scholarly journals Modeling the decline of the Porcupine Caribou Herd, 1989-1998: the importance of survival vs. recruitment

Rangifer ◽  
2003 ◽  
Vol 23 (5) ◽  
pp. 123
Author(s):  
Stephen M. Arthur ◽  
Kenneth R. Whitten ◽  
Francis J. Mauer ◽  
Dorothy Cooley
Keyword(s):  
Population Growth ◽  
Population Size ◽  
Rangifer Tarandus ◽  
Deterministic Model ◽  
Survival Rates ◽  
Adult Survival ◽  
Population Changes ◽  
Temporary Reduction

The Porcupine caribou (Rangifer tarandus granti) herd increased from approximately 100 000 animals during the 1970s to 178 000 in 1989, then declined to 129 000 by 1998. Our objective was to model the dynamics of this herd and investigate the potential that lower calf recruitment, as was observed during 1991-1993, produced the observed population changes. A deterministic model was prepared using estimates of birth and survival rates that reproduced the pattern of population growth from 1971-1989. Then, parameters were changed to simulate effects of lower calf recruitment and adult survival. Reducing recruitment for 3 years caused an immediate reduction in population size, but the population began to recover in 5-6 years. Even a dramatic temporary reduction in recruitment did not explain the continuing decline after 1995. In contrast, a slight but persistent reduction in adult survival caused a decline that closely followed the observed pattern. This suggests that survival of adults, and perhaps calves, has declined since the late 1980s.

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.

Use of Pup Counts in Indexing Population Changes in Pinnipeds

1985 ◽  
Vol 42 (5) ◽  
pp. 873-879 ◽  
Author(s):  
J. M. Berkson ◽  
D. P. DeMaster
Keyword(s):  
Life History ◽  
Population Growth ◽  
Maximum Rate ◽  
Population Change ◽  
Adult Survival ◽  
Population Changes ◽  
Feedback Mechanisms ◽  
Density Dependent ◽  
Life History Parameters ◽  
Pup Survival

A series of population simulations were used to test the accuracy of estimating the discrete rates of population change (RPC) from annual pup counts. The simulations indicate that pup counts can give a biased estimate of RPC, and that the magnitude and direction of bias depends on which life history parameters are density dependent and on the maximum rate of population change. In general, if pre-census pup survival is density dependent the estimated RPC using pup counts is too low. If post-census pup survival is density dependent, the estimated RPC is too high. If adult survival is density dependent, there is very little bias in the estimate. The results indicate that pup counts can be reliable indicators of population growth, but caution should be used in interpreting the results unless density feedback mechanisms have been identified.

Age distribution of breeding female Antarctic fur seals in relation to changes in population growth rate

1990 ◽  
Vol 68 (10) ◽  
pp. 2209-2213 ◽  
Author(s):  
I. L. Boyd ◽  
N. J. Lunn ◽  
P. Rothery ◽  
J. P. Croxall
Keyword(s):  
Population Growth ◽  
Survival Rates ◽  
Age Distribution ◽  
Adult Survival ◽  
South Georgia ◽  
Breeding Female ◽  
Fur Seals ◽  
Rate Of Increase ◽  
The Mean ◽  
Antarctic Fur Seals

The age distribution of breeding female Antarctic fur seals at Bird Island, South Georgia, in 1988 was compared with the age distribution of a sample obtained in 1971–1973. The mean age in 1971–1973 was 7.41 (SE = 0.26) years and in 1988 it was 6.93 (SE = 0.20) years. After correction for age-dependent arrival time at the pupping beach in 1988, the mean age was 6.22 (SE = 0.14 years), which was significantly lower than in 1971–1973. Indicators of population size suggested that population growth at Bird Island had declined to below 3% annually by 1988 compared with rapid growth (17%) in 1958–1972. Exponential models fitted to the frequency distribution of age-classes greater than age 5 years and corrected for the rate of increase of the population gave adult survival rates of 0.66 (SE = 0.03) and 0.88 (SE = 0.02) for the 1988 and 1971–1973 samples, respectively. The reduced apparent adult survival rate in the 1988 sample was probably caused by emigration brought about by high densities of females on the pupping beaches. There are few signs from this analysis that the fur seal population at South Georgia is close to carrying capacity.

Sensitivity and elasticity analysis of Tetranychus urticae Koch population parameters: Consequences for pest management 

2020 ◽  
Vol 25 (2) ◽  
pp. 268-284
Author(s):  
Alireza Nemati ◽  
Elham Riahi ◽  
Saadollah Houshmand
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Matrix Models ◽  
Survival Rates ◽  
Demographic Variables ◽  
Adult Survival ◽  
Egg Survival ◽  
Horticultural Crops ◽  
Structured Matrix ◽  
Different Temperatures

Sensitivity and elasticity analyses quantify the effect of an absolute and proportional change in demographic variables on population growth rate (λ), respectively. The methods are used to identify the variable(s) that have the largest influence on λ. Tetranychus urticae Koch is one of the most polyphagous tetranychid mites which has been collected from plenty plant species including agricultural and horticultural crops. In this study, sensitivity and elasticity analyses were used to investigate the effects of various demographic variables on λ at five different temperatures (15, 20, 25, 30 and 35 °C), using both age- and stage-structured matrix models. Considering the sensitivity of λ to age-dependent fecundity rates (fx), it was found that starting oviposition one day earlier was associated with the highest sensitivity compared to the other age classes, irrespective of temperature. Besides, results from both age- and stage-structured matrix models indicated that λ is more sensitive to changes in survival rates than in fecundity rates at all temperatures. Furthermore, female individuals at the ages of 46, 23, 14, 11 and 7 days had the highest contribution to population growth in comparison with other ages, when reared at the above-mentioned temperatures, respectively. Also, the sensitivity of λ to the changes in survival of adults was higher than in other stages. Besides, the elasticity to fecundity rate at the age of first reproduction was considerably higher than those associated with the age of last reproduction. The survival rates (si) generally exhibited a higher elasticity than the transition rates (gi). Overall, adult survival had the highest influence on λ followed by immature survival, egg survival, and female fecundity. Consequently, management efforts that aim at decreasing adult survival are likely to yield the best results with regard to reducing the growth rate of T. urticae.

Population dynamics of the black-cheeked gnateater (Conopophaga melanops, Conopophagidae) in southern Brazil

2009 ◽  
Vol 25 (6) ◽  
pp. 605-613 ◽  
Author(s):  
André Magnani Xavier de Lima ◽  
James Joseph Roper
Keyword(s):  
Population Dynamics ◽  
Population Growth ◽  
Breeding Season ◽  
Survival Rates ◽  
Territory Size ◽  
Adult Survival ◽  
Southern Brazil ◽  
Annual Survival ◽  
Socially Monogamous ◽  
Population Structure And Dynamics

Abstract:Population structure and dynamics of the black-cheeked gnateater (Conopophaga melanops) were studied at Salto Morato Nature Reserve, in Paraná, southern Brazil, from October 2006 to September 2007. Territory size and population density, breeding season (timing and length), reproductive success and annual survival rates were estimated from sightings of 18 marked adult birds and the success of 18 nesting attempts. The black-cheeked gnateater is socially monogamous and territorial, with a breeding-season length of approximately 3 mo beginning in early October. Predation caused most nest failures, nest survival was 0.96 d−1and apparent annual nesting success was 22%, resulting in annual productivity of 0.36 individuals per adult. Apparent adult annual survival was ~0.44 y−1. Seventy-five per cent of fledglings survived at least 2 mo after fledging. Two methods of estimating population growth rate suggest very different rates: r = −0.04 (~ stable), or λ varies between 0.475–0.616 (declining). Yet, low apparent adult survival suggests that territories are not permanent, perhaps abandoned after nest failure. We find that by estimating population growth, even in short-term studies, testable hypotheses can be generated that will allow better understanding of population dynamics.

scholarly journals Reef manta ray life history and demography: is it really all about survival?

2016 ◽  
Author(s):  
Isabel M Smallegange ◽  
Isabelle BC van der Ouderaa ◽  
Yara Tibiriçá
Keyword(s):  
Growth Rate ◽  
Survival Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Survival Rates ◽  
Adult Survival ◽  
Lifetime Reproductive Success ◽  
Annual Survival ◽  
Manta Ray ◽  
Reef Manta Ray

Background. The trade in gill plates of devil and manta rays has increased greatly over the last two decades. The resulting increased mortality, in addition to mortality caused by by-catch, means that many ray populations are declining in size. The aim of this study was to ascertain the main demographic drivers of population change in reef manta rays (Manta alfredi) to increase our understanding of their demography and hence provide insight into potential conservation measures. Methods. We developed a population projection model for reef manta rays and used published life history data to parameterise the model and also used these data as points of reference to compare our model output to. Because little is known about yearling and juvenile survival of reef manta rays, we conducted our analyses across a range of plausible survival rate values of yearlings, juveniles, and also adults. Results. The model accurately captured observed patterns of variation in population growth rate, lifetime reproductive success and cohort generation time for different reef manta ray populations around the world. Varying the survival rates of the different life stages revealed that increasing adult annual survival rate always positively and additively affected population growth rate, lifetime reproductive success and cohort generation time. Variation in yearling and juvenile annual survival rate, however, had different and varying effects on the latter three population descriptors, highlighting the importance of obtaining accurate estimates of these survival rates from natural populations. Our elasticity analysis revealed that for both declining and stable populations, the population growth rate is most sensitive to changes in either juvenile or adult survival rate, depending on yearling and adult annual survival rate values. Discussion. Many reef manta ray populations are declining, resulting in local extinction unless effective conservation measures are taken. Based on our detailed demographic analysis, we suggest that reef manta ray conservation would particularly benefit from focusing on increasing juvenile and adult survival.

Life in the Slow Lane: Ecology and Conservation of Long-Lived Marine Animals

1999 ◽  
Keyword(s):  
Life History ◽  
Population Growth ◽  
Growth Rates ◽  
Anthropogenic Impacts ◽  
Survival Rates ◽  
Conservation Strategies ◽  
Adult Survival ◽  
Population Growth Rates ◽  
Important Prey ◽  
The Status

<em>Abstract.</em> —Seabirds become mature at a late age, experience low annual fecundity, often refrain from breeding, and enjoy annual adult survival rates as high as 98%. This suite of life history characteristics limits the capacity for seabird populations to recover quickly from major perturbations, and presents important conservation challenges. Concern over anthropogenic impacts on seabird populations has led to the initiation of long-term field programs to monitor seabird reproductive performance and population dynamics. In addition, seabirds have been recognized as potentially useful and economical indicators of the state of the marine environment and, in particular, the status of commercially important prey stocks. This paper reviews demographic and life history attributes of seabird populations and uses this information to explore the consequences of longevity from the respective standpoints of conservation and monitoring goals. Analysis of a simplified life cycle model reveals that maximum potential population growth rates (λ) under ideal circumstances fall within the range of 1.03–1.12 for most species, though growth rates realized in nature will always be lower. Elasticity analysis confirms that seabird population growth rates are extremely sensitive to small variations in adult survival rates, and dictates that survival monitoring should be considered an essential component of conservation strategies. As in other organisms with long life spans, ecological and physiological costs of reproduction are expected to figure prominently in seabird reproductive decisions. Consequently, understanding how seabirds allocate reproductive effort in response to varying environmental conditions is an important prerequisite for correctly interpreting field data from monitoring studies.

Demography of the Porcupine caribou herd, 1983–1992

1994 ◽  
Vol 72 (5) ◽  
pp. 840-846 ◽  
Author(s):  
Steven G. Fancy ◽  
Kenneth R. Whitten ◽  
Donald E. Russell
Keyword(s):  
Survival Rate ◽  
Population Size ◽  
Computer Model ◽  
Rangifer Tarandus ◽  
Survival Rates ◽  
Annual Rate ◽  
Population Estimates ◽  
First Year ◽  
The Mean ◽  
Hunting Mortality

Population size, parturition rates, and sex- and age-specific survival rates were determined for the Porcupine caribou herd (Rangifer tarandus granti) in northeastern Alaska and northwestern Canada between 1983 and 1992. The herd increased at an annual rate of r = 0.0467 between censuses in July 1983 (n = 135 000), July 1987 (n = 165 000), and July 1989 (n = 178 000). The mean parturition rate for 225 radio-collared cows aged ≥3 years monitored for 603 reproductive attempts between 1982 and 1992 was 80% and did not differ among years. First-year survival of calves was 51%. The survival rate of calves through their first month differed among years (range 57–90%). The mean annual survival rate for ≥3-year-old caribou was 84.2% for 225 females and 82.6% for 42 males. Hunting mortality for the herd averaged 2–3% annually. Population estimates generated by a computer model using parturition and survival rates for the herd closely tracked population trends determined from photocensus data. Growth of the herd is most sensitive to the survival of females 3 years of age and older, followed by calf production and survival.

scholarly journals Demographic drivers of decline and recovery in an Afro-Palaearctic migratory bird population

2016 ◽  
Vol 283 (1842) ◽  
pp. 20161387 ◽  
Author(s):  
Catriona A. Morrison ◽  
Robert A. Robinson ◽  
Simon J. Butler ◽  
Jacquie A. Clark ◽  
Jennifer A. Gill
Keyword(s):  
Population Growth ◽  
Survival Rates ◽  
Bird Species ◽  
Migratory Bird ◽  
Adult Survival ◽  
High Survival ◽  
Population Declines ◽  
High Productivity ◽  
Population Growth Rates ◽  
Sub Saharan

Across Europe, rapid population declines are ongoing in many Afro-Palaearctic migratory bird species, but the development of appropriate conservation actions across such large migratory ranges is severely constrained by lack of understanding of the demographic drivers of these declines. By constructing regional integrated population models (IPMs) for one of the suite of migratory species that is declining in the southeast of Britain but increasing in the northwest, we show that, while annual population growth rates in both regions vary with adult survival, the divergent regional trajectories are primarily a consequence of differences in productivity. Between 1994 and 2012, annual survival and productivity rates ranged over similar levels in both regions, but high productivity rates were rarer in the declining southeast population and never coincided with high survival rates. By contrast, population growth in the northwest was fuelled by several years in which higher productivity coincided with high survival rates. Simulated population trajectories suggest that realistic improvements in productivity could have reversed the decline (i.e. recovery of the population index to more than or equal to 1) in the southeast. Consequently, actions to improve productivity on European breeding grounds are likely to be a more fruitful and achievable means of reversing migrant declines than actions to improve survival on breeding, passage or sub-Saharan wintering grounds.

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.

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