No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A conceptual model for migratory tundra caribou to explain and predict why shifts in spatial fidelity of breeding cows to their calving grounds are infrequent.
Abstract
ABSTRACT: Calving grounds of migratory tundra caribou (Rangifer tarandus) have two prominent characteristics. Firstly, the cows are gregarious, and secondly, the annual calving grounds spatially overlap in consecutive years (spatial fidelity). The location of consecutive annual calving grounds can gradually shift (either rotationally or un-directional) or more rarely, abruptly (non-overlapping). We propose a mechanism to interpret and predict changes in spatial fidelity. We propose that fidelity is linked to gregariousness with its advantages for individual fitness (positive density-dependence). Our argument is based on a curvilinear relationship between the density of cows on the calving ground (which we use to index gregari-ousness) and spatial fidelity. Extremely high or low densities are two different mechanisms which can lead to reduced spatial fidelity to annual calving grounds and reflect the caribou's adaptive use of its calving ranges.
... This herd moves annually between their more southern winter grounds and their calving and summer ranges further north. Caribou do not always display high inter-annual fidelity to their wintering grounds [35] but, in part due to the gathering of large herds which facilitates social learning, the herd has displayed high fidelity to their calving grounds for at least 40 years [39]. Pregnant females that arrive on the calving grounds give birth to their calves shortly after, and dramatically reduce their movement for up to two weeks [17,64]. ...
Background
Animals of many different species, trophic levels, and life history strategies migrate, and the improvement of animal tracking technology allows ecologists to collect increasing amounts of detailed data on these movements. Understanding when animals migrate is important for managing their populations, but is still difficult despite modelling advancements.
Methods
We designed a model that parametrically estimates the timing of migration from animal tracking data. Our model identifies the beginning and end of migratory movements as signaled by change-points in step length and turning angle distributions. To this end, we can also use the model to estimate how an animal’s movement changes when it begins migrating. In addition to a thorough simulation analysis, we tested our model on three datasets: migratory ferruginous hawks (Buteo regalis) in the Great Plains, barren-ground caribou (Rangifer tarandus groenlandicus) in northern Canada, and non-migratory brown bears (Ursus arctos) from the Canadian Arctic.
Results
Our simulation analysis suggests that our model is most useful for datasets where an increase in movement speed or directional autocorrelation is clearly detectable. We estimated the beginning and end of migration in caribou and hawks to the nearest day, while confirming a lack of migratory behaviour in the brown bears. In addition to estimating when caribou and ferruginous hawks migrated, our model also identified differences in how they migrated; ferruginous hawks achieved efficient migrations by drastically increasing their movement rates while caribou migration was achieved through significant increases in directional persistence.
Conclusions
Our approach is applicable to many animal movement studies and includes parameters that can facilitate comparison between different species or datasets. We hope that rigorous assessment of migration metrics will aid understanding of both how and why animals move.
... Second, the effects of caribou on ecosystem processes and nutrient cycling via their role as grazers has been studied in depth (Stark and Grellmann 2002, Lindwall et al. 2013 and their creation of local nutrient hotspots from feces (van der Wal et al. 2004, Barthelemy et al. 2015, urine (Barthelemy et al. 2018) and carcasses (Swanson 1979) has begun to be studied, but the implication of these cumulative effects on landscape patterning has not. Caribou herds also have discrete population events in which they aggregate, such as calving events (Gunn et al. 2012, Campeau et al. 2019. Finally, many populations of caribou are in rapid decline globally (Vors and Boyce 2009); hence, it is important to understand the potential role they play in sustaining tundra and boreal ecosystems via spatial nutrient redistribution. ...
Animals can be important vectors of nutrient transfer within and across landscapes, with important implications for ecosystem productivity and composition. While it is presumed large ungulates are agents of nutrient dispersal via movement and activity, research analyzing their net effects on landscapes remains scarce. We present an individual‐based model that investigates how caribou affect the distribution of nutrients on a landscape through consumption only, as well through the cumulative effects of consumption and nutrient deposition (i.e. fecal waste and carcass deposition). We explored these dynamics in simulations that altered the context of environments, either initially containing heterogeneous or homogeneous nutrient distributions, animal densities and sociality of caribou behavior. In the consumption‐only simulations, caribou density and sociality created different patterns of heterogeneity at both the landscape and local scale depending on the initial landscape conditions. In these simulations, caribou populations crashed at high densities because the lack of animal deposition resulted in low resources across the landscape. This was not the case when considering the cumulative effects of consumption and deposition, indicating the return of nutrients from animals may be important for population stability. Additionally, in simulations considering the cumulative effects of caribou, increasing caribou density increased landscape heterogeneity irrespective of the initial condition (i.e. heterogeneous and homogeneous landscapes), and maintained or increased local heterogeneity in heterogeneous and homogenous landscape, respectively. Importantly, in all simulations the net impact of caribou at the individual patch level was extremely variable, suggesting that animal inputs are highly varied throughout the landscape. Our results indicate the movement of large ungulates such as caribou can increase the heterogeneity of available nutrients within a landscape and provide an important feedback for population stability. Thus, the loss of large ungulates from natural ecosystems via anthropogenic activity is likely to result in less heterogeneous natural landscapes.
... We defined fidelity as the tendency of an animal to return to its previously used location in consecutive years [59][60][61]. To analyze the annual fidelity of individual caribou to wintering areas, we calculated transition probabilities using the R package TraMineR [62]. ...
Many animals migrate to take advantage of temporal and spatial variability in resources. These benefits are offset with costs like increased energetic expenditure and travel through unfamiliar areas. Differences in the cost-benefit ratio for individuals may lead to partial migration with one portion of a population migrating while another does not. We investigated migration dynamics and winter site fidelity for a long-distance partial migrant, barren ground caribou (Rangifer tarandus granti) of the Teshekpuk Caribou Herd in northern Alaska. We used GPS telemetry for 76 female caribou over 164 annual movement trajectories to identify timing and location of migration and winter use, proportion of migrants, and fidelity to different herd wintering areas. We found within-individual variation in movement behavior and wintering area use by the Teshekpuk Caribou Herd, adding caribou to the growing list of ungulates that can exhibit migratory plasticity. Using a first passage time–net squared displacement approach, we classified 78.7% of annual movement paths as migration, 11.6% as residency, and 9.8% as another strategy. Timing and distance of migration varied by season and wintering area. Duration of migration was longer for fall migration than for spring, which may relate to the latter featuring more directed movement. Caribou utilized four wintering areas, with multiple areas used each year. This variation occurred not just among different individuals, but state sequence analyses indicated low fidelity of individuals to wintering areas among years. Variability in movement behavior can have fitness consequences. As caribou face the pressures of a rapidly warming Arctic and ongoing human development and activities, further research is needed to investigate what factors influence this diversity of behaviors in Alaska and across the circumpolar Arctic.
... Chapter 3 TERRESTRIAL AND FRESHWATER SYSTEMS frequently, but changes are also becoming evident in what were considered to be very constant calving grounds. During 42 years of monitoring the Bathurst herd, the average annual overlap in calving grounds was 43%, forming two geograph- ically consistent clusters (1966-1984 and 1996-2011), broken by a brief period at peak caribou densities when the calving ground shifted ( Gunn et al. 2012). In early springs plants tend to grow and flower earlier, and calving grounds tend to have high concentrations of plants that provide a burst of nutrient-rich early growth that is crucial to caribou milk production ( Griffith et al. 2002). ...
... Based on Bergerud's (1996Bergerud's ( , 1988 observations and definitions of ecotypes, migratory caribou move north of treeline at calving to areas of lower wolf density. In Ontario, however, the migratory southern Hudson Bay caribou population, constrained by the Hudson Bay coastline, has only 5% of its annual range north of treeline (Gunn et al., 2012;Newton et al., 2015). The Hudson Bay Lowland, in contrast to the boreal forest to the south, has lower wolf densities (Berglund et al., 2014;Patterson, 2009;Poley et al., 2014). ...
... The herd was estimated at 32,000 animals (±5300 SE) in 2009 representing a 70 % decline over 3 years (Adamczewski et al. 2009). The distribution of barren-ground caribou is density dependent such that range expansion and contraction are a function of the size of the herd (Simmons et al. 1979;Bergerud et al. 1984;Heard and Calef 1986;Messier et al. 1988;Couturier et al. 1990;Gunn et al. 2012). Gunn et al. (2013) reported that the winter range of the Bathurst herd has contracted since 2002, corresponding to the decline in the herd. ...
Wolves (Canis lupus) that den on the tundra of the central Arctic prey primarily on migratory barren-ground caribou (Rangifer tarandus groenlandicus). Prey densities in the vicinity of den sites are low, however, for a period each summer when caribou migrate to their calving and post-calving ranges. Eskers provide substrate where wolves can excavate den sites, but these landforms make up only a small proportion of the tundra landscape. We investigated the factors that influenced den site selection for wolves on the summer range of the Bathurst caribou herd, Northwest Territories, Canada. We used a long-term data set (1996–2012) of wolf den locations to develop a series of resource selection function (RSF) models representative of broad land-cover types, esker density, and annual variation in seasonal prey availability. We compared a temporal sequence of RSF models to investigate whether wolves altered selection patterns in response to a 90 % decline in caribou abundance (1996–2012). Eskers were selected denning habitat; the distribution of eskers may be limiting when wolf density is high. Covariates representing the seasonal distribution of caribou from early (5–18 July) and late (19 July–22 August) summer were the best predictors of den occurrence; these areas represented reliable availability of caribou over the greatest portion of the denning period. As the caribou herd declined, the seasonal summer ranges contracted northward towards the calving ground. Wolves did not exhibit a similar response. As such, the period of spatial separation between breeding wolves at den sites and the main distribution of caribou increased when herd abundance was low. The lack of a behavioural response is consistent with wolf–prey dynamics observed in other studies that suggest wolves strive to maintain consistent territories even following large decreases in resource availability. Such behaviours reduce fitness and have implications for pup survival and population growth.
... The Buchans herd appeared to be the most effective at avoiding predation, which is interesting given that it is the herd that undergoes the longest annual migration to calving grounds (Mahoney and Schaefer 2002a). This suggests that migratory caribou may face a trade-off between migration distance and its expected benefit in terms of reduced predation risk and increased foraging opportunities (Gunn et al. 2012); such a trade-off is likely to exist in terrestrial species given the high costs associated with migratory behaviour (Alerstam et al. 2003). Considering the observed variability in Newfoundland caribou migratory movements (Rayl et al. 2014), it appears that this trade-off may lead to variable migratory behaviour across herds. ...
Habitat selection is a multi-level, hierarchical process that should be a key component in the balance between food acquisition and predation risk avoidance (food – predation trade-off ). However, to date, studies have not fully elucidated how fine- and broad-scale habitat decisions by individual prey can help balance food versus risk. We studied broad-scale habitat selection by Newfoundland caribou Rangifer tarandus , focusing on trade-off s between predation risk versus access to forage during the calving and post-calving period. We improved traditional measures of habitat availability by incorporating fine-scale movement patterns of caribou into the availability kernel, thus enabling separation of broad and fine scales of selection. Remote sensing and fi eld surveys served to create a spatio-temporal model of forage availability, whereas GPS telemetry locations from 66 black bears Ursus americanus and 59 coyotes Canis latrans provided models of predation risk. We then used GPS telemetry locations from 114 female caribou to assess food – predation trade-offs through the prism of our refi ned model of caribou habitat availability. We noted that migratory movements of caribou were oriented mainly towards habitats with abundant forage and lower risk of bear and (to a lesser extent) coyote encounter. These findings were generally consistent across caribou herds and would not have been evident had we used traditional methods instead of our refined model when estimating habitat availability. We interpret these fi ndings in the context of stereotypical migratory behaviour observed in Newfoundland caribou, which occurs despite the extirpation of wolves Canis lupus nearly a century ago. We submit that caribou are able to balance food acquisition against predation risk using a complex set of factors involving both finer and broader scale selection. Accordingly, our study provides a strong argument for using refined habitat availability estimates when assessing food – predation trade-offs.
... Notwithstanding this, we contend that our approach offers transparent and conservative results regarding selection because the analyses summarized individual selection and then pooled the individual responses into herds rather than a more uniform (and less appropriate) multiherd pooling.The Buchans herd appeared to be the most effective at avoiding predation, which is interesting given that it is the herd that undergoes the longest annual migration to calving grounds(Mahoney & Schaefer 2002b). This suggests that migratory caribou may face a trade-off between migration distance and its expected benefit in terms of reduced predation risk and increased foraging opportunities(Gunn, Poole & Nishi 2012); such a trade-off is likely to exist in terrestrial species given the high costs ...
The objective of this thesis is to better understand the demography and habitat
selection of Newfoundland caribou. Chapter 1 provides a general introduction of
elements of population ecology and behavioural ecology discussed in the thesis. In
Chapter 2, I examine the causes of long-term fluctuations among caribou herds. My
findings indicate that winter severity and density-dependent degradation of summer
range quality offer partial explanations for the observed patterns of population change.
In Chapter 3, I investigate the influence of climate, predation and density-dependence
on cause-specific neonate survival. I found that when caribou populations are in a
period of increase, predation from coyotes and bears is most strongly influenced by the
abiotic conditions that precede calving. However, when populations begin to decline,
weather conditions during calving also influenced survival. I build on this analysis in
Chapter 4 by determining the influence of climate change on the interplay between
predation risk and neonate survival. I found that the relative equilibrium between bears
and coyotes may not persist in the future as risk from coyotes could increase due to
climate change. In Chapter 5, I investigate the relationships in niche overlap between
caribou and their predators and how this may influence differential predation risk by
affecting encounter rates. For coyotes, seasonal changes in niche overlap mirrored iii
variation in caribou calf risk, but had less association with the rate of encounter with
calves. In contrast, changes in niche overlap during the calving season for black bears
had little association with these parameters. In Chapter 6, I examine broad-level habitat
selection of caribou to study trade-offs between predator avoidance and foraging
during the calving season. The results suggest that caribou movements are oriented
towards increased access to foraging and the reduction of encounter risk with bears,
and to a lesser extent, coyotes. Finally, I synthesize the major findings from this thesis
and their relevance to caribou conservation in Chapter 7, to infer that Newfoundland
caribou decline is ultimately driven by extrinsic and intrinsic elements related to
density-dependence. Reduction in neonate survival emerged from nutritionally-stressed
caribou females producing calves with lower survival.
... This fundamental relationship is exemplified by species like caribou (Rangifer tarandus (L., 1758)) where changes in population size and space use often vary in concert. Numbers of migratory caribou may rise or fall by 100-fold in a few decades (Bergerud 1996; Vors and Boyce 2009; Couturier et al. 2010; Mahoney et al. 2011), swings in demography that may move in tandem with size of the home range (Schaefer and Wilson 2002; Couturier et al. 2010), fidelity to calving grounds (Gunn et al. 2012), and timing of migration (Mahoney and Schaefer 2002). Population structure, too, may be altered (Hinkes et al. 2005). ...
Understanding the relationship between abundance and distribution is central to ecology but may require broad-scale observations, especially for long-lived, mobile animals like caribou (Rangifer tarandus (L., 1758)). We tested the link between demography and spatial ecology of Newfoundland caribou, coincident with their numerical growth (1980s, 1990s) and decline (2000s). We analysed site fidelity, rate of movements, timing of migration, and population organization from telemetry observations of more than 600 adult females. Site fidelity was consistent across herds, intensifying near the onset of calving and peaking in late summer, a cycle that may reflect selection for postpartum security. Late-summer fidelity was stronger in the 1980s than 1990s, a trend that reversed itself during the 2000s. Weekly movements were lower in the 2000s, but with no clear differences between the 1980s and 1990s. Timing of migration changed: in the 2000s, spring migration of the Buchans herd occurred 3 weeks earlier and autumn migration 3 weeks later compared with the previous decade, the reversal of a 40-year trend. Herd affinities, revealed by fuzzy membership coefficients, diminished by the 2000s. These changes are consistent with the hypothesis of limitation by summer forage competition. Space use represents a useful gauge of numerical changes in caribou.
How animals use their range can have physiological, ecological, and demographic repercussions, as well as impact management decisions, species conservation, and human society. Fidelity, the predictable return to certain places, can improve fitness if it is associated with high-quality habitat or helps enable individuals to locate heterogenous patches of higher-quality habitat within a lower-quality habitat matrix. Our goal was to quantify patterns of fidelity at different spatial scales to better understand the relative plasticity of habitat use of a vital subsistence species that undergoes long-distance migrations. We analyzed a decade (2010-2019) of GPS data from 240 adult, female Western Arctic Herd (WAH) caribou (Rangifer tarandus) from northwest Alaska, U.S.A. We assessed fidelity at 2 spatial scales: to site-specific locations within seasonal ranges and to regions within the herd's entire range by using 2 different null datasets. We assessed both area and consistency of use during 6 different seasons of the year. We also assessed the temporal consistency of migration and calving events. At the scale of the overall range, we found that caribou fidelity was greatest during the calving and insect relief (early summer) seasons, where the herd tended to maximally aggregate in the smallest area, and lowest in winter when the seasonal range is largest. However, even in seasons with lower fidelity, we found that caribou still showed fidelity to certain regions within the herd's range. Within those seasonal ranges, however, there was little individual site-specific fidelity from year to year, with the exception of summer periods. Temporally, we found that over 90% of caribou gave birth within 7 days of the day they gave birth the previous year. This revealed fairly high temporal consistency, especially given the spatial and temporal variability of spring migration. Fall migration exhibited greater temporal variability than spring migration. Our results support the hypothesis that higher fidelity to seasonal ranges is related to greater environmental and resource predictability. Interestingly, this fidelity was stronger at larger scales and at the population level. Almost the entire herd would seek out these areas with predictable resources, and then, individuals would vary their use, likely in response to annually varying conditions. During seasons with lower presumed spatial and/or temporal predictability of resources, population-level fidelity was lower but individual fidelity was higher. The
Barren ground caribou (Rangifer tarandus granti) are distributed in herds that seasonally use specific geographic regions within an annual range, with varying levels of fidelity during different periods (e.g., calving, insect relief, wintering). As a result, caribou management is generally tailored to individual herds that often range across administrative boundaries. Herd ranges can shift over time, seasonal ranges of adjacent herds often overlap, herds merge, and there is often little genetic differentiation among adjacent herds. If substantial herd interchange occurs, it would have important management implications by influencing estimates of herd size, herd composition, and harvest rates. We compiled satellite telemetry data from 2003–2015 for 4 large arctic caribou herds to quantify herd interchange rates. We calculated a metric of herd interchange based on the relationship of caribou locations to typical weekly herd ranges (all yrs combined) and the distance to other radio‐collared caribou from each of the 4 herds (yr specific). Although herd membership cannot always be clearly defined based on location, this metric provides an objective measure of the strength of evidence of herd membership that can be used to make comparisons among herds and time periods. We also calculated herd overlap and quantified how it varied throughout the year. Herd interchange was rare in the 2 larger herds, generally occurring when caribou overwintered with an adjacent herd, whereas herd interchange from the 2 smaller herds was more frequent and could last longer than a year. Although sample sizes were limited, there were no clear patterns in herd interchange with year or annual herd size. The 2 smaller herds had large seasonal overlap with adjacent herds, suggesting that herd interchange may be related to spatiotemporal herd overlap and relative herd size. Our results can help managers understand herd interchange and overlap to make management decisions, interpret research results, and develop more accurate population models. © 2020 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society. The amount of herd overlap and interchange varied among 4 arctic caribou herds in northern Alaska, USA, and Yukon Territories, Canada. Caribou from the 2 larger herds rarely switched herds and herd interchange occurred more frequently for caribou of the 2 smaller herds.
The severity of recent declines of barren-ground caribou (Rangifer tarandus groenlandicus) across the central Canadian Arctic has led to harvest restrictions and concerns about population recovery. Wolves (Canis lupus) are the main predator of barren-ground caribou; however, the extent that wolves influence the decline and recovery of caribou herds is unknown. Such uncertainty confounds management responses (e.g., reducing harvest, predator control). We investigated wolf–caribou dynamics on the summer range of barren-ground caribou in the Northwest Territories and Nunavut, Canada (i.e., Bathurst caribou herd). Our primary objective was to test for a numerical response of wolves to changes in the abundance and spatial distribution of caribou. Caribou experienced a >90% decline in abundance over the study period (1996–2014). Using long-term data sets (1996–2012), we developed regression models to investigate relationships between abundance indices of wolves and range-use patterns of caribou. We monitored the movements of adult female wolves fitted with global positioning system (GPS) collars representing individual packs throughout the 2013 and 2014 denning periods. We also investigated pup recruitment, an index of population decline, at a time of low caribou abundance. Finally, we developed a series of stochastic population models to understand how pup recruitment influenced wolf densities on the Bathurst range over the period of caribou decline. As caribou abundance decreased, the late-summer distribution of the Bathurst herd contracted toward the calving ground. These movements correlated with low rates of wolf pup recruitment and high den abandonment, suggesting a regulatory mechanism whereby wolf reproductive success was limited by the low availability of caribou within the denning areas. Furthermore, these data suggested a numerical response, where wolf densities decreased as caribou numbers declined. In 2014, wolf density was estimated at <4 wolves/1,000 km2. Our results suggest that these wolves exhibited a relatively strong numerical response to a single, declining prey base. Given the continued decline in the Bathurst caribou herd, the tundra wolf population on the Bathurst range has likely declined below our 2014 estimate.
Aim
Drivers of biodiversity loss are increasingly broad in scale, requiring conservation planning to move towards range‐wide assessments. This is especially challenging for migratory species, such as reindeer or caribou ( Rangifer tarandus ), which use only a small portion of their range at a given point in time, and for which some parts of their range, such as calving grounds, may be much more important than others. Our aim was to identify potential calving ground habitat of wild tundra reindeer populations throughout Russia, where scarce knowledge about seasonal reindeer habitat is an obstacle for conservation planning, and to assess possible impacts from oil and gas development and climate change.
Location
Northern Eurasia.
Method
We used occurrence data from known reindeer calving grounds using species distribution models to first assess calving grounds characteristics and second predict their distribution across the Russian Arctic. We then compared our calving ground map with maps of oil and gas development, and a range of climate change indicators.
Results
We found areas throughout the Russian Arctic that are suitable for calving, including for some wild reindeer populations where calving ground locations are unknown. Variables relating to resource availability in spring and predator avoidance were the strongest predictors in our model. Oil and gas development affects calving grounds especially in the Barents Sea region and in south‐western Siberia, whereas climate change affects calving grounds on Taymyr, Chukotka, and Kamchatka.
Main conclusions
We conducted the first assessment of calving grounds of Russia's wild reindeer populations, highlighting the spatial heterogeneity of the threats that they may face. Given the potentially strong impact of oil and gas development and climate change, conservation planning should aim for designing resilient conservation networks that would allow Arctic biodiversity to freely move in time and space and thus to adapt to changing environments.
Intensities of warble fly larvae, Hypoderma tarandi (L.), were examined in slaughtered reindeer (Rangifer tarandus tarandus L.) from different summer grazing areas of Finnmark County, northern Norway. To test the hypothesis-that larval abundance decreases with increase in post-calving migration distance (i.e., distance from calving grounds), herds with differing migration distances were sampled. The prevalence of infection in the total sample of 1168 animals was 99.9%. The study revealed significant differences in larval abundance among herds from different summer grazing areas. Herds with post-calving migrations have significantly lower larval abundances than herds remaining on or near the calving grounds for the whole summer. Between-herds variation in abundance of H. tarandi larvae is assumed to reflect differing densities of the infective stage (adult flies) on the herds' summer ranges. Larval abundance in a herd is in turn negatively correlated with the distance between the main larval shedding areas (i.e., calving grounds) and the areas of greatest transmission (i.e., summer pastures). These results are discussed in relation to transmission of other parasites common to Rangifer and suggest that this host's post-calving migration may be a behavioural adaptation that reduces levels of parasitic infections.
The five naturally occurring and one transplanted caribou (Rangifer tarandus granti) herd in southwestern Alaska composed about 20% of Alaska's caribou population in 2001. All five of the naturally occurring herds fluctuated considerably in size between the late 1800s and 2001 and for some herds the data provide an indication of long-term periodic (40-50 year) fluctuations. At the present time, the Unimak (UCH) and Southern Alaska Peninsula (SAP) are recovering from population declines, the Northern Alaska Peninsula Herd (NAP) appears to be nearing the end of a protracted decline, and the Mulchatna Herd (MCH) appears to now be declining after 20 years of rapid growth. The remaining naturally occurring herd (Kilbuck) has virtually disappeared. Nutrition had a significant effect on the size of 4-month-old and 10-month-old calves in the NAP and the Nushagak Peninsula Herd (NPCH) and probably also on population growth in at least 4 (SAP, NAP, NPCH, and MCH) of the six caribou herds in southwestern Alaska. Predation does not appear to be sufficient to keep caribou herds in southwestern Alaska from expanding, probably because rabies is endemic in red foxes (Vulpes vulpes) and is periodically transferred to wolves (Canis lupus) and other canids. However, we found evidence that pneumonia and hoof rot may result in significant mortality of caribou in southwestern Alaska, whereas there is no evidence that disease is important in the dynamics of Interior herds. Cooperative conservation programs, such as the Kilbuck Caribou Management Plan, can be successful in restraining traditional harvest and promoting growth in caribou herds. In southwestern Alaska we also found evidence that small caribou herds can be swamped and assimilated by large herds, and fidelity to traditional calving areas can be lost.
Parturient female caribou from the Teshekpuk caribou (Rangifer tarandus granti) herd (TCH) have been observed across the western North Slope, but most cows that were seen with calves during the calving period were in the area surrounding Teshekpuk Lake. During surveys conducted between 1994 and 2003, 155 (91%) of 171 collared cows seen with calves were within an area given protected status in the 1998 Bureau of Land Management Final Integrated Activity Plan/Environmental Impact Statement (IAP/EIS). The percentage of adult collared cows seen with a calf between 1994 and 2003 has ranged from 44% to 86%, with a mean of 66%. The years with the lowest percentage of collared cows seen with calves were 1997 (50%) and 2001 (44%). In 1997 most of the herd migrated much farther south than usual, and in 2001 unusually deep, persistent snow restricted spring migration, resulting in fewer cows returning to the traditional calving area during the calving period. When snowmelt dates were earlier, calving locations were farther north. Average standardized travel rates for parturient cows were significantly greater before they had calves (7.25 km/day) than after 3.89 (km/day). Geographically, protections granted by the 1998 BLM IAP/EIS appear to adequately cover the concentrated calving grounds, allowing for variance in the annual distribution of calving cows.
We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23 000 in 1992, declined to 18 000 by 1995, and again increased to 27 000 by 2000. Net calf production was consistent with changes in herd size. In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within 4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for eastern females (e.g., 1988 - 94: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd. Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable natural environment.
Predator swamping was an adequate explanation for the occurrence of within-season reproductive synchrony when the predator exhibits a Holling type-II functional response (specialist predator), but, in the case of a generalist predator switching from alternative prey (Holling type-III functional response), which is expected to be a common functional-response type when particular prey are unavailable at certain times of the year, highly asynchronous reproduction may be the best reproductive strategy. In particular, when prey switching occurs at high offspring densities and/or the satiation density of the predator is high relative to the total reproduction of the prey population, the peak predation rate is expected to occur when reproduction is completely synchronous. Spatially clumped prey populations are expected to experience a dramatically increased predation rate if reproduction is synchronized within clumps but not between them. Hence, it is predicted that mechanisms promoting within-group reproductive synchrony are even less likely to have evolved as a predator-swamping strategy in patchily distributed populations, in which reproduction cannot be synchronized between groups. -from Author
Habitat selection is a crucial process in the life cycle of animals because it can affect most components of fitness. It has been proposed that some animals cue on the reproductive success of conspecifics to select breeding habitats. We tested this hypothesis with demographic and behavioral data from a 17-yr study of the Black-legged Kittiwake (Rissa tridactyla), a cliff-nesting seabird. As the hypothesis assumes, the Black-legged Kittiwake nesting environment was patchy, and the relative quality of the different patches (i.e., breeding cliffs) varied in time. The average reproductive success of the breeders of a given cliff was predictable from one year to the next, but this predictability faded after several years. The dynamic nature of cliff quality in the long term is partly explained by the autocorrelation of the prevalence of an ectoparasite that influences reproductive success. As predicted by the performance-based conspecific attraction hypothesis, the reproductive success of current breeders on a given cliff was predictive of the reproductive success of new recruits on the cliff in the following year. Breeders tended to recruit to the previous year's most productive cliffs and to emigrate from the least productive ones. Consequently, the dynamics of breeder numbers on the cliffs were explained by local reproductive success on a year-to-year basis. Because, on average, young Black-legged Kittiwakes first breed when 4 yr old, such a relationship probably results from individual choices based on the assessment of previous-year local quality. When breeders changed breeding cliffs between years, they selected cliffs of per capita higher reproductive success. Furthermore, after accounting for the potential effects of age and sex as well as between-year variations, the effect of individual breeding performance on breeding dispersal was strongly influenced by the average reproductive success of other breeders on the same cliff. Individual breeding performance did not appear to influence the probability of dispersing for birds breeding on cliffs with high local reproductive success, whereas individual breeding performance did have a strong effect on dispersal for birds that bred on cliffs with lower local reproductive success. This suggests that the reproductive success of locally breeding conspecifics may be sufficient to override an individual's own breeding experience when deciding whether to emigrate. These results, which are supported by behavioral observations of the role of prospecting in recruitment, suggest that both first breeders and adults rely on the reproductive success of conspecifics as 'public information' to assess their own chances of breeding successfully in a given patch and to make settling decisions. A corollary prediction is that individuals should attempt to breed near successful conspecifics (a form of social attraction) in order to benefit from the same favorable local environmental conditions. Such a performance-based conspecific attraction mechanism can thus lead to an aggregative distribution of nests and may have played a role in the evolution of coloniality.
A reduction in individual vigilance with an increase in group size is one of the most frequently reported relationships in the study of animal behaviour. It has been argued that this phenomenon may not be a direct consequence of an increase in group size but may be due to other factors relating to increased group size, such as increased foraging competition. However, there is evidence for a direct relationship between group size and vigilance where other variables have been controlled. The aim of this review is to highlight the fact that the functional explanation of the group size effect remains unclear. Some authors have considered just one hypothesis, the group vigilance or ‘many eyes’ hypothesis. This states that, by taking advantage of the vigilance of other group members, individuals can reduce their own vigilance. However, there is an alternative, or additional, possibility that if individual vigilance declines with a reduction in individual predation risk, the group size effect could be accounted for by a reduction in individual risk at higher group sizes, as is widely thought to occur through encounter, dilution and confusion effects. In this review, it is shown that evidence previously interpreted in terms of one hypothesis may also be interpreted in terms of the other. Future research should be directed towards explicit consideration of the two effects and empirical tests to distinguish their relative importance. It is proposed that the individual risk hypothesis, with group vigilance as one element, provides a more general framework for understanding variation in vigilance behaviour with group size and with other factors.
The range used for calving and for the first month of lactation by the Riviere George Caribou Herd (RGH), which peaked at over 600 000 individuals in the mid-eighties, showed signs of overgrazing, in contrast to that used by the adjacent Riviere aux Feuilles Herd. Density of females in the tundra habitat below 600 m asl averaged 11.2 animals/km(2) on the overgrazed range in 1988, in comparison with approximate to 0.5/km(2) on the other range. Inadequate foraging conditions during the first month of lactation caused complete exhaustion of fat reserves in females on the poor range; milk production was seemingly insufficient, as calves were lighter and grew at a slower rate than calves born on the better summer range or born in captivity from dams fed ad libitum. Moreover, females on the poor range were shorter and lighter than their counterparts on the good range, illustrating that priority goes to reproduction rather than to growth under suboptimal foraging conditions. Accretion of body fat and protein in RGH females was rapid in autumn, but individuals with a calf at yield accumulated smaller fat reserves than nonreproductive adult females. Condition did not affect ovulation. However, interruption of gestation was suspected in females that were unable to accumulate enough body reserves in autumn or early winter, judging from the progressive decline in the pregnancy rate and in the autumn cow:calf ratio observed for the RGH since 1984, concomitant with the levelling off of the herd. Summer nutrition seemingly regulated the RGH through a combination of decreased fecundity and survival.
Individual differences in body mass exert a major influence on several life-history traits of mammals. We investigated the factors influencing variation in body mass of calves of migratory caribou (Rangifer tarandus) at birth (June, 19 years of data) and in autumn (October, 15 years of data) in the Rivière-aux-Feuilles (Feuilles, 1991–2003) herd and the Rivière-George (George, 1978–2003) herd in Québec and Labrador, Canada. Mass at birth (hereafter, birth mass) did not differ between herds, possibly because part of their winter ranges overlapped. However, Feuilles calves were smaller in autumn than George calves, possibly reflecting differences in summer ranges. The birth mass of calves also varied with year, likely as the outcome of both intrinsic and extrinsic factors. Birth and autumn body mass were influenced positively by habitat quality in June, estimated by the normalized difference vegetation index. The North Atlantic Oscillation of the previous winter was positively correlated with autumn mass of the George calves. Previous winter snowfall was negatively related to the mass of George calves, and daily movement rates in summer were negatively correlated with the mass of calves of both herds in autumn. Birth mass was positively related with productivity in October in the George herd and also with productivity 3 and 4 years later, which corresponds to the beginning of reproduction of females. We suggest that a mechanism of delayed quality effect of the calves could have been involved in the decrease of fall productivity and population size of the George herd.
Studies of site fidelity have been hampered by arbitrary designations of spatial scale and the lack of null models for comparison. We generated null expectations of fidelity at different scales from the distribution of radio-tracked animals in a population. We applied the models to space use of satellite-tracked caribou (Rangifer tarandus caribou), the most vagile nonvolant terrestrial animal, from populations representing sedentary and migratory ecotypes. We compared distances between consecutive-year locations of adult females to expectations based on the total range and seasonal range of each population. At the scale of the total range, sedentary and migratory caribou displayed remarkably similar philopatry, despite a 30-fold difference in size of their population ranges, from time of calving (late May) to breeding (late October). The most intense fidelity occurred during post-calving when, on average, sedentary and migratory females returned to as near as 6.7km and 123km, respectively, of locations occupied the previous year. At the scale of the seasonal range, the ecotypes differed. Sedentary caribou still displayed fidelity from calving to breeding; migratory caribou exhibited fidelity only during late autumn. For migratory, but not sedentary caribou, inter-year distances during winter were negatively correlated with age, implying that older females were more philopatric. We conclude that reproductive activities delimit the season of fidelity of female caribou of both ecotypes, and that scale-dependent ecotypic differences in fidelity may reflect different factors of population limitation. A spatially-explicit approach to site fidelity is essential for synthesizing patterns across studies.
To select their future breeding site, individuals usually have to assess local quality by using environmental cues. One optimal cue may be ‘public information’, the local reproductive success of conspecifics in a breeding patch (patch reproductive success) because it integrates the effect of all environmental factors on breeding success. However, the quality of information conveyed by patch reproductive success is likely to depend on (1) environmental predictability and (2) interactions between individuals. We investigated how these two factors, ignored by previous models, affect the performance of individuals using patch reproductive success for breeding habitat selection compared with other information. We built a two-patch, game-theoretical model to compare the success of a strategy of breeding habitat selection based on patch reproductive success relative to four other strategies: (1) random patch choice; (2) philopatry; (3) choice based on the presence of conspecifics the previous year (conspecific attraction); and (4) choice based on intrinsic patch quality the previous year. The results illustrate how the efficiency of strategies in tracking variations in patch quality depend on environmental predictability and costs linked to density dependence, themselves linked to the dynamics of spatial aggregation of individuals. In particular, strategies based on measures of patch reproductive success perform the best for intermediate and high temporal predictability of patch quality, whereas philopatry and conspecific attraction then perform poorly. The ‘conspecific attraction’ strategy always coexists with other strategies by efficiently parasitizing the information they use. We discuss the implications of a better understanding of breeding habitat selection behaviours for evolutionary and conservation biology. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Effective management and conservation of species, subspecies, or ecotypes require an understanding of how populations are structured in space. We used satellite-tracking locations and hierarchical and fuzzy clustering to quantify subpopulations within the behaviorally different barren-ground caribou (Rangifer tarandus groenlandicus), Dolphin and Union island caribou (R. t. groenlandicus x pearyi), and boreal (R. t. caribou) caribou ecotypes in the Northwest Territories and Nunavut, Canada. Using a novel approach, we verified that the previously recognized Cape Bathurst, Bluenose-West, Bluenose-East, Bathurst, Beverly, Qamanirjuaq, and Lorillard barren-ground subpopulations were robust and that the Queen Maude Gulf and Wager Bay barren-ground subpopulations were organized as individuals. Dolphin and Union island and boreal caribou formed one and two distinct subpopulation, respectively, and were organized as individuals. Robust subpopulations were structured by strong annual spatial affiliation among females; subpopulations organized as individuals were structured by migratory connectivity, barriers to movement, and/or habitat discontinuity. One barren-ground subpopulation used two calving grounds, and one calving ground was used by two barren-ground subpopulations, indicating that these caribou cannot be reliably assigned to subpopulations solely by calving-ground use. They should be classified by annual spatial affiliation among females. Annual-range size and path lengths varied significantly among ecotypes, including mountain woodland caribou (R. t. caribou), and reflected behavioral differences. An east-west cline in annual-range sizes and path lengths among migratory barren-ground subpopulations likely reflected differences in subpopulation size and habitat conditions and further supported the subpopulation structure identified.
Habitat selection and dispersal behaviour are key processes in evolutionary ecology. Recent studies have suggested that individuals may use the reproductive performance of conspecifics as a source of public information on breeding patch quality for dispersal decisions, but experimental evidence is still limited for species breeding in aggregates, i.e. colonial species. We addressed this issue by manipulating the local breeding success of marked individuals and that of their neighbours on a series of breeding patches of a colonial seabird, the black-legged kittiwake (Rissa tridactyla). Based on previous observations in this species, we predicted that individuals that lost their eggs on successful patches would attend their nest and come back to it the year after at a higher rate than individuals that lost their eggs on patches where their neighbours were also in failure. As predicted, the attendance of breeders and prospectors was strongly affected by the local level of breeding success, resulting in differential site fidelity and recruitment. This suggests that individuals used information conveyed by conspecific breeding performance to make decisions relative to breeding site selection. This process can amplify the response of these populations to environmental change and may have contributed to the evolution of colonial breeding.
Evidence for the fidelity of female barren-ground caribou (Rangifer tarandus spp.) of each herd to specific calving grounds is convincing. Involvement of learned behaviour in the annual return of those cows to the same calving grounds implies such actions are a form of «traditional» behaviour. Even wide variations in population size have not yet knowingly led to marked changes in size or location of calving grounds or prolonged abandonment of established ones. Rarely is the adoption of new calving grounds reported and emigration to another herd's calving ground or interchange between calving grounds has not yet been unequivocally documented. The calving experience of individual caribou and environmental pressures may modify the cow's use patterns of her calving grounds. The current definition of herds based on traditional calving grounds may require modification, if increasing caribou numbers result in changes in traditions. However, current data do not contradict either the fidelity to traditional calving grounds or the concept of herd identity based on that fidelity.
The Delta and Yanert caribou (Rangifer tarandus granti) herds apparently maintained discrete calving areas from 1979 through 1983 (as determined by radio telemetry studies), even though substantial intermixing occurred during other seasons. Also, the Delta herd apparently used a single traditional calving area from the 1950's through 1983, based on results of aerial surveys and 1979-83 telemetry studies. Calving distribution in 1984 changed dramatically; 5 of 25 radio-collared Delta herd cows ^3 years old and 5 of 24 radio-collared Delta herd cows <3 years old were located in the calving area of the Yanert herd, 72 km west-southwest of the traditional Delta herd calving area. Use of traditional, separate calving areas resumed for the two herds in 1985. One implication of these data is that the current definition of a caribou herd may not always apply. A second implication is that current models of caribou socioecology, based largely on the concepts of traditional use of calving grounds, herd identity/fidelity, and dispersal, inadequately predict or explain all empirical observations. An evolving model of optimal and dynamic use of space can help refine current models of caribou socioecology.
Sixty-four adult (2 + years) female caribou (Rangifer tarandus grand), radio-collared in April or May 1975 - 82, were relocated during the following June and/or July within the summer range of the Central Arctic Herd (CAH). Relocations made during the following three summers were used to assess range fidelity. Cumulative relocations of radio-collared females in the Central Arctic region were equivalent to 91% of the projected availability based on transmitter life. A chronological analysis indicates that 98%, 91%, and 82% of radio-collared females were found there one, two, and three years later; most of the progressively lower relocation success is probably attributable to transitter malfunctions rather than emigration. These observations suggest that summer range fidelity of adult females in the CAH is at least 90%, and may approach 100%.
A.T. Bergerud, Stuart Luttich, & Lodewijk Camps. “The Return of Caribou to Ungava.” McGill-Queen’s University Press, Montreal, Quebec. 586pp. ISBN 978-0-7735-3233-5.
Contradictory patterns of density-dependent animal dispersal can potentially be reconciled by integrating the conspecific attraction hypothesis with the traditional competition hypothesis. We propose a hypothesis that predicts a U-shaped relationship between density and both natal and breeding dispersal distance. Using 10 years of observations on a breeding colony of the Blue-footed Booby (Sula nebouxii), the hypothesis was confirmed by documenting simultaneous positive and negative density-dependent dispersal distances in natal and breeding dispersal of males and breeding dispersal of females within the colony. Point-pattern analyses demonstrated that the breeding sites of Blue-footed Boobies were highly aggregated in all years within a large study area, and aggregation presumably resulted in heterogeneity in patch density throughout the colony. As predicted, at moderate to high densities, dispersal distances showed positive density dependence, with individuals moving to lower density patches. In contrast, at low to moderate densities, dispersal distances showed negative density dependence, with individuals moving to higher density patches. In both sexes of the 1994 cohort, the higher the mean density in patches used by an individual over the long term (up to age 11 years), the fewer fledglings it produced. A positive effect of density on long-term reproductive success was not detected, possibly because birds that failed during pair formation or incubation were not sampled. Density of conspecifics may be an important influence on habitat selection of breeders, and dispersal may tend to carry individuals to patches where pair formation opportunities are better and negative effects of competition on reproductive success are reduced.
The Allee effect describes a scenario in which populations at low numbers are affected by a positive relationship between population growth rate and density, which increases their likelihood of extinction. The importance of this dynamic process in ecology has been under-appreciated and recent evidence now suggests that it might have an impact on the population dynamics of many plant and animal species. Studies of the causal mechanisms generating Allee effects in small populations could provide a key to understanding their dynamics.
To understand why population growth rate is sometimes positive and sometimes negative, ecologists have adopted two main approaches. The most common approach is through the density paradigm by plotting population growth rate against population density. The second approach is through the mechanistic paradigm by plotting population growth rate against the relevant ecological processes affecting the population. The density paradigm is applied a posteriori, works sometimes but not always and is remarkably useless in solving management problems or in providing an understanding of why populations change in size. The mechanistic paradigm investigates the factors that supposedly drive density changes and is identical to Caughley's declining population paradigm of conservation biology. The assumption that we can uncover invariant relationships between population growth rate and some other variables is an article of faith. Numerous commercial fishery applications have failed to find the invariant relationships between stock and recruitment that are predicted by the density paradigm. Environmental variation is the rule, and non-equilibrial dynamics should force us to look for the mechanisms of population change. If multiple factors determine changes in population density, there can be no predictability in either of these paradigms and we will become environmental historians rather than scientists with useful generalizations for the population problems of this century. Defining our questions clearly and adopting an experimental approach with crisp alternative hypotheses and adequate controls will be essential to building useful generalizations for solving the practical problems of population management in fisheries, wildlife and conservation.
Conspecific attraction is the preferential settlement into habitat patches with conspecifics. To be a good proximate strategy, fitness gains from settling with conspecifics must outweigh the costs of higher conspecific densities, such as intraspecific competition. Two types of benefits have been proposed to explain conspecific attraction: Allee effects (i.e., positive density dependence) and conspecific cueing (using conspecifics as an indicator of habitat quality). I present empirical evidence for conspecific attraction in the settlement of the porcelain crab, Petrolisthes cinctipes Randall (Anomura: Porcellanidae). Previous work demonstrated that P. cinctipes experiences strong intraspecific competition and that both Allee effects and conspecific cueing are present in P. cinctipes life-history. I developed an empirically-based fitness model of the costs and benefits of settling with conspecifics. Based on this model, I simulated optimal settlement to habitat patches that varied in conspecific density and habitat quality, where the correlation between density and habitat quality determined the level of conspecific cueing. I tested whether Allee effects alone, conspecific cueing alone, or Allee effects and conspecific cueing together could provide an ultimate explanation for the proximate settlement behavior of P. cinctipes. The settlement simulation was consistent with empirical settlement only when Allee effects and conspecific cueing were both included. Three life-history features are critical to this conclusion: (1) fitness is maximized at intermediate density, (2) fitness depends on the decisions of previous settlers, and (3) conspecific density provides good information about habitat quality. The quality of information garnered from conspecifics determines whether conspecific attraction is a good proximate strategy for settlement. I present a graphical illustration demonstrating how Allee effects and conspecific cueing work together to influence fitness, providing a conceptual framework for other systems.
The George River caribou herd increased from 15,000 animals in 1958 to 700,000 in 1988 - the largest herd in the world at the time. The authors trace the fluctuations in this caribou population back to the 1700s, detail how the herd escaped extinction in the 1950s, and consider current environmental threats to its survival. In an examination of the life history and population biology of the herd, The Return of Caribou to Ungava offers a synthesis of the basic biological traits of the caribou, a new hypothesis about why they migrate, and a comparison to herd populations in North America, Scandinavia, and Russia. The authors conclude that the old maxim, "Nobody knows the way of the caribou," is no longer valid. Based on a study in which the caribou were tracked by satellite across Ungava, they find that caribou are able to navigate, even in unfamiliar habitats, and to return to their calving ground, movement that is central to the caribou's cyclical migration. The Return of Caribou to Ungava also examines whether the herd can adapt to global warming and other changing environmental realities.
Knowledge of how predation risk affects population survivorship is important for understanding predator–prey relationships and designing effective conservation strategies. The Allee effect (inverse density dependence) can be generated when antipredator strategies become inefficient in small groups of prey, thus making the population more susceptible to catastrophic population collapse and extinction. Many populations of desert bighorn sheep (Ovis canadensis) are declining, and predation is, in many cases, a major mortality factor. We studied desert bighorns at the Red Rock Wildlife Area, New Mexico, USA, to assess predation risk in different group types (ram, ewe, mixed) and age–sex classes. Multiple regression analysis revealed that predation risk (as estimated by individual vigilance) increased with smaller group size and greater inter-individual distance for all bighorns, with groups of <5 individuals subject to the greatest risk. Although rugged terrain is thought to provide refuge from predators, habitat ruggedness did not influence vigilance. The biggest males in ram groups experienced the greatest predation risk in that they were in the smallest groups, were most likely to be solitary, and were spaced farther apart from conspecifics. Although big rams spent twice as much time vigilant as other age–sex classes, collective alertness was lowest for ram groups. The conclusion that big rams were most at risk from predation was partially supported by the recent predation history of the population and previous studies in which mountain lion (Felis concolor) kills were biased toward rams. We discuss the management implications of these results for small populations subject to Allee effects, including reintroduction and/or translocation practices and selective removal of problem predators. We suggest that the use of multivariate techniques to simultaneously explore the influence of multiple factors and the use of vigilance as a correlate of predation risk would be useful management tools for assessing seasonal and class-specific vulnerability to predation.
A large barren-ground caribou (Rangifer tarandus granti) population (the Bering Seacoast Herd) historically ranged across southwest Alaska. The size of this herd peaked in the early 1860s but declined by the late 1880s. Caribou numbers remained low in southwest Alaska for the next 100 years. Biologists have argued that periodic dispersal has been an important factor in caribou population dynamics. However, others conclude there was no credible evidence that significant interchange between herds has ever occurred in Alaska. Since 1981, we monitored 318 radiocollared caribou and documented dramatic population growth, erratic movements, shifts from traditional ranges, and changes in migratory behavior. We also documented shifts in calving distribution that may contrast with conventional concepts of calving tradition and herd identity. Some biologists have concluded caribou herds can be considered closed populations for management purposes because the number of dispersing caribou is so small that it has no influence on population dynamics. We propose that the current definition of a herd may be appropriate for short-term management; however, over long time frames and large spatial scales, metapopulations may better describe caribou ecology and be more useful in long-term caribou conservation.
1 Changes in demography and studies on physical condition of the Riviere George caribou Rangifer tarandus herd have suggested that its size may be primarily regulated by the amount of forage available on the summer range. 2 We therefore document the impact of grazing and trampling on composition and productivity of two plant communities, the shrub tundra and stands of dwarf birch, within this range, Ungrazed sites were rare, but four previously located small areas were used as control sites. 3 For the shrub tundra, the lichen mat was absent in grazed sites and ground previously occupied by lichens was either bare, covered by fragments of dead lichens and mosses or recolonized by early succession lichen species. Ground cover of shrubs not eaten by caribou was lower in grazed sites than in ungrazed sites, and coverage of graminoids, forage shrubs and forbs did not differ significantly between grazed and ungrazed sites. 4 In stands of dwarf birch grazed by caribou, ground cover and leaf biomass of Betula glandulosa was significantly lower than in ungrazed sites. 5 Productivity of forage plant species over the summer range was estimated at 22.5 g m(-2) year(-1) in an ungrazed condition compared to 10.3 g m(-2) year(-1) when grazed. 6 At the landscape level, caribou have fragmented the distribution of their food resource by reducing biomass of shrub tundra and stands of dwarf birch to a very low level. 7 The serious negative impact of migratory ungulates on plant productivity of their summer range may be explained by characteristics of the vegetation and the high carrying capacity of winter compared to summer ranges. Significant factors related to the vegetation are its low resilience and productivity and the absence of a response of vascular plants following removal of lichens.
Warder C. Allee brought attention to the possibility of a positive relationship between aspects of fitness and population size 50 years ago. Until recently, however, this concept was generally regarded as an intriguing but relatively unimportant aspect of population ecology. Increasing appreciation that Allee effects must be incorporated into models of population dynamics and habitat use, together with recent interest in the implications of sociality for conservation, have shown that for ecology and conservation the consequences of the Allee effect are profound. The Allee effect can be regarded not only as a suite of problems associated with rarity, but also as the basis of animal sociality.
Many animals benefit from the presence of conspecifics by reducing their rate of scanning for predators while increasing their time spent foraging. This group size effect could arise from a decreased perception of individual risk (dilution hypothesis) and/or an increased ability to detect predators (detection hypothesis). We compared individual and group vigilance of Rocky Mountain elk, Cervus elaphus, in three regions of Yellowstone National Park, Wyoming, U.S.A. that varied in their encounter frequency with coyote, Canis latrans, grizzly bear, Ursus arctos, and grey wolf,Canis lupus , predators. Adult females without calves increased scanning and decreased foraging with high encounter risk and small herd size. Adult females with calves increased scanning and decreased foraging with high encounter risk, but showed no decrease in scanning with large herd size. Yearlings increased scanning and decreased feeding with small herd size, but not with high encounter risk. Adult males were least vigilant, fed most and were not influenced by encounter risk or herd size. These age–sex class differences led to significant differences in group vigilance depending on the composition of the herd. Herds with a majority of mothers were significantly more vigilant than herds with a majority of adult males. However, these differences in group vigilance had no influence on the individual scanning of females without calves. Thus, the decrease in individual scanning with herd size may depend more on changes in individual risk than on cooperative detection of predators. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
Public information, i.e. local reproductive performance of conspecifics, is expected to be a highly valuable cue for breeding habitat selection. However, the access to this cue may be spatially and temporally constrained. When public information is unavailable, individuals may use other integrative cues, such as the local density of breeders.
Departure decisions of collared flycatchers ( Ficedula albicollis ) were shown previously to be related to both public information and breeding density, in a long‐term correlative study of a fragmented population. Here, we tested whether flycatchers also use public information (number and condition of fledglings produced locally) and breeding density to make individual settlement decisions in the following year.
Immigration rates were computed to measure the degree of attractiveness of patches to new breeders. We investigated the relative influence of public information and breeding density on immigration rates of yearlings and older adults separately. The access to public information for settlement decisions may indeed be more limited for yearlings.
Immigration rate in a patch increased with mean fledgling number in the previous year for older adults but not for yearlings. Yearling immigration rate was correlated positively to mean fledgling condition when patch breeding density in the previous year was low, but negatively when density was high.
Immigration rates of both yearlings and older adults increased with breeding density in the previous year. Breeding density explained a larger part of the variance in immigration rate than patch reproductive success.
The proportion of yearlings among breeders decreased with increasing patch reproductive success and breeding density in the previous year, suggesting that local competition was high in attractive patches.
Our results thus suggest that public information is also used for immigration decisions. However, decisions of yearlings are more complex than those of older adults, due to their more limited access to public information and the higher impact of intraspecific competition. Conversely, all individuals seemed to cue on breeding density in a similar way. Density is correlated to patch reproductive success, and may be a more easily accessible cue. We discuss the potential advantages of using conspecific density over conspecific reproductive performance for future immigration decisions.
Allee effects can have significant consequences for small populations and understanding the causal mechanisms for such effects is important for guiding conservation actions. One proposed mechanism is through predation, in which a type II functional response leads to increasing predation rates as prey numbers decline. However, models to support this mechanism have incorporated only a single declining prey species in the functional response, which is probably an oversimplification. We reevaluated the potential for predator-mediated Allee effects in a multi-prey system using Holling's disc equation. We also used empirical data on a large herbivore to examine how grouping behavior may influence the potential for predation-mediated Allee effects. Results based on a multi-prey expression of the functional response predict that Allee effects caused by predation on relatively rare secondary prey may not occur because handling time of the abundant prey dominates the functional response such that secondary prey are largely "bycatch". However, a predator-mediated Allee effect can occur if secondary prey live in groups and if, as the population declines, their average group size declines (a relationship seen in several species). In such a case, the rate at which the number of groups declines is less than the rate at which the population declines. Thus the rate at which a predator encounters a group remains relatively stable, but when a predator kills one animal from smaller groups, the predation rate increases. These results highlight the need to evaluate risks associated with potential changes in group size as populations decline.
Photocopy. Ann Arbor, Michigan : University Microfilms International, 1977. Thesis--University of California, Berkeley. Bibliography: p. 663-699.
Cover title. Thesis--University of California, Berkeley. Includes bibliographical references (p. 663-699).
We studied the distribution and faecal shedding pattern of the first-stage larvae (L1) of Elaphostrongylus cervi (Nematoda: Protostrongylidae) in the red deer (Cervus elaphus) across Spain, where excretion was widespread. We evaluated the effects of individual, population and environmental factors on E. cervi L1 counts in 18 free-ranging red deer populations in South Central Spain. In this area, prevalence was 71.42+/-2.14% (n = 448) and mean intensity (n = 320) was 74.50+/-10.35. Aggregation of deer at water-holes was positively associated with E. cervi L1 prevalence, possibly due to spatial and temporal odds of infected gastropods, red deer and infective E. cervi L1 larvae being encountered. Prevalence increased with age, and there was also a trend towards males having higher intensities than females. A slightly decreasing age-intensity profile was identified for females, which may suggest a role of acquired immunity.
Genetic differentiation is generally assumed to be low in highly mobile species, but this simplistic view may obscure the complex conditions and mechanisms allowing genetic exchanges between specific populations. Here, we combined data from satellite-tracked migratory caribou (Rangifer tarandus), microsatellite markers, and demographic simulations to investigate gene flow mechanisms between seven caribou herds of eastern Canada. Our study included one montane, two migratory, and four sedentary herds. Satellite-tracking data indicated possibilities of high gene flow between migratory herds: overlap of their rutting ranges averaged 10% across years and 9.4% of females switched calving sites at least once in their lifetime. Some migratory individuals moved into the range of the sedentary herds, suggesting possibilities of gene flow between these herds. Genetic differentiation between herds was weak but significant (FST=0.015): migratory and montane herds were not significantly distinct (FST all<or=0.005), whereas sedentary herds were more differentiated (FST=0.018-0.048). Geographical distances among sedentary herds limited gene flow. Historical estimates of gene flow were higher from migratory herds into sedentary herds (4Nm all>9) than vice-versa (4Nm all<5), which suggests migratory herds had a demographic impact on sedentary herds. Demographic simulations showed that an effective immigration rate of 0.0005 was sufficient to obtain the empirical FST of 0.015, while a null immigration rate increased the simulated FST to >0.6. In conclusion, the weak genetic differentiation between herds cannot be obtained without some genetic exchanges among herds, as demonstrated by genetic and spatial data.
Towards the development of a policy on the management of human activities in caribou calving and post-calving grounds. Contract # 00-0210 for Department of Indian Affairs and Northern Development
- F H Weihs
- P J Usher
Weihs, F.H. & Usher, P.J. 2001. Towards the development
of a policy on the management of human activities in caribou
calving and post-calving grounds. Contract # 00-0210 for
Department of Indian Affairs and Northern Development, Ottawa.
- G M Carroll
- L S Parrett
- J C George
- D A Yokel
Carroll, G.M., Parrett, L.S., George, J.C., & Yokel,
D.A.. 2005. Calving distribution of the Teshekpuk caribou herd, 1994-2003. – Rangifer Special Issue No. 16:
27-35.
Empirical and theoretical considerations toward a model for caribou socio-ecology
- J L Davis
- P Valkenburg
- R D Beortje
Davis, J.L., Valkenburg, P., & Beortje, R.D. 1986. Empirical and theoretical considerations toward a model for
caribou socio-ecology. -Rangifer 1: 151-159.
Surveys of the Beverly caribou calving grounds, 1957-1994. Northwest Territories Department of Resources, Wildlife and Economic Development
- A Gunn
- M Sutherland
Gunn, A. & Sutherland, M. 1997. Surveys of the Beverly
caribou calving grounds, 1957-1994. Northwest Territories Department of Resources, Wildlife and Economic
Development. File Rep. No. 120. 119pp.
Assessment of caribou protection measures. Unpubl. report submitted to Indian and Northern Affairs Canada
- A Gunn
- K G Poole
- J Wierzchowski
- M Campbell
Gunn, A., Poole, K.G., Wierzchowski, J., & Campbell,
M. 2007. Assessment of caribou protection measures. Unpubl.
report submitted to Indian and Northern Affairs Canada, Gatineau, Québec. 45pp.
A geostatistical analysis for the patterns of caribou occupancy on the Bathurst calving grounds 1966-2007. Unpubl. report submitted to Indian and Northern Affairs Canada, Yellowknife
- A Gunn
- K G Poole
- J Wierzchowski
Gunn, A., Poole, K.G., & Wierzchowski, J. 2008. A
geostatistical analysis for the patterns of caribou occupancy on
the Bathurst calving grounds 1966-2007. Unpubl. report
submitted to Indian and Northern Affairs Canada, Yellowknife, NWT. 51pp.
Beverly herd of barren-ground caribou: calving ground survey
- D Johnson
- A Gunn
- J Nagy
- J Williams
Johnson, D., Gunn, A., Nagy, J., & Williams, J. In Press.
Beverly herd of barren-ground caribou: calving ground survey,
June 2007. Northwest Territories Department of Environment and Natural Resources, Manuscript Report.
Research fi nal report. Alaska Department of Fish and Game, Division of Wildlife
- J W Lieb
- W B Cella
- R W Tobey
Lieb, J. W., Cella, W.B., & Tobey, R.W. 1994. Population dynamics of the Mentasta caribou herd. Research fi nal
report. Alaska Department of Fish and Game, Division
of Wildlife, Juneau, Alaska. 72pp.
In press. An estimate of breeding females in the Bathurst herd of barren-ground caribou
- J S Nishi
- B Croft
- J Bolanger
- J Adamczewski
Nishi, J.S., Croft, B., Bolanger, J., & Adamczewski, J.
In press. An estimate of breeding females in the Bathurst herd
of barren-ground caribou, June 2009. Northwest Territories Department of Environment and Natural Resources,
File Report.