Constant Survival Rates Research Articles

Effects of Harvest on Annual Survival of Muskrats

Muskrats (Ondatra zibethicus) were marked from 1981 through 1984 and recovered for 5 years in Pool 9, Upper Mississippi River to determine survival and harvest rates by using banding methodology. Tag reporting rate, estimated from trapper interviews, averaged 83 ? 1% and was constant among years. Survival and recovery rates did not vary significantly between sexes but were significantly different between birth-year (BY) and after-birth-year (ABY) animals. Data best fit a model assuming constant age-specific survival and year-specific recovery rates. Constant annual survival rate of BY animals was 15.7 ? 2.3%, whereas survival of ABY animals was 5.8 ? 1.5%. Harvest rates ranged from 17% in 1982 to 45% in 1981, and averaged 32 ? 2% of the fall population in all years and habitats combined. Maximum sustained yield in backwaters was 20% of yield in openwaters although annual survival was not different between habitats. There was a density-dependent increase in nonharvest, birth-to-trapping season survival of juveniles, which compensated for increases in harvest mortality. J. WILDL. MANAGE. 51(2):265-272 The effects of exploitation on populations of vertebrates remains one of the important theoretical and applied questions in wildlife ecology. Originally, basic theory on the intercompensatory nature of mortality factors emerged from studies by Errington (1946, 1956, 1963) on the effects of natural predation in influencing abundance of prey species, particularly muskrats. His concepts on predation were extended to include effects of harvest on populations as a basis for management (Allen 1954, Hickey 1955). Wagner (1969:269) later concluded that the evidence that game populations can exist under heavy hunting pressure without obvious effects on their density was equivocal. Much recent research and discussion has focussed on migratory waterfowl (Anderson and Burnham 1976, Burnham and Anderson 1984, Nichols et al. 1984). Anderson and Burnham (1976:5-9) examined the effect of harvest on annual survival of mallards (Anas platyrhynchos) and defined the competing hypotheses of to a threshold point and totally additive, which form the basis for much of this paper. Despite the interest and importance of the effects of harvest on survival, details about mechanisms involved in the relationship between exploitation and population dynamics are poorly known. Therefore, in 1981, I began studies on muskrats on the Upper Mississippi River Fish and Wildlife Refuge (UMRFWR) to examine population responses to exploitation. Muskrats are an ideal study species because: large samples of muskrats are easily captured and marked, population densities vary substantially (Clay and Clark 1985), harvest effort varies in response to changes in trapping conditions (Clark 1986), and they provide a contrast to the studies on migratory waterfowl. Furthermore, practical management of muskrats rests on whether populations respond to changes in harvest in an inversity-compensatory manne (sensu Roseberry [1979]). Clay and Clark (1985) have previously shown density-dependent reproduction (inversity) in Pool 9 populations of muskrats. The task of demonstrating whether compensatory interactions exist between natural mortality and harvest remains. In this paper I examine the effects of harvest on survival, with the goal of contributing to both the theoretical basis for harvesting populations and the management of muskrats. A series of consequences of compensatory theory (Nichols et al. 1984) was examined in light of the Pool 9 studies. These results are an extension and, to some degree, a re-examination of previous results (Clay and Clark 1985) using more data and new techniques. The field work was funded through the Iowa Coop. Wildl. Res. Unit by the Upper Miss. River Basin Comm., U.S. Fish and Wildl. Serv., Iowa Conserv. Comm., and Wis. Dep. Nat. Resour. This is Paper J-12181 of the Iowa Agric. and Home Econ. Exp. Stn., Proj. 2401. R. T. Clay, K. L. Johnson, R. J. Munkel, K. R. Utterson, and R. E. Young conducted the marking and M. M. Anderson and J. Lyons facilitated tag recovery and contact with trappers. J. D. Nichols was particularly helpful with suggestions on parameter and variance estimation and interpretation. K. J. Koehler and H. D. Baker

Liberal use of emergency center thoracotomy

Emergency center thoracotomy is a heroic technique of resuscitation and treatment which was revived in the 1960s to improve the survival of patients presenting with cardiac wounds. With excellent survival rates attained in such patients, the technique was extended to victims of trauma with other mechanisms and locations of injury. At present, the technique has a survival rate ranging from 3 to 20 percent; however, most recent series of unselected patients show a survival rate of 8 to 10 percent. In this series, there were no survivors when emergency center thoracotomy was utilized after a period of prehospital cardiopulmonary resuscitation. Patients with isolated stab wounds to the thorax, especially those with cardiac injuries, had the best survival rate of any subgroup in the series. If emergency center thoracotomy was utilized for patients with some vital signs on admission and with neck or truncal gunshot wounds, blunt trauma, or abdominal trauma, the survival rate decreased to 2 to 4 percent; however, the small but constant survival rate in all of these groups justifies its continued use.

Constant-Parameter Capture-Recapture Models

Jolly (1982, Biometrics 38, 301-321) presented modifications of the Jolly-Seber model for capture-recapture data, which assume constant survival and/or capture rates. Where appropriate, because of the reduced number of parameters, these models lead to more efficient estimators than the Jolly-Seber model. The tests to compare models given by Jolly do not make complete use of the data, and we present here the appropriate modifications, and also indicate how to carry out goodness-of-fit tests which utilize individual capture history information. We also describe analogous models for the case where young and adult animals are tagged. The availability of computer programs to perform the analysis is noted, and examples are given using output from these programs.

Estimating Survivorship when the Subjects are Visited Periodically

Statistical methods for estimating and comparing constant survival rates are developed here for sampling designs in which survival of a subject is checked at irregular intervals. The maximum likelihood estimator is derived and shown to be readily calculated using an iterative procedure that starts with the Mayfield (1975) estimate as a trial value. Sampling distributions of this estimator and of the product of two or more estimates are skewed, and normalizing transformations are provided to facilitate valid confidence interval estimation. The sampling distribution of the difference between two independent estimates is found to be sufficiently normal without transformation to allow valid use of conventional normal theory procedures for testing differences and determining sample size for specified power. Statistical validity under the variable intensity sampling design does require that the duration of intervisit periods vary independently of observer perceptions concerning the survival status of the subject and, in order to achive robustness with respect to the assumption of constant survivorship, sampling intensity must vary independently of any temporal changes in the daily survival rate. Investigators are warned not to return earlier than planned to subjects thought to have died, as this observer behavior may cause serious bias in the survivorship estimate.

Observations on container-breeding mosquitoes in New Orleans, Louisiana, with an estimate of the population density of Aedes aegypti (L.).

In a survey of containers infested with Aedes aegypti (L.) conducted during September and October 1979 in a substandard residential area of New Orleans, LA, infestation indices were as follows: House--35, Breteau (foci)--85, Receptacle--69, Block--100, and Larval Density--169. A mean of 48.5 water-holding containers were found per block. More than 50% of these receptacles were narrow-mouthed containers, e.g., drink bottles, that held an average of less than 0.03 mosquito immatures each. After exclusion of data on the unproductive narrow-mouthed type, the average container held 7.8 liters of water, 105 1st and 2nd instars, 69 3rd an 4th instars, and 12 pupae. With assumed constant adult survival rates of 0.85-0.90 per day, the number of females per block on any particular day was estimated from pupal production data at 362-558, and the standing crop of females 12 days and older and therefore old enough to transmit dengue fever if they are vector competent was estimated at 51-158 per block.

An Analysis of the Generation-Mean Life Table of the Mosquito, Culex tritaeniorhynchus summorosus, with Particular Reference to Population Regulation

SUMMARY (1) A new type of life table, of which parameters are given as mean values for all generations existing during a mean generation time, is prop6sed for populations with incompletely overlapping generations. (2) This generation-mean life table is applied to the study of seasonal population changes of Culex tritaeniorhynchus summorosus Dyar in 14 ha paddy fields. (3) The estimation of developmental duration, which is essential to the construction of these life tables, is performed by temperature summation. (4) The relationship between the duration of each stage and air temperature is examined using published results and also from data obtained from larval rearing in cages set in paddy fields. (5) Employing these relationships, the mean generation times at different temperatures are calculated on the assumption that the ratio of lx (probability of surviving to the xth oviposition) to 11 and that of mx (mean number of female eggs laid by one female at the xth oviposition) to m1 are constant over the whole breeding season. The thermal constant and the developmental zero are 277.8 day-degrees and 10.1 ?C respectively. (6) The population growth rate per generation and the survival rate of larvae and pupae are estimated directly from their census data. (7) The proportion of females is regarded as constant (0.527). (8) Using these parameters, the expected fecundity (total number of eggs which one female is expected to lay during her complete life-time) is calculated on the assumption of a constant survival rate of eggs (0.951) and of equality between emigration and immigration. (9) Analysis of the life tables shows that the present population is regulated by density dependent processes. (10) There are two distinct equilibrium levels indicated by larval density. The first equilibrium level (133 m-2 in 1966 and 404 m-2 in 1967) is higher than the second (37 m-2 in 1967), and such a change is caused mainly by the increase of larval mortality due to the drainage of paddy fields, which however is not a key factor. (11) The most important regulatory mechanism may be intraspecific competition among larvae and it seems to be related closely to the spatial structure of the larval population.

Modelling Heron Survival Using Weather Data

There is a definite needfor methodology which will produce ageand time-specific survival probabilities from bird ringing studies in which only nestlings are ringed, and one possible approach to this problem is presented in this paper. Models are developed in which the survival rates for first-year birds are weather-dependent (and therefore time-speeific) and the rate for second-year birds is a constant, difterent from the constant annual survival rate assumed for all older birds, to describe the numbers of recoveries of rings from dead Grey Herons, A rdea cinerea, ringed as nestlings in Britain between 1955 and 1975. The models provide a good fit to the data and a useful and concise description of Heron survival. Comparison is made with the predictions of a modelfor heronry census data.

Animal Life Tables from Capture-Recapture Data

This paper provides equations that can be used to estimate the actual numbers of animals entering and leaving a population at different times, using capture-recapture data. On the basis of these estimates a life table could be constructed for a natural population, providing that emigration and immigration are negligible. The equations have been tested using simulation methods and have been found to require high sampling intensities for reasonably accurate estimates. The relevance of the work of Holgate [1964; 19661 to the estimation of constant survival rates has also been considered.

Estimating Survival Rates from Bird-Band Returns

Survival rates of birds can be estimated by releasing a group of banded birds at the beginning of each year for, say, s years and then recovering the bands from the dead birds for, say, t years. If the birds are banded as nestlings, then the younger birds tend to have a lower suaival rate than the adult birds and the methods used for estimation in this situation generally assume that the survival rate is age- dependent. However, adult birds tend to have a constant survival rate except when there are considerable fluctuations in the climatic conditions and similar factors from year to year. Thus, if only adult birds are banded, another approach to the problem of estimation is to assume that the survival rate depends on the calendar year and not on age the so-called time-dependent survival. A number of methods used in the past for estimating survival rates for both the age- and time-dependent models are discussed. It is shown both algebraically and by means of worked examples, that unless t is much greater than s, so that virtually all the birds are dead by the end of the experiment, all the methods discussed here tend to underestimate the true rates. The methods of Lack ( 1943 ) and Haldane ( 1953, 195S ), based on a constant survival rate are discussed and Haldane's method is generalized to the case when t 7& s. A regression method applica- ble to this situation is also discussed briefly. AGE-SPECIFIC SURVIVAL

A method for estimating natural survival rate and mean fecundity of an adult insect population by dissecting the female reproductive organs

SummarySeveral problems were discussed in relation toMacDonald's method (MacDonald, 1957) for estimating the survival rate of a natural population of adults with varying survival rates and unstable age structure. Random samplings with a fixed sampling ratio and an appropriate census interval is pre‐requisite during the occurrence of the adults. At each sampling, female adults are dissected to know the ratio, pi, of nulliparous females in ith sample (i=0, 1, 2, 3, …,). The Σnipi/Σni gives an estimate of the ratio, Fα/F, of nulliparous females in the population where ni refers to the population size on ith census date. If a constant daily survival rate is assumed, the daily survival rate is estimated from equation (4′). When the survival rate is not constant over the period of adult occurrence, e. g. before and after the initiation of oviposition, the survival rate during pre‐ovipositional period is estimated by equation (4″). Decision of an economic census interval to obtain a reliable estimate of the ratio, Fα/F, is depending on the form of emergence curve, particularly on its duration and the length of pre‐ovipositional period. If the normal distribution can be assumed for the emergence curve, an interval less than one third of the emergence period is recommended. Concerning with insects having a long pre‐ovipositional period, a census interval which exceeds one third of the emergence period still gives a good estimate of Fα/F. The mean realized fecundity of some kind of insects can be estimated by equation (5′ or 5″) using the estimates obtained by the present method.

Estimation of the stage‐specific survival rate in the insect population with overlapping stages

SummaryAn application ofHokyo andKiritani's method (1967) was attempted to estimate the stage specific survival rates of the population with overlapping stages. This method can be written as follows assuming a constant daily survival rate (K) throughout the life: urn:x-wiley:14383896:pope0143:equation:pope0143-math-0001 where, and F refer respectively to the total incidence of ith instar nymphs and that of individuals after ith instar inclusive, and αi refers to the developmental period of ith instar.Application of this model to caged and natural populations of the southern green stink bug, Nezara viridula, was made to test its validity. The estimates of the initial number of successive stages obtained from the present method were compared with those fromRichards andWaloff's method (1954) for the caged populations of 1st, 2nd and 3rd generations. The superiority of the present method to theRichards andWaloff's in estimating adult numbers was shown in all the generations examined. When different daily survival rates are involved in the course of population decrease, application of the revised method proposed byHokyo andKiritani (1967), gives much reliable estimate as compared with one before correction.The present method is useful in constructing life table of such species as scale insects which complete their life cycle within a defined space, but their successive stages overlap considerably.