scholarly journals The role of predation in the decline and extirpation of woodland caribou

2020 ◽  
Author(s):  
Heiko Wittmer ◽  
ARE Sinclair ◽  
BN McLellan
Keyword(s):  
Rangifer Tarandus ◽  
Population Decline ◽  
Temporal Distribution ◽  
Pregnancy Rates ◽  
Foraging Habitat ◽  
Woodland Caribou ◽  
Instantaneous Rate ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Winter Foraging

To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from <5 to >500 individuals. Our results showed that the rates of increase of these subpopulations varied from -0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% ±2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories. © Springer-Verlag 2005.

scholarly journals The role of predation in the decline and extirpation of woodland caribou

2020 ◽  
Author(s):  
Heiko Wittmer ◽  
ARE Sinclair ◽  
BN McLellan
Keyword(s):  
Rangifer Tarandus ◽  
Population Decline ◽  
Temporal Distribution ◽  
Pregnancy Rates ◽  
Foraging Habitat ◽  
Woodland Caribou ◽  
Instantaneous Rate ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Winter Foraging

To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from <5 to >500 individuals. Our results showed that the rates of increase of these subpopulations varied from -0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% ±2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories. © Springer-Verlag 2005.

scholarly journals Population dynamics of the endangered mountain ecotype of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada

2020 ◽  
Author(s):  
Heiko Wittmer ◽  
BN McLellan ◽  
DR Seip ◽  
JA Young ◽  
TA Kinley ◽  
...  
Keyword(s):  
British Columbia ◽  
Population Dynamics ◽  
Rangifer Tarandus ◽  
Population Decline ◽  
Survival Rates ◽  
Adult Survival ◽  
Rangifer Tarandus Caribou ◽  
Vital Rates ◽  
Woodland Caribou ◽  
Annual Survival

We used census results and radiotelemetry locations of >380 collared individuals sampled over the entire distribution of the endangered mountain ecotype of woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)) in British Columbia, Canada, to delineate population structure and document the size and trend of the identified populations. We also describe the spatial pattern of decline and the causes and timing of adult mortality and provide estimates of vital rates necessary to develop a population viability analysis. Our results indicate that the abundance of mountain caribou in British Columbia is declining. We found adult female annual survival rates below annual survival rates commonly reported for large ungulates. The major proximate cause of population decline appears to be predation on adult caribou. Spatial patterns of population dynamics revealed a continuous range contraction and an increasing fragmentation of mountain caribou into smaller, isolated subpopulations. The population fragmentation process predominantly occurs at the outer boundaries of the current distribution. Our results indicate that recovery strategies for mountain caribou should be directed at factors contributing to the fragmentation and isolation of mountain caribou populations as well as management strategies aimed at increasing adult survival. © 2005 NRC Canada.

Woodland caribou: Facts for forest managers

1992 ◽  
Vol 68 (4) ◽  
pp. 481-491 ◽  
Author(s):  
H. G. Cumming
Keyword(s):  
Forest Management ◽  
Rangifer Tarandus ◽  
Population Decline ◽  
Habitat Destruction ◽  
Rangifer Tarandus Caribou ◽  
Woodland Caribou ◽  
Mortality Factors ◽  
Resource Managers ◽  
Ultimate Cause ◽  
Multiple Resource

A literature review points to predation as the proximate factor controlling woodland caribou (Rangifer tarandus caribou) populations in most cases, but that finding does not obviate the need for caribou to be included in forest management. Managers must consider the indirect effects of forest operations on caribou through their impacts on caribou mortality factors, such as prédation. Lichens remain important. Habitat destruction may in some cases be the ultimate cause of population decline. Reactions of caribou to disturbance vary, and remain controversial; more research is needed. Multiple resource managers of boreal commercial forests should identify sensitive components of caribou range – calving grounds, rutting locations, wintering areas, and travel routes among them – and prescribe for these areas in forest management plans. Ways of accommodating caribou in commercial forests are not well established, but some examples suggest how this might be done. Most importantly, areas that have been proven by their continued use to contain all necessary requirements for caribou survival should not be physically altered until their essential qualities and functions are better understood. Key words: Rangifer tarandus caribou, woodland caribou, predation, forest management.

An experimental study of declining populations

2005 ◽  
Vol 32 (6) ◽  
pp. 481 ◽  
Author(s):  
Jim Hone ◽  
the late Graeme Caughley ◽  
David Grice
Keyword(s):  
Experimental Study ◽  
Population Decline ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Second Phase ◽  
Population Declines ◽  
Negative Effects ◽  
Instantaneous Rate ◽  
Rate Of Increase ◽  
Declining Populations

Wildlife population declines have been attributed to predation, habitat change, and other agents of decline. An experimental study applied predation (at three levels) and habitat (at two levels) treatments over two years and measured the patterns of decline of populations of a medium-sized mammal (European rabbits). A model of population dynamics and effects of the treatments predicted negative effects of both treatments and an interaction of the treatments. All populations declined during the study including the experimental controls. During the first seven months (first phase of the study) the rate of decline, as estimated by the observed monthly instantaneous rate of increase (r), was more negative (P < 0.05) with increasing predation levels but there was no effect (P > 0.05) of habitat manipulation on r. There were no significant effects of treatments on rabbit abundance, or density, during the first phase of the study. During the second phase of the study, of 12 months’ duration, there were no significant (P > 0.05) effects of treatments on rabbit abundance, density, or r. There were no significant (P > 0.05) interactions of treatments on any response variable during either phase of the study. The interaction predicted by the theoretical model was not supported. Estimated abundance at the end of the study was not related (P > 0.05) to initial abundance (correlation = 0.023). The implications of the results are that such experimental studies can be used to evaluate theoretical models, though such studies may require a larger number of treatment replicates, and treatments at more extreme levels, to more clearly detect the effects of agents of population decline and their interactions.

scholarly journals Effects of spirodiclofen on the reproductive potential of two-spotted spider mite (Acari: Tetranychidae) ovipositing females

2009 ◽  
Vol 61 (4) ◽  
pp. 777-785 ◽  
Author(s):  
D. Marcic ◽  
Irena Ogurlic ◽  
P. Peric
Keyword(s):  
Spider Mite ◽  
Population Decline ◽  
Survival Rates ◽  
Reproductive Potential ◽  
Adult Emergence ◽  
Egg Laying ◽  
Instantaneous Rate ◽  
Rate Of Increase ◽  
Survival And Reproduction ◽  
Two Spotted Spider Mite

A laboratory bioassay was conducted to evaluate the effects of spirodiclofen on the survival and reproduction of young and mated females of two-spotted spider mite (Tetranychus urticae Koch). The females were sprayed with a series of acaricide concentrations (96, 48, 24, 12, and 6 mg/l) 24-30 h after adult emergence, i.e., at the age most likely to exhibit dispersal behavior and close to their reproductive maximum. The proportions of T. urticae females that survived treatment without symptoms of poisoning were concentration-dependent, ranging between 0.41 and 0.88 (0.96 in the control). With the exception of females that survived 6 mg/l, fecundity of the treated female mites was strongly affected during the exposure, compared to the control. The mean daily fecundity (EL) and mean daily fertility (EH) of surviving females, transferred daily to new leaf disks over the following five days, significantly decreased as spirodiclofen concentrations increased. In treatments with 6 mg/l and 12 mg/l, only the latter concentration significantly reduced both EL and EH, compared to the control. In females that survived 24 mg/l and 48 mg/l, these life history parameters were reduced by over 90%, while treatment with 96 mg/l completely terminated egg-laying. The treated females lived for a significantly shorter time than untreated ones, with the exception of females that survived 6 mg/l. Compared to the control females, gross fecundity (GL) and gross fertility (GH) of the treated females were strongly reduced on the first and second day; from the third day onward, females treated with the lowest concentrations achieved marked recovery, their GL and GH going even above the values in the control. However, net fecundity (NL) and net fertility (NH) of all treated females decreased considerably throughout the trial, indicating that survival rates of these females were lower, compared to the control. Calculated as total sums of gross and net daily schedules within five days, fecundity and fertility significantly decreased as spirodiclofen concentration increased. The two lowest concentrations failed to achieve a significant reduction of GL, while GH, NL, and NH were significantly lower than control values starting with the females treated with 6 mg/L. A high percentage of unhatched eggs, especially during the initial two days after treatment (35-100%), further contributed to the significant reduction in fertility of the females treated with spirodiclofen. All concentrations of spirodiclofen significantly reduced the instantaneous rate of increase. Regression analysis showed a linear population decline with increased acaricide concentrations (y = 1.13 - 0.24x; R2 = 0.91, p < 0.05).

scholarly journals Population dynamics of the endangered mountain ecotype of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada

2020 ◽  
Author(s):  
Heiko Wittmer ◽  
BN McLellan ◽  
DR Seip ◽  
JA Young ◽  
TA Kinley ◽  
...  
Keyword(s):  
British Columbia ◽  
Population Dynamics ◽  
Rangifer Tarandus ◽  
Population Decline ◽  
Survival Rates ◽  
Adult Survival ◽  
Rangifer Tarandus Caribou ◽  
Vital Rates ◽  
Woodland Caribou ◽  
Annual Survival

We used census results and radiotelemetry locations of >380 collared individuals sampled over the entire distribution of the endangered mountain ecotype of woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)) in British Columbia, Canada, to delineate population structure and document the size and trend of the identified populations. We also describe the spatial pattern of decline and the causes and timing of adult mortality and provide estimates of vital rates necessary to develop a population viability analysis. Our results indicate that the abundance of mountain caribou in British Columbia is declining. We found adult female annual survival rates below annual survival rates commonly reported for large ungulates. The major proximate cause of population decline appears to be predation on adult caribou. Spatial patterns of population dynamics revealed a continuous range contraction and an increasing fragmentation of mountain caribou into smaller, isolated subpopulations. The population fragmentation process predominantly occurs at the outer boundaries of the current distribution. Our results indicate that recovery strategies for mountain caribou should be directed at factors contributing to the fragmentation and isolation of mountain caribou populations as well as management strategies aimed at increasing adult survival. © 2005 NRC Canada.

scholarly journals Population dynamics of the endangered mountain ecotype of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada

2005 ◽  
Vol 83 (3) ◽  
pp. 407-418 ◽  
Author(s):  
Heiko U Wittmer ◽  
Bruce N McLellan ◽  
Dale R Seip ◽  
James A Young ◽  
Trevor A Kinley ◽  
...  
Keyword(s):  
British Columbia ◽  
Population Dynamics ◽  
Rangifer Tarandus ◽  
Population Decline ◽  
Survival Rates ◽  
Adult Survival ◽  
Rangifer Tarandus Caribou ◽  
Vital Rates ◽  
Woodland Caribou ◽  
Annual Survival

We used census results and radiotelemetry locations of >380 collared individuals sampled over the entire distribution of the endangered mountain ecotype of woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)) in British Columbia, Canada, to delineate population structure and document the size and trend of the identified populations. We also describe the spatial pattern of decline and the causes and timing of adult mortality and provide estimates of vital rates necessary to develop a population viability analysis. Our results indicate that the abundance of mountain caribou in British Columbia is declining. We found adult female annual survival rates below annual survival rates commonly reported for large ungulates. The major proximate cause of population decline appears to be predation on adult caribou. Spatial patterns of population dynamics revealed a continuous range contraction and an increasing fragmentation of mountain caribou into smaller, isolated subpopulations. The population fragmentation process predominantly occurs at the outer boundaries of the current distribution. Our results indicate that recovery strategies for mountain caribou should be directed at factors contributing to the fragmentation and isolation of mountain caribou populations as well as management strategies aimed at increasing adult survival.

scholarly journals Woodland caribou population decline in Alberta: fact or fiction?

Rangifer ◽  
1996 ◽  
Vol 16 (4) ◽  
pp. 223 ◽  
Author(s):  
Corey J.A. Bradshaw ◽  
Daryll M. Hebert
Keyword(s):  
Wildlife Management ◽  
Canis Lupus ◽  
Rangifer Tarandus ◽  
Population Decline ◽  
Population Fluctuations ◽  
Woodland Caribou ◽  
Subsistence Hunting ◽  
The Past ◽  
Adequate Information ◽  
Aboriginal Subsistence

We re-assessed the view of a major woodland caribou (Rangifer tarandus caribou) population decline in Alberta. Several historical publications and provincial documents refer to this drastic decline as the major premise for the designation of Alberta's woodland caribou an endangered species. In the past, wildlife management and inventory techniques were speculative and limited by a lack of technology, access and funding. The accepted trend of the decline is based on many speculations, opinions and misinterpretation of data and is unsubstantiated. Many aerial surveys failed to reduce variance and did not estimate sightability. Most surveys have underestimated numbers and contributed unreliable data to support a decline. Through forest fire protection and the presence of extensive wetlands, the majority of potential caribou habitat still exists. Recreational and aboriginal subsistence hunting does not appear to have contributed greatly to mortality, although data are insufficient for reliable conclusions. Wolf (Canis lupus), population fluctuations are inconclusive and do not provide adequate information on which to base prey population trends. The incidence of documented infection by parasites in Alberta is low and likely unimportant as a cause of the proposed decline.

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