Adult Female Survival Rates Research Articles

Local survival in Semipalmated SandpipersCalidris pusillabreeding at La Pérouse Bay, Canada

A hierarchical modelling approach was used to examine adult and age‐specific survival in an 8‐year study of breeding Semipalmated SandpipersCalidris pusillaat La Pérouse Bay, Canada. The survival of adult sandpipers was best described by a model with time dependence in local survival rate and probability of recapture. Annual variation in the local survival rate of adults was not correlated with nest success, timing of breeding or “return rates” and was not biased by an effect of first capture. Local survival rate of adult females (0.56, 95% c.l. = 0.51‐0.61) was consistently lower than that of adult males (0.61, 95% c.l. = 0.56‐0.66); these estimates were comparable with data from other shorebirds. The survival of returning young was best fitted by a model with both age and time dependence in local survival rate and probability of recapture. We evaluated our estimates of local survival rate with reference to patterns of breeding fidelity and philopatry in Semipalmated Sandpipers and other shorebirds.

Comparative Toxicity of Fenpyroximate to the Predatory Mite, Amblyseius womersleyi SCHICHA and the Kanzawa Spider Mite, Tetranychus kanzawai KISHIDA (Acarina: Phytoseiidae, Tetranychidae)

The relative toxicity of fenpyroximate to the predatory mite, Amblyseius womersleyi SCHICHA and the kanzawa spider mite, Tetranychus kanzawai KISHIDA was evaluated in laboratory studies. Adult females and eggs of both species were placed on bean leaf discs dipped in several concentrations of fenpyroximate. Fenpyroximate was much less toxic to A. womersleyi than to T. kanzawai, Although the survival rate of adult females of A. womersleyi tended to decrease with increasing concentrations of fenpyroximate, 58-74% of the predators survived at concentrations of 6.25-50 ppm. However, reproduction was not significantly reduced at any of the concentrations tested. At 6.25-50 ppm, fenpyroximate did not affect the hatch ability of A. womersleyi eggs or the development time of immature predators. Survival of immature predators significantly decreased with increasing fenpyroximate concentration, however, 16-48% of immature predators reached adulthood at 6.25-50 ppm. Adult female predators survived on a diet of spider mites intoxicated with fenpyroximate, and their fecundity and the sex ratio of the progeny were not significantly affected. Fenpyroximate at selective sublethal concentrations (i, e., 6.25-12.5 ppm) could be of value in adjusting the prey/predator ratio in integrated management of T. kanzawai.

Survival rate and sex ratio in habu, Trimeresurus flavoviridis (Viperidae), on the subtropical Okinawa Island, Japan

We examined the age structure and sex ratio of a viperid snake, Trimeresurus flavoviridis, based on samples collected by hand by local inhabitants, habu hunters and by baited traps in the middle and south of Okinawa Island, Japan. Small individuals had a low possibility of capture in all the collecting methods. The age structure was estimated through summing up the age frequency in each snout-vent length (SVL) class in samples with a similar SVL structure. From the age structures, annual survival rates of adult females and males were estimated to be 0.7 and 0.8, respectively. In most samples the sex ratio was biased towards males, especially in March and August and in large individuals. However, the female proportion increased in June.

Density dependence in a fluctuating wild reindeer herd; maternal vs. offspring effects.

The Hardangervidda wild reindeer herd in Norway is the largest in Western Europe. It has fluctuated between 7000 and 32000 animals during the last 35 years. Four density-dependent effects were found: 1. A food limitation effect due to a shift in diet after overgrazing lichen on the winter range. This led to increased tooth wear and lowered body size and fat reserves. 2. A significant correlation between population density and juvenile winter survival rate. No effect on adult female survival rate was found. 3. A cohort effect. After population increase and overgrazing, recruitment was reduced by 30% and remained so after population reduction. Birth weights had increased by 30% 5 years after population reduction and the mean calving time was earlier. As a result, after population reduction weights of newborns were 40% greater at a comparable date. Neonatal survival rate was related to maternal condition during the last part of gestation which coincides with the peak winter snow accumulation. The slow increase in adult dressed body weights (DBW) after population reduction is due to the combined effects of increased tooth wear when winter range was limiting and to the cohort-generation time, so that an improvement in neonatal survival and size was first expressed in subsequent offspring cohorts. 4. An inter-generation effect. During 30 years of resource limitation, DBW decreased by 23%, birth rate was unchanged after the first peak, while fecundity increased by 15%, suggesting increased reproductive effort per unit body weight. Natural selection for increased reproductive effort by smaller females when food was limiting was suggested. Some size-effect due to hunters selecting the largest adult phenotypes was possible but not the main cause. These results do not support some earlier hypotheses about the effects of population density on size at maturity in ungulates.

Survival Rates Required to Sustain Bear Populations

A simple approximation to the Lotka equations permits using various combinations of population dynamics parameters to determine adult female survival rates needed to sustain a constant population level under various conditions suggested by observed data on grizzly (Ursus arctos) and polar bears (U. maritimus). The approximation should be useful in evaluating more complex models. Some data on polar bears were used to illustrate a method for estimating the ratio of early survival rates to that for adults. Such a ratio may be useful in establishing appropriate combinations of subadult and total adult survivorship for sustained population levels

Life History of Trichopria stomoxydis (Hymenoptera: Proctotrupoidea: Diapriidae) a Gregarious Endoparasite of Stomoxys calcitrans from Zimbabwe, Africa

A gregarious species of Trichopria stomoxydis Huggert, (Hymenoptera: Prototrupoidae: Diapriidae) collected near Harare, Zimbabwe, Africa, and host-specific for Stomoxys calcitrans (L.) was studied. It was endoparasitic, using the body of the host as a cocoon within the puparium. Males emerged first, and mating occurred as soon as the females emerged. Females preferred pupae <24 h old, but would parasitize 1-, 2- and 3-day-old pupae. Oviposition time was 30-45 min, with one oviposition wound per host. Immature development was 13-18 (X 15) days, with a male-to-female sex ratio of 1:3, and a growth rate of 7.9 fold. Each pupa was capable of producing 6-20 (X 11.5) females. The daily survival rate of adult females was 0.3419.

Sexual differences in survival rates of adult pipistrelle bats (Pipistrellus pipistrellus) in South Sweden.

A pipistrelle bat (Pipistrellus pipistrellus) population in southernmost Sweden was studied for eight consecutive breeding seasons by means of bat boxes. Survival rates were calculated using Cormack's stochastic technique. The mean survival rate of adult females exceeded that of territorial males. Annual variations in survival rates were most evident in males, low rates being observed in years following wet autumns. Energy constraints imposed on territorial males by the mating system, a resource defence polygyny, were assumed to account for the differences obtained in survival rates between the sexes.

Mathematical Demography of Spotted Owls in the Pacific Northwest

We examined the mathematical demography of northern spotted owls (Strix occidentalis caurina) using simple deterministic population models. Our goals were to gain insights into the life history strategy, to determine demographic attributes most affecting changes in population size, and to provide guidelines for effective management of spotted owl populations. The spotted owl apparently has evolved high adult survival rates associated with irregular and unpredictable reproduction. The finite rate of population change (X) in this subspecies is most sensitive to variation in adult survival rate and relatively insensitive to variation in fecundity and age at first reproduction. However, rates of population change are strongly affected by reproductive senescence if it occurs before 15 years of age. Sound management practices should include efforts to control factors that adversely affect the survival rate of adult females. J. WILDL. MANAGE. 54(1):18-27 Considerable interest has developed over the harvesting of old-growth forests in the Pacific Northwest and impacts on the long-term survival of the spotted owl. Current information suggests that the northern subspecies (S. o. caurina) is restricted to coniferous forests in mature and old-growth age classes (Forsman et al. 1984, see Gutierrez and Carey 1985) and that continued loss and fragmentation of the remaining old-growth forests may threaten the viability of the subspecies. The possible endangerment of the subspecies and the need to retain large areas of suitable habitat have generated heated debate because of perceived economic costs to the timber industry associated with setting aside large areas of older forests for the spotted owl (Dixon and Juelson 1987, Salwasser 1987, Simberloff 1987). In a search for solutions to this dilemma, the Forest Service (U.S. For. Serv. [USFS] 1986) and the academic community (Dawson et al. 1986) identified various aspects of the owl's biology and life history for further investigation and proposed guidelines for spotted owl research. An aspect of the owl's biology that was addressed in detail by both groups was the species' demographic life history. The apparent decline of the northern subspecies may be exacerbated by low preadult survivorship, low adult fecundity, and delayed age at first reproduction. These were features identified as primary parameters that should be estimated more precisely. Neither report gave a high priority to the annual adult survival rate even though adult survival rate significantly affects the rate of population change of both the California condor (Gymnogyps californianus) (Mertz 1971, Verner 1978) and the snail kite (formerly the Everglade kite [Rostrhamus sociabilis]) (Nichols et al. 1980), species with demographic characteristics similar to those of the spotted owl. The conclusions by Dawson et al. (1986) and the USFS (1986) concerning the relative importance of various demographic parameters of the spotted owl have recently been criticized by Lande (1988). Our goal was to characterize the life history structure of the spotted owl and to determine demographic parameters that most influence rates of population change. Detailed, analytical analyses of a species' life history structure are not only a necessary prerequisite to understanding its population dynamics, but also suggest direction for future research. We analyzed the available demographic data of the northern spotted owl using life history and demography in an approach similar to Mertz (1971) and Nichols et al. (1980). We also assessed the direction of current spotted owl research and suggest future priorities indicated by our demographic analyses. The owl's basic demographic life history includes several parameters; however, accurate and precise estimates of all parameters are not available and these parameters might exhibit substantial geographic variation throughout the range of the northern spotted owl. It is thus of considerable interest to examine the effects of parameter variation on projected population

A Fur Seal Population Model Based on Age Structure Data

About 16 000 female fur seals from the Pribilof Islands population were aged in pelagic collections from 1958 through 1974. A simple simulation model of the female population was used to vary population parameters until a minimum chi-square value was achieved for the fit of simulated annual age structures to those observed in the pelagic collection. Population trajectories resulting from either a diminishing reproductive rate or diminishing adult female survival rate approximated estimated pup population sizes, which were not used in developing the model, except that a subset of five observations was used to constrain model trajectories to the general neighborhood of the observed pup populations. The main finding of the study was that adult female survival rates varied sharply during the 1964 through 1974 period, after the major period of harvests of female fur seals. Further study of the age structure data may thus be useful in evaluating the poorly understood long-term reduction in abundance of Pribilof fur seals.

The spring decline in the meadow vole, Microtus pennsylvanicus: the effect of density

The densities of six Microtus pennsylvanicus populations were reduced by removing large, sexually mature adults 6 months prior to (fall removal manipulation) and just prior to (spring removal manipulation) anticipated spring declines. When the spring decline on the control grid was a result of short distance dispersal, the manipulations had no effect; when it was a result of in situ mortality and (or) long distance dispersal, the fall removal manipulation produced a significant improvement in the survival rates of adult males. Adult female survival rates were high and unaffected by the manipulations. Adult reproductive rates were high and similar on all grids. The onset of the females' breeding season was advanced by the manipulations in two trials. Home range sizes were similar for all animals during the nonbreeding period. During the breeding period, males and females on the experimental grids had larger home ranges than those on the control grids.