Nams, V.O. (submitted). Shape of patch edges affects edge permeability.
Abstract
Human development typically fragments natural habitats into patches, affecting population and metapopulation dynamics via changes in animal behaviour. Emigration from one habitat patch to another has a large effect on metapopulation dynamics. One factor that affects emigration is permeability of patch edges. This study looks at the effects of edge shape (convex, concave and straight) on edge permeability for meadow voles (Microtus pennsylvanicus). I tested 5 hypotheses for responses of animal movement to patch shape: (i) neutral edge response, (ii) edge-attraction, (iii) edge-avoidance (iv) time-minimizing: a dispersing animal attempts to minimize the time spent in inhospitable matrix, and thus travels as far as possible in the patch before crossing the edge, and (v) protection: an animal attempts to maximize protection while in the inhospitable matrix by keeping the patch close by. These hypotheses were tested by an experimental manipulation of meadow vole habitats. A strip was mowed with different edge shapes through an old field and vole response was measured by tracking plates. Voles crossed edges at concave treatments twice as much as compared to convex and straight. Hypotheses (ii) and (v) were accepted. While edge-attraction causes a passive effect of a decrease in edge-crossing at concavities, this was eclipsed by the active effect of voles choosing to cross at concavities. The results can be generalized to edge tortuousity in general. Conservation biologists should consider edge shapes when exploring the effects of habitat fragmentation on animal populations.
Nams, V.O. (in press). Emergent properties of patch shapes affect edge permeability to animals. PloS ONE
Abstract
Animal travel between habitat patches affects populations, communities and ecosystems. There are three levels of organization of edge properties, and each of these can affect animals. At the lowest level are the different habitats on each side of an edge, then there is the edge itself, and finally, at the highest level of organization, is the geometry or structure of the edge. This study used computer simulations to: 1) find out whether effects of edge shapes on animal behavior can arise as emergent properties solely due to reactions to edges in general, without the animals reacting to the shapes of the edges, and to 2) generate predictions to allow field and experimental studies to test mechanisms of edge shape response. Individual animals were modeled traveling inside a habitat patch that had different kinds of edge shapes (convex, concave and straight). When animals responded edges of patches, this created an emergent property of responding to the shape of the edge. The response was mostly to absolute width of the shapes, and not the narrowness of them. When animals were attracted to edges, then they tended to collect in convexities and disperse from concavities, and the opposite happened when animals avoided edges. Most of the responses occurred within a distance of 40% of the perceptual range from the tip of the shapes. Predictions were produced for directionality at various locations and combinations of treatments, to be used for testing edge behavior mechanisms. These results suggest that edge shapes tend to either concentrate or disperse animals, simply because the animals are either attracted to or avoid edges, with an effect as great as 3 times the normal density. Thus edge shape could affect processes like pollination, seed predation and dispersal and predator abundance.
Kennedy, K. J., Boyd, N.S., Nams, V.O. and Olson, A. R. (2011). The impacts of fertilizer and hexazinone on sheep sorrel growth patterns in lowbush blueberry fields. Weed Science. 59(3): 335-340.
Abstract
Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields that decreases yields and hinders harvest. Much of the basic phenology of sheep sorrel in blueberry fields is unknown and not documented in peer-reviewed journals. Three levels of fertilizer (0, 20, and 40 kg N ha−1) and two levels of hexazinone (0 and 1.92 kg ai ha−1) were applied to three vegetative-year blueberry fields to determine their effects on root and shoot growth, biomass allocation, and seed production of sheep sorrel plants. Hexazinone efficacy varied widely between sites, but suppressed shoot biomass, achene number and weight, and reproductive biomass, as well as the reproductive:shoot biomass ratio. Fertilizer tended to increase achene number and increased sheep sorrel shoot biomass in the absence of hexazinone, but had no effect on achene weight, root biomass, or reproductive biomass. When fertilizer was applied, sheep sorrel allocated resources to sexual reproduction at the expense of vegetative growth.
Kearns, W. D., Fozard, J. L. and Nams, V.O. (2011). Wireless telesurveillance system for detecting dementia. Gerontology. 10:90-102.
Abstract
Objective We hypothesized path tortuosity (an index of casual locomotor variability) measured by a movement telesurveillance system would be greater for assisted living facility residents clinically diagnosed with dementia. Background We examined the relationship of dementia to path tortuosity and to movement speed and path length variability, both of which increase in dementia. Methods Daytime movements of 25 elders (19 female; 14 with dementia; average age 80.6) were monitored for 30 days using radio transponders measuring location to 20 cm. After 30 days, the Mini Mental State Exam (MMSE) and Revised Algase Wandering Scale-Community Version (RAWS-CV) were administered. Results Fractal Dimension (Fractal D), a measure of path tortuosity, correctly classified all but 2 residents with dementia; sensitivity 0.857, specificity 0.818 while the MMSE had 6 misclassifications, a sensitivity of 0.857 and a specificity of 0.727. Individual logistic regressions of dementia diagnosis on predictors MMSE and Fractal D were significant, but a logistic regression using both predictors found Fractal D marginal- ly predictive of dementia (p=0.055) while the MMSE was not (p=0.168). Although significantly correlated with Fractal D, rate of travel and mean path distance were not predictive of dementia. Fractal D correlated negatively with overall MMSE (r= -0.44, n=25, p<0.05) but the relationship was mediated by MMSE Geographical Orientation items. Fractal D was unrelated to the RAWS-CV. Conclusions Telesur- veillance-measured path tortuosity is greater in persons diagnosed with dementia. Persons with dementia have relatively more impaired spatial memory which is required for successful navigation. Application Automatic monitoring of direction, length and speed of unconstrained movements.
Kennedy, K. J., Boyd, N. S., and V. O. Nams. (2010). Hexazinone and nitrogen rate impacts on sheep sorrel (Rumex acetosella L.) in wild blueberry. Weed Science. 58:317-322. Abstract. Complete paper, pdf.
Abstract
Sheep sorrel is an invasive, creeping perennial weed of lowbush blueberry fields. It is one of the most prominent weeds in blueberry fields in Nova Scotia and is responsible for decreasing yields. Three levels of fertilizer (0, 20, 40 kg N ha−1) and two levels of hexazinone (0 or 1.92 kg ai ha−1) were applied to experimental plots to determine their effects on sheep sorrel density. Sprout-year hexazinone reduced sheep sorrel densities, which led to increased yields. Fertilizer increased weed density in the absence of herbicides, had no effect on density in the presence of herbicides, tended to have no impact on floral buds, and did not increase yields. Fruiting-year hexazinone decreased sheep sorrel densities in some situations, but did not result in yield increases.
Kearns, W.D., Nams, V.O., and Fozard, J.L. (2010). Wireless fractal estimation of tortuosity in movement paths related to cognitive impairment in assisted living facility residents. Methods of Information in Medicine. 49
Abstract
Background: Using traditional assessment procedures, prior research demonstrated that deficiencies in gait and balance occur in the later stages of dementia. Objective: We tested the hypothesis that an automated system capable of detecting path tortuosity (aimless movement) in elders would show that greater tortuosity was associated with greater cognitive impairment, potentially allowing early detection of dementia over time as tortuosity levels slowly increased. Methods: An Ultra Wideband sensor network using wireless transponders measured daytime locomotion to an accuracy of 20cm in 14 elderly residents in an assisted living facility (ALF) as they traversed a shared living area while performing daily activities such as going to a dining area, conversing and watching television. Transponder location was updated at 0.4 sec intervals while in motion and revealed large individual differences in activity patterns. Results: Fractal Dimension (Fractal D), a measure of movement path tortuosity (directed vs. aimless locomotion) was significantly and negatively correlated with cognitive status as measured by the Mini Mental State Examination administered to each participant at the study’s end. Conclusions: Previous studies of locomotion in laboratory settings that have demonstrated gait variability increases with poor cognitive status have necessarily controlled various components of gait. The present results demonstrate that directional changes and other locomotion components can be studied by monitoring free movements in normal living settings over time. Implications for assessment and management of dementia-related wandering are discussed.
Delgado, M.D., Penteriani, V., Revilla, E. and Nams, V.O. (in press) The effect of phenotypic traits and external cues on natal dispersal movements. Journal of Animal Ecology.
Abstract
1. Natal dispersal has the potential to affect most
ecological and evolutionary processes. However, despite its importance, this
complex ecological process still represents a significant gap in our understanding
of animal ecology due to both the lack of empirical data and the intrinsic
complexity of dispersal dynamics.
2. By studying natal dispersal of 74 radiotagged juvenile eagle owls Bubo
bubo, in both the wandering and the settlement phases, we empirically
addressed the complex interactions by which individual phenotypic traits and
external cues jointly shape individual heterogeneity through the different
phases of dispersal, both at nightly and weekly temporal scales.
3. The high complexity and heterogeneity of the dispersal patterns that we
observe results from the non-exclusive combination of many internal and
external factors and constraints, which continuously recombine in a highly
dynamic cascading sequence. More precisely, when studying dispersal, we are
faced with a three-stage process (i.e. departure, transience or wandering,
and settlement or stop) during which the internal state of
dispersers and external factors interact. It is crucial to take into account
that the mechanisms linking external factors and phenotypic traits can vary
between these phases, and that decisions taken at one stage may influence behavioural
choices of the next stage.
4. The combination of the information coming from the relationships among a
large set of factors acting and integrating at different spatial and temporal
scales, under the perspective of heterogeneous life-histories, are a fruitful
ground for future understanding of natal dispersal.
Delgado, M.D., Penteriani, V., Nams, V.O. and Campioni, L. (2009). Changes of movement patterns from early dispersal to settlement. Behavioral Ecology and Sociobiology. 64:35-43.
Abstract
Moving and spatial learning are two intertwined processes: (a) changes in movement behavior determine the learning of the spatial environment, and (b) information plays a crucial role in several animal decision-making processes like movement decisions. A useful way to explore the interactions between movement decisions and learning of the spatial environment is by comparing individual behaviors during the different phases of natal dispersal (when individuals move across more or less unknown habitats) with movements and choices of breeders (who repeatedly move within fixed home ranges), that is, by comparing behaviors between individuals who are still acquiring information vs. individuals with a more complete knowledge of their surroundings. When analyzing movement patterns of eagle owls, Bubo bubo, belonging to three status classes (floaters wandering across unknown environments, floaters already settled in temporary settlement areas, and territory owners with a well-established home range), we found that: (1) wandering individuals move faster than when established in a more stable or fixed settlement area, traveling larger and straighter paths with longer move steps; and (2) when floaters settle in a permanent area, then they show movement behavior similar to territory owners. Thus, movement patterns show a transition from exploratory strategies, when animals have incomplete environmental information, to a more familiar way to exploit their activity areas as they get to know the environment better.
Nams, V.O. (submitted). Effects of discretizing correlated random walks.
Abstract
Animal movement models allow ecologists to study processes that operate over a wide range of scales - from local to landscape. Correlated random walk (CRW) models have been used both to model and to explore the biological mechanisms of movement. In a CRW an animal makes discrete steps, and at each step the turning angle is independent of the previous turning angle. Often the sampled path is gathered at a different scale than that of the animals' discrete steps; this is termed 'discretization'. This paper uses simulated CRWs and shows that discretizing CRWs causes smaller turning angles and creates correlations between successive turning angles. The only way to sample a movement path that is not discretized is by using natural end-points for the steps and by sampling them at the correct spatial scale, but without using natural end-points there is no known way to find the correct spatial scale. The discretization also biases statistical tests for CRWs and causes an overestimate in distances travelled; a correction is given for these biases. The discretization effect suggests that there is a natural scale to CRWs - that if CRWs are viewed at other spatial scales then they are no longer CRWs. On the other hand, while there is a natural scale to CRWs, distance-discretizated CRWs are in a sense, scale invariant. Authors need to be aware of the biases caused by discretizing correlated random walks, and deal with them appropriately.
Delgado, M.D., Penteriani, V., and Nams, V. O. (2009) How fledglings explore surroundings from fledging to dispersal. A case study with Eagle Owls Bubo bubo. Ardea. 97 (1): 7-15
Abstract
Movement strategies are one of the primary mechanisms underlying animal survival. Despite the impressive amount of studies on animal movement during successive stages in the life history of birds, little is known about the characteristics of movements during the post-fledging dependence period. Such a period represents a crucial phase of the life history during which individuals can show important displacements around the natal nest. Here we present path search strategies employed by radio-tagged fledgling Eagle Owls Bubo bubo during the post-fledging dependence period (1962 locations from 41 tagged owlets). During the post-fledging dependence period, individuals show dynamic movement behaviours that might be related to the development of individuals' mobility and cognitive abilities. Immediately after leaving the nest, individuals focused their activities close to the nest, but after a few weeks individuals travelled further and faster, up to the moment that they started to disperse. At the time that the mobility of owlets was highest, their movements described straighter paths. Movement patterns were not affected by morphological- or physiological parameters of body condition. Between-sibling distances showed a significant interaction between sex and time: until 20 days after owlets left the nest, siblings were closer together, independently of the sex. Between-sibling distances increased with time as individuals became increasingly mobile; just before the start of dispersal, family units seemed to dissolve.
V. O. Nams and R. J. Martin (2007). The effects of turnout date on cattle weight gain. Can. J. Animal Science 87:527-534
Abstract
The effects of multiple turnout dates on cattle weight gain was assessed in Nova Scotia, Canada, in 1999 and 2000. Steers and heifers were released into pasture every second day from May 6 to May 26 in 1999 and April 26 to June 5 in 2000. All cattle were weighed just before turnout and periodically while on pasture. Cattle turned out to pasture later in the season, gained less weight. Turnout date had a similar effect in both years, and one day of earlier turnout increased weight by 0.789 kg per animal over the summer; however cattle overall gained more weight in 2000 than in 1999. The length of recovery period (the time for cattle weight to recover after entering the pasture) did not vary with turnout date, but it did differ significantly between years, with cattle recovering weight faster in 2000 than in 1999. There was no significant interaction between turnout date and year. Rate of weight gain decreased throughout the summer. The results suggest a mechanism for the turnout date effect: that cattle grow fastest on the pasture at the start of the season, and they grow faster on the pasture than in the barn. Thus the earlier that they are introduced into the pasture, the more time they spend in the pasture during peak weight gain time. Rotational grazing maximizes the effect of turnout date by minimizing potential pasture degradation caused by early turnout. Thus, early turnout should offer economic benefits to cattle producers in the Atlantic Provinces.
Eaton, L. J. and V. O. Nams (2006). Second cropping of wild blueberries - effects of management practices. Canadian Journal of Plant Science. 86:1189-1195
Abstract
Wild blueberries (Vaccinium angustifolium Ait.) are normally managed on a biennial basis. Pruning forces the plant into a vegetative year without fruit, followed by the first crop year, which provides the greatest harvest. In subsequent years, harvest levels drop dramatically. Prior to the introduction of selective herbicides, second crop yields were too low to allow the adoption of a double harvest. This study was initiated to compare production and incomes of a single cropping (the present system) versus a double cropping system, using management systems that include herbicides. Total yields and net incomes over the 12 year study were affected by fertilizer applications, but not by management system (2 year, single crop versus 3 year, double crop) or pruning (burning versus mowing). Yields in second-crop plots were lower than those in first-crop plots, even though blossom numbers were higher. Fertilizer affected many aspects of blueberry plant development, including stem length, numbers of buds and blossoms, and fruit yields. Over time, second crop yields and net incomes were similar to those for the standard single crop system.
Nams, V. O. (2006). Detecting oriented movement of animals. Animal Behaviour. 72: 1197-1203
Abstract
A new test, called the Scaling test for directed movement, to differentiate between oriented and random movement paths is presented. It is based on testing whether movement paths approximate correlated random walks (CRW), when sampled at larger spatial scales. When sampled at larger scales, oriented paths travel significantly further than CRW while random paths travel either similar distances or significantly shorter distances. The Scaling test was tested using 3 models of random movement and 3 models of oriented movement, as well as applied to field data from small mammals. One surprising result is that when CRW are sampled at larger spatial scales the paths no longer follow CRW. The Scaling test assumes spatial and scalar heterogeneity in the movement path.
Caldwell, I., and Nams, V. O. (2006). A compass without a map: Tortuosity and orientation of eastern painted turtles (Chrysemys picta picta) released in unfamiliar territory. Canadian Journal of Zoology 84(8): 1129–1137
Abstract
All turtles must journey on land for parts of their life cycle. To make these journeys as short as possible, turtles have evolved mechanisms to locate and navigate towards nearby bodies of water. It is not known at which distance they detect water, and whether there is a mechanism for water finding in general or if there are separate mechanisms for familiar and unfamiliar areas. This study tested whether eastern painted turtles can locate and navigate towards unfamiliar water at five release distances. To accomplish this, the effect of distance from an unfamiliar lake on both orientation and tortuosity of turtle trails was determined. Sixty turtles were released at one of twenty release points located at five distances from two lakes. Using thread packets and a GPS unit, coordinates were collected then analyzed using a V-test for orientation and fractal dimension for tortuosity. Turtles did not orient in a waterward direction from any distance, but their trails were quitestraight. Turtles could maintain direction after their initial choice, but either could not detect water or were not motivated to reach it. Results support the hypothesis of a compass mechanism for finding water in both familiar and unfamiliar areas. In familiar areas a map could be used with the compass to locate water quickly, while in unfamiliar areas a compass mechanism can maintain direction, but without a map the initial choice of direction is random.
Nams, V. O. (2006). Improving accuracy and precision in estimating fractal dimension of animal movement paths. Acta Biotheoretica 54:1-11
Abstract
It is difficult to watch wild animals while they move, so often biologists analyze characteristics of animal movement paths. One common path characteristic used is tortuousity, measured using the fractal dimension (D). The typical method for estimating fractal D, the divider method, is biased and imprecise. The bias occurs because the path length is truncated. I present a method for estimating the truncation error. The imprecision occurs because sometimes the divider steps land inside the bends of curves, and sometimes they do not. I present three methods for minimizing this variation. I test all methods with simulated correlated random walks. The traditional divider method significantly overestimates fractal D when paths are short and the range of spatial scales is narrow. The best method to overcome these problems consists of walking the dividers forwards and backwards along the path, and then estimating the path length remaining at the end of the last divider step.
Nams, V. O (2005). Using animal movement paths to measure response to spatial scale. Oecologia 143:179-188.
Abstract:
Animals live in an environment that is patchy and hierarchical. I present a method of detecting the scales at which animals perceive their world. The hierarchical nature of habitat causes movement path structure to vary with spatial scale, and the patchy nature of habitat causes movement path structure to vary throughout space. These responses can be measured by a combination of path tortuousity (measured with fractal dimension) vs spatial scale, the variation in tortuousity of small path segments along the movement path, and the correlation between tortuousities of adjacent path segments. These statistics were tested using simulated animal movements. When movement paths contained no spatial heterogeneity, then fractal D and variance continuously increased with scale, and correlation was zero at all scales. When movement paths contained spatial heterogeneity then fractal D sometimes showed a discontinuity at transitions between domains of scale, variation showed peaks at transitions, and correlations showed a statistically significant positive value at scales smaller than patch size, decreasing to below zero at scales greater than patch size. I illustrated these techniques with movement paths from deer mice and red-backed voles. These new analyses should help understand how animals perceive and react to their landscape structure at various spatial scales, and to answer questions about how habitat structure affects animal movement patterns.
Nams, V.O. and M. C. Bourgeois (2004). Using fractal analysis to measure habitat use at different spatial scales: an example with marten. Can. J. Zool. 82:1738-1747.
Abstract:
Habitat selection is traditionally assessed by how much time the animal spends in each habitat type; however, one can obtain additional information by analysing the structure of the movement paths. We followed and mapped snow-tracks of American marten (Martes americana Turton, 1806). Using a new method to test the movement paths for deviations from a correlated random walk model, we show that these paths fail the test. This led to an analysis of fractal dimension vs spatial scale, which showed a natural break in fractal dimension at a scale of approximately 3.5 m, suggesting that marten displayed different responses to their micro-environment in two regions of spatial scale. Marten travel was more direct at scales below 3.5m than above 3.5m. Path tortuousity was affected by habitats at smaller scales but not at larger ones, indicating different responses by marten to their environment at these two ranges of scale. Multiple regression identified canopy closure and presence of conifer in the understory as variables affecting movement patterns at the 1-3.5 m scale. Fractal analysis of movement patterns provides a unique approach to examining habitat use as well as a means to identify the spatial scales at which an animal responds to its habitat.
Nams, V. O. and E. A. Gillis (2003). Changes in responses of small mammals to tracking tubes with time. J. Mammalogy 84:1374-1380
Abstract:
Refinements of a tracking tube technique for indices of small mammal populations are presented. Tracking tubes are 1˝" ABS plastic tubes with white paper inside, upon which has been attached a square of paper smeared with a carbon black:oil mixture. Tests showed that the best paper for the paper square is butcher paper, with the smooth side up, glued on with a glue stick. The best oil is heavy mineral oil, used in a 2.5:1 CB:oil ratio. The mixture tends to dry out after two weeks, so the papers should be replaced after about two weeks in the field. We also present a design for a holder to carry replacement papers, and a modified tube design which minimizes wetting by rain. The effects of time on the response of animals to the tracking tubes was measured. Over a period of 4 weeks, small mammals increased in their propensity to enter tubes, without any sign of leveling off. There were no differences among mice, voles and shrews. Thus when designing studies using tracking tubes one cannot simply adjust for differences in times by calculating a tracks/tube-night measure. Suggestions are given for how to handle this situation. Tests also showed that mammals more likely enter tracking tubes when they are placed near some microhabitat structure such as logs or stumps.
Nams, V. O, G. Mowat, and M. A. Panian (submitted to J. Applied Ecology) Scale dependent habitat selection by grizzly bears.
Abstract:
1. Grizzly bear abundances were sampled by identifying hairs at bait stations during the spring and summer, in British Columbia, Canada. Habitat variables (elevation, slope, aspect, water, roads, human development, logged land, treed land, and avalanche chutes) were measured using remote sensing imagery. Bear abundance and habitat data were partitioned into effects at various spatial scales, in the range from 0.5 km to 40 km.
2. Grizzly bears were patchy in abundance at all spatial scales, with especially strong patches of size 0.5-2km. This patchiness was not the result of groupings of individual bears. Habitats were also patchy at all spatial scales, with especially strong patterns at small (1-2km) and intermediate-large spatial scales (10-40+km).
3. Bears selected for habitats at spatial scales of 40+km and 4-8km. At scales of 40+km, bears selected for (i) higher slopes and lower aspect, or (ii) higher slopes, more avalanche chutes, fewer roads and trees, higher elevations, less logged land and lower aspect. Within 15km areas, bears selected for 6km areas which are either at higher elevations, or at higher elevations and had fewer trees. We did not detect selection for habitats at small scales.
4. These results show three distinct domains of scale: at 0.5-2 km, bears and habitats are patchy, at 5-10km, bears select for habitats, and at 40+ km habitats are patchy and bears select for habitats.
5. This study is the first to test the suitability of spatial scale in wildlife management guidelines. The scales that bears select for habitats roughly correspond to the scales used in present grizzly bear management plans in British Columbia.
Gillis, E.A., and V.O. Nams. (1998) How red-backed voles (Clethrionomys gapperi pallescens) find habitats. Canadian J. Zoology 76:791-794.
Abstract:
The purpose was to discover how red-backed voles (Clethrionomys gapperi
pallescens) found preferred habitat patches. Two hypotheses tested were
that voles discover habitat patches by chance, or that they perceive them from
a distance and travel toward them.
The distance at which voles detected a wooded habitat was evaluated by
measuring the accuracy of orientation at different distances. Animals were
released in an unfamiliar grassland at one of five distances (0 - 20m) from the
boundary of an adjacent unfamiliar woodland and tracked using the spool and
line technique. At all distances, the voles oriented towards the woods.
However, their reaction was much weaker at farther distances. Thus, reaction to
the woods was not an "all or nothing response" - the closer the voles
came to the woods, the straighter their paths were and the more directly they
oriented towards the woods. This adds to our understanding of how habitat
fragmentation affects voles. A between-patch distance of 20 m does not
completely isolate red-backed voles, but the distance of a home range diameter
(60-70m) likely would.
Nams, V.O. J.A. Antos and G.A. Allen. (1998) Seedling Establishment in a Patchy Environment. Ecoscience 5(1):86-94
Abstract:
Models of gene flow in plants have often assumed a homogeneous landscape in which seed survivorship is independent of dispersal distance. However, most landscapes are patchy, which may have important implications for gene flow. We consider the situation where plants have already dispersed into an area, and consider the effects of the (1) proportion of uninhabitable patches; (2) proportion of habitable patches that are empty; (3) survivorship of plants; and (4) proportion of seed dispersed out of the patch of origin. We looked at the effects of these on the ratio of mean seedling establishment distance to mean seed dispersal distance. For most combinations of these parameters, mean seed dispersal distance is an underestimate of gene flow. This effect can be large when most seeds remain in the parent patch, a situation common in nature. The model predicts that dispersal increases as the number of local patches becoming temporarily extinct increases, while dispersal increases, as the number of permanently empty patches increases.
Nams, V.O. (1997) Density-dependent predation by skunks using olfactory search images. Oecologia 110:440-448.
Abstract:
The formation of search images can create density-dependent predation.
Predators have been shown to form search images when searching for many small
prey items in one feeding session. This paper reports experiments that test
whether striped skunks can form olfactory search images in other situations:
when prey are found over several days, when prey are large, and when prey are
found in certain habitats.
Striped skunks were raised in captivity, and their reaction distance to food
was measured outside in a natural grassy area. In experiment #1 skunks were
offered many small food items for several days in a row. From one day to the
next, skunks initially detected food from further away, they increased
detection distance faster and their maximum detection distance increased --
i.e. they formed olfactory search images faster and stronger from one day to
the next. In experiment #2 skunks formed search images over several days when
finding only one large food item per day. In experiment #3 skunks lost
olfactory search images when they entered habitats in which they had previously
searched for another type of food. These long term search images magnify the
effects of short-term search images, extend the effects of short term search
image to longer time spans, and affect
Nams, V.O. (1996) The VFractal: a new
estimator for fractal dimension of animal movement paths. Landscape Ecology
11:289-297.
Abstract:
Fractal measurements of animal movement paths have been used to analyze how
animals view habitats at different spatial scales. One problem has been the
absence of error estimates for fractal d estimators. To address this weakness,
I present and test 4 new estimators for measuring fractal dimension at
different spatial scales, along with estimates of their variation. The
estimators are based on dividing the movement path into pairs of steps, forming
V s, and then estimating various statistics from each V. I measured the
performance of these estimators by comparing them to the traditional divider d
method, using data generated by two different animal movement models. The
estimator based on the net distance between the two steps and the cos turning
angle was most accurate, giving estimates similar to those of the
traditionally-used divider d method. Precision increased with longer and
straighter paths. Strengths of this new estimator are that it can estimate
fractal d at different spatial scales, give an estimate of variation, and
combine data from many separate path segments which have been gathered at
various spatial scales.
Nams, V.O., N.F.G. Folkard and J.N.M. Smith
(1996). Nitrogen fertilization stimulates herbivory by snowshoe hares in the
boreal forest. Can. J. Zool.
Abstract:
We fertilized small plots in the boreal forest of the southwestern Yukon, Canada,
to see how herbivory was affected. We assessed snowshoe hare activity by
counting pellets, and estimated grazing on grass as the proportion of blades
eaten. After two years of fertilization, snowshoe hares spent more time on and
near the test plots with more fertilizer. More grass was grazed on those plots,
but not near them. Thus, herbivores were attracted to the general area of the
fertilized plots, but only grazed directly on the plots.
Boutin,S., C.K. Krebs, R. Boonstra, M.R.T.
Dale, S.J. Hannon, K. Martin, A.R.E. Sinclair, J.N.M. Smith, R. Turkington, M.
Blower, A. Byrom, F.I. Doyle, C. Doyle, D. Hik, L. Hofer, A. Hubbs, T. Karels,
D.L. Murray, V.O. Nams, M. O Donaghue, C. Rohner, S. Schweiger. (1995). Population
changes of the vertebrate community during a snowshoe hare cycle in Canada
s boreal forest. Oikos 74:69-80.
Abstract:
We measured the density changes of 22 species of vertebrates during a
snowshoe cycle in northern Canada. Hares were the dominant herbivore in the
system and changes in their numbers were correlated with changes in numbers of
arctic ground squirrel, spruce grouse, ptarmigan, lynx, coyote, great horned
owl, goshawk, raven and hawk owl. Hare numbers were not correlated with numbers
of red-backed vole which showed peaks during the low, increase, and early
decline phases of the hare cycle. Hawk owls were the only predator whose
numbers correlated with changes in red-backed voles while boreal owls and weasels
were correlated with densities of Microtus. Red squirrel, American kestrel,
red-tailed hawk, northern harrier, wolverine, magpie, and gray jay showed no
correlation with hare or vole numbers. We conclude that species in the boreal
forests of Canada do not exhibit the strong synchrony found between voles and
other members of the vertebrate community in northern Fennoscandia. We discuss
some of the possible reasons for these differences.
Murray, D.L., S. Boutin, M. O'Donnoghue, V.O.
Nams(1995) Hunting behaviour of sympatric felids and canids in relation to
vegetative cover. Animal Behaviour 50:1203-1210.
Abstract:
Carnivore foraging behaviour is suited for hunting in specific vegetative cover
types and therefore is largely stereotypical within taxonomic families. Felids
typically employ dense cover to stalk or ambush prey, whereas canids do not
make use of vegetation when hunting. Sympatric lynx, Lynx canadensis, and
coyotes, Canis latrans, were tracked in snow for three winters and hunting
behaviour in relation to vegetative cover was examined. The major prey of both
species was snowshoe hare, Lepus americanus. Lynx chased hares more frequently
in sparse spruce, Picea glauca, canopy than coyotes, whereas coyotes chased
hares more often in dense spruce than lynx. Lynx initiated chases by stalking
in sparse spruce and by ambushing from beds in dense spruce. Vegetative cover
did not affect lynx hunting success, but lynx did have higher success when
ambushing versus stalking hares. Coyotes chased hares from closer proximity
than lynx and employed a pouncing hunting behaviour. Coyote chases were shorter
and more successful in dense versus sparse forest. It is concluded that lynx
hunting behaviour is variable according to cover, whereas that of coyotes is
fixed. However, coyotes appeared to use vegetation as concealment when
approaching hares: the possible influence of snow on hunting tactics of each
predator species is discussed. (C) 1995 The Association for the Study of Animal
Behaviour
Nams, V.O. (1994). Increasing sampling
efficiency of lowbush blueberries. Can. J. Plant Science. 74:573-576
Abstract:
Yield estimates of lowbush blueberries (Vaccinium angustifolium) are
highly variable. Two techniques for estimating cover and five quadrat sizes for
estimating stem density were tested in an attempt to minimize this variability.
The most efficient technique for estimating cover is pacing for 100 footsteps
and counting the number of footsteps falling within blueberry patches. The most
efficient quadrat size for estimating stem density within blueberry patches is
0.025m2. Variability due to observers accounted for 23% of the variance in stem
density estimates, but decreased to 4% with a short training session at the
start of each field and sampling day.
Nams, V.O., N.F.G. Folkard and J.N.M. Smith
(1993). Effects of nitrogen fertilization on several woody and non-woody
boreal forest species. Can. J. Bot. 71:93-97
Abstract:
The effects of three levels of fertilizer were tested on the growth of several
woody and non-woody plants from a boreal forest community in the south west Yukon.
The effects of fertilization were assessed by clipping ground layer vegetation
and measuring twig growth at the end of the second summer. Over the two years
of fertilization there were significant increases in growth over control levels
for perennial grasses (Festuca altaica and Calamagrostis lapponica),
two herbs (Epilobium angustifolium and Achillea millefolium), and
two deciduous shrubs (Salix glauca and Betula glandulosa).
However, the growth of white spruce trees (Picea glauca) increased only
slightly in response to increasing nitrogen levels, and the evergreen dwarf
shrub Arctostaphylos uva-ursi showed no response.
Nams, V.O. 1991. Olfactory
search images in striped skunks. Behaviour 119:267-284.
Abstract:
Striped skunks (Mephitis mephitis) which had been raised in
captivity can increase their reaction distance to the smell of a given food.
This reaction distance decreases after they find other types of foods, using
either sound or smell. This decrease could be a result of skunks increasing
preference for specific food, or shifting attention onto the smell of specific
food. However, other experiments showed that skunks do not change prey
preference. Therefore the decrease in reaction distance is likely due to skunks
shifting attention to the smell of specific food. I suggest that this is the
olfactory analogue to visual search images-i.e. olfactory search images.
Nams, V.O. 1989. Effects of radiotelemetry
error on sample size and bias when testing for habitat selection. Can. J.
Zoology 67: 1631-1636.
Abstract:
Radiolocations of animals by triangulation have certain errors. I show how the
ratio of telemetry error to habitat size affects efficiency of testing for
habitat selection and how to estimate sample size when telemetry error is
large. When telemetry error is more than 1.5 times average habitat size, the
required sample size increases immensely. When telemetry error is large,
measurements of habitat selection are biased. I present a technique to remove
the bias and estimate the habitat selection one would observe if telemetry
error were zero.
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