab (mean 15 cm) (see table 4 en figures 3a en 3b). Only for the polychaetes <i>Magelona papillicornis</i> and <i>Nephtys cirrosa</i> and for the amphipode <i>Urothoe poseidonis</i> the density (p< 0.05) was significantly higher in the box. This also counts for the total density of all species, for the polychaetes and for the Amphipoda (cfr. table 5). In the discussion (see 6) a.o. a comparison is considered with data from Wolff from the period 1958-1969. From this we can conclude that sea species such as <i>Tellina fabula</i> have become more common in the Fore Delta. In the report a selection of the most remarkable figures is presented ; the others can be found in some appendix. (These can be consulted at the library of the NIOZ in Texel and at RWS-DGW in Middelburg)

Introduction to the Population Ecology of North American Caribou

Bergerud has discussed how major differences in caribou density across North America appear to be related to the impact of wolf (Canis lupus) predation, and the strategies used by caribou to avoid wolves. Caribou living in areas without wolves usually occur at high densities and are regulated by competition for food. In this session, we asked the presenters to discuss the population ecology of different caribou herds in North America and to evaluate if they fit the general model

MOUNTAIN CARIBOU INTERACTIONS WITH WOLVES AND MOOSE IN CENTRAL BRITISH COLUMBIA

Mountain caribou (Rangifer tarandus caribou) populations in south-eastern British Columbia are declining over most of their range and are listed as Threatened. Predation has been documented as the major cause of declining caribou numbers. Excessive predation by wolves (Canis lupus) has been related to increased moose (Alces alces) numbers. The increase in moose appears to be the result of a natural colonization process that has been enhanced by human-caused habitat change. Options to reduce the rate of predation include reducing wolves, reducing moose, and reducing the amount of early seral habitat that supports moose. Current management includes population control of moose and wolves. Monitoring and assessment of these approaches will guide the future management strategy used to maintain mountain caribou in south-eastern British Columbia

Comparison of seasonal habitat selection between threatened woodland caribou ecotypes in central British Columbia

Woodland caribou (Rangifer tarandus caribou) in British Columbia have been classified into ecotypes based on differences in use of habitat in winter. Although recovery planning focuses on ecotypes, habitat use and selection varies within ecotypes. Our objectives were to compare habitat use and selection among previously identified woodland caribou herds at the transition zone between northern (Moberly, Quintette, and Kennedy herds) and mountain (Parsnip herd) ecotypes in central British Columbia. We developed selection models for each herd in spring, calving, summer/fall, early and late winter. Topographic models best predicted selection by most herds in most seasons, but importance of vegetation-cover was highlighted by disproportionate use of specific vegetation-cover types by all caribou herds (e.g., in early winter, 75% of Kennedy locations were in pine-leading stands, 84% of Parsnip locations were in fir and fir-leading stands, and 87 and 96% of locations were in alpine for the Moberly and Quintette herds, respectively). Using a combination of GPS and VHF radio-collar locations, we documented some spatial overlap among herds within the year, but use of vegetation-cover types and selection of elevations, aspects, and vegetation-cover types differed among herds and within ecotypes in all seasons. Habitat use and selection were most similar between the two northern-ecotype herds residing on the eastern side of the Rocky Mountains. This research indicates that habitat use and selection by caribou herds in all seasons is more variable than ecotype classifications suggest and demonstrates the value of undertaking herd-specific mapping of critical habitat for woodland caribou