Spring Density Research Articles

Behavioral Limitation of Round-Tailed Ground Squirrel Density

The two principal hypotheses of behavioral population regulation-territorial limitation and social stress-were tested in a 4-yr study of a high density, free-living population of round-tailed ground squirrels, Spermophilus tereticaudus, in Arizona. After copulation in early March, 22 to 3 1% of the adult squirrels, predominantly d 5, seemed to disperse. In late June, 29 to 45% of the juveniles, predominantly d d again, seemed to disperse. During the 2 yr of intensive study, these dispersal episodes were the major losses from the population, and they were correlated with the onsets of territorial behavior among adults in March and among juveniles in June. This correlation supports the hypothesis that territorial behavior limits population density. However, intensive observation and 2 field experiments involving removal and introduction of juveniles and provision of supplemental food indicate that dispersal was not statistically related to local density, food availability, or aggression. Territorial aggression did not cause emigration of adults or native-born juveniles, though it probably prevented immigration of foreign-born juveniles, during the summer months. Dispersal was not suffi- cient to limit population density increase. There appeared to be an innate sex difference in juvenile dispersal tendency, perhaps including a differential response to food availability and litter size. In 1 yr, spring density was unusually high, and many squirrels were wounded in February and March. The population subsequently showed classical symptoms of physiological stress, including reduced repro- duction and poor survival. This episode supports the hypothesis that high density leads to socially induced physiological stress, which eventually reduces density. However, the stress did not prevent the squirrel density from reaching a much higher level in the following spring. There were relatively few wounds and no signs of stress at the higher density. Physiological stress was not predictably related to denstiy and was not sufficient to limit density increase. In summary, behavioral factors were not sufficient to limit squirrel density when food was abundant and predation rate was low.

Nematode numbers, biomass and respiratory metabolism in a beech woodland-Wytham Woods, Oxford.

The mean annual population density of nematodes in the litter and upper 6 cm of soil was found to be 368,000 m-2. Mean individual live weight biomass approximated 0.2 μg and mean biomass was calculated to be 74.6 mg live weight m-2. No evidence of seasonal vertical migration between the litter, 0-3 cm and 3-6 cm strata was found and on average these strata contained 21.9, 46.2 and 31.9% respectively of the total number of nematodes recovered. The equivalent biomass values were 26.14, 56.57, and 17.29%. Total numbers revealed a general picture of low densities in spring and high ones in early winter, whereas biomass m-2 was low in late summer - autumn and high in winter. The annual oxygen consumption of the extracted nematodes was calculated to approximate 0.211 m-2 (≈4.0 kJ m-2) but when corrected for the effect of individual biomass (weight specific oxygen uptake) was equivalent to an energy expenditure ≈6.0 kJ m-2 which in its turn, because of the efficiencies of extraction, probably accounts for only 87% of the total energy expenditure by the nematode fauna. The nematodes were estimated to be responsible for a minimum of 0.11% to a maximum of 0.13% of the total "soil" respiration. A production/biomass ratio of 5.16 was estimated as was a net population production efficiency of 36.63%.

Demography and Behavioral Ecology of California Quail on Vancouver Island

A fundamental problem in ecology is to find the reasons for the relative stability of animal numbers. Given that the intrinsic rate of increase (rm) is positive in all species, why over long periods of time is the net rate of increase (r) usually zero? One important stabilizing mechanism in some populations of birds is the phenomenon of inversity (Errington 1945); that is, the rate of summer gain is inversely proportional to the spring density of adults. Inversity appears to be a function of survival of the young between years rather than due to annual changes in fecundity (Hickey 1955). We studied the demography and behavior of California Quail (Lophortyx californicus Shaw) on southern Vancouver Island from 1969 to 1972. The purposes of the study were (1) to describe the demographic parameters of the population; (2) to determine if inversity occurred; and (3) to determine, if possible, the underlying mechanisms that could cause changes in survivorship between years. The specific null hypothesis that we tried to refute was that there was no intrinsic difference in the behavior of adults between

Analysis of mixed flocks of tits in the Botanical Garden of Tohoku University, Sendai

1. Based on data of 56 censuses in July 1961-January 1962 and 124 censuses in April 1962-April 1963, and of other observations during 1960-'65, the annual number fluctuations of Long-tailed Tit Aegithalos caudatus in the Botanical Garden of Tohoku University, Sendai, are analysed.2. As compared with territorial annual life cycle of Great Tit, the annual cycle of Long-tailed Tit is based on flock life with separate pair life in the breeding season, which is started in late December 11/2 month earlier than in the Great Tit.3. The number of breeding Long-tailed Tit was same as the number in previous winter flock. One male bird banded among 16 birds in 1962, nested near its birth place in 1963 and '64. It was found in the same summer and autumn-winter flocks of 1962, '63 and '64.4. Each bird in autumn-winter flock of Long-tailed Tit remains in the next spring in its winter flock (or feeding) range, the number of breeding birds in spring being about the same as that of winter flock. Thus, the home range and size of winter flocks are important in determining the breeding area and density in the next spring.

The Effects of Northward Dispersal on Growth Rate of Young, Size of Young at Birth, and Litter Size in Sigmodon hispidus

Northward dispersal in Sigmodon hispidus has not significantly affected early growth rate of young or size of young at birth. But there has been a significant increase in litter size in the northern population. Northern S. hispidus have the same size young, but more young per litter than the southern population. Maintenance of the size of young at birth in northern populations may be related, in part, to the development of thermoregulatory capabilities. In the northern population there was seasonal variation in litter size, growth rate (tail length), and size of young at birth (tail length and body weight). Litters of S. hispidus produced in cold weather months are significantly smaller than those produced in warm weather months. INTRODUCTION The northward dispersal of the hispid cotton rat (Sigmodon hispidus spp.) has been well documented over most of its geographical range (Patton, 1941; Rinker, 1942; Cockrum, 1948; Anderson and Berg, 1959; Jones, 1960, 1964; Mohlhenrich, 1961; Genoways and Schlitter, 1966). With increasing latitude, populations of S. hispidus encounter increased seasonal climatic variability and longer cold periods. Populations of S. hispidus show both seasonal and irregular long-term fluctuations in density. Irregular fluctuations in population, frequently to plague proportions, have been reported in both southern and northern populations (for a review of the literature see Goertz, 1964). Odum (1955) demonstrated three well-marked long-term cycles in a southern population of S. hispidus hispidus, although in all years the autumn density of cotton rats was markedly greater than the spring density. He considered the latter type of variation a northern-type seasonal cycle in these populations. Northern-type in density have also been observed in other southern populations of S. hispidus (Erickson, 1949; Dunaway and Kaye, 1964). In northern populations of S. hispidus, seasonal in population are better defined and more regular as a result of decreased temperature (and increased duration of low temperatures) associated with increased latitude (Goertz, 1964; unpublished data). Variation in S. hispidus populations appears to be regulated by temperature (Baumgartner, 1945; Sealander and Walker, 1955; Dunaway and Kaye, 1964; Goertz, 1964). Goertz (1964) found that a long period of below-freezing weather, snow cover, and frozen ground coincided with a population decline. Similar declines had four factors in common: (1) high summer and autumn population density; (2)

Krenologia obszarów młodoglacjalnych na przykładzie Pojezierza Lubuskiego – przegląd badań

The Polish Lowland is an area with rare and relatively poorly studied springs. The present paper review results of recent studies on springs, their hydrology and environments on Lubuskie Lakeland (5.200 km2) in western part of the Polish Lowland. This area contains over 1,000 springs and seepages outflowing from porous sediments. Most of them are related to thick Pleistocene sediments containing several groundwater bearing layers, which are cut by deep subglacial channels (tunnel valleys). The spring density index is the highest in catchment of the Gryżynka River, with up to 4.8 individual springs and seepages per 1 km2. The most common in the Lubuskie Lakeland are seepages (65%), descending and hillslope outflows. Their water discharge varies from < 0.001 to 50 000 dm3/s. Hydrochemistry of spring waters is dominated by calcium and bicarbonate ions, as well as high concentrations of iron and manganese. Due to the lack of a surface insulation layer, contaminants (various forms of nitrogen) easily migrate to groundwater. Generally, the spring waters have good quality. Moreover continuous observations of the water surface levels in spring supplied water bodies revealed daily fluctuations, which are likely due to evapotranspiration and changes of the filtration coefficient in hyporheic zone.

The ecology of shallow water meiofauna in two New England estuaries.

The distribution and abundance of shallow subtidal meiofauna in four habitats in the Niantic and Pettaquamscutt estuaries in southeastern New England were studied from October 1964 through October 1965. Numbers of individuals ranged from 1,184 to 5,163/10 cm2, and wet weights from 8.5 to 62.5 mg/10 cm2. Nematodes were the dominant group, averaging 83% of the total numbers and 64% of the total biomass. Among the nematodes, epigrowth-feeding species were dominant at all four stations; in addition, deposit-feeding species were abundant at three stations where the amount of detritus was high relative to the fourth station. At these three stations ostracods and deposit-feeding polychaetes were also abundant.Nematodes showed marked seasonal changes i their species composition, with epigrowth-feeding species reaching maximum densities in spring and summer (coincident with observed increases in benthic microflora production), and deposit and omnivorous-feeding species in fall and winter (coincident with observed increases in organic detritus). Increases in the epigrowth feeders were responsible for significant increases in the total nematode populations in spring and summer.Ostracods were most abundant in late summer, fall and winter in association with the increases in detritus. Polychaetes, amphipods and lamellibranchs were most abundant in summer, the first-named in association with elevated water temperatures. Harpactacoid copepods were inconsistent in their seasonal distributions.Approximately 80% of the meiofauna occurred in the upper 3 cm of sediment. Copepods and ostracods were virtually limited to the upper 3 cm, while amphipods and lamellibranchs were limited to the upper 2 cm of sediment. Nematodes and polychaetes extended down to 5 cm (the lowest depth studied), although usually in significantly reduced numbers.

A Demographic Analysis of Fenced Populations of the Whiptail Lizard, Cnemidophorus tigris, in Southern Nevada

Between 1964 and 1967, spring densities of Cnemidophorus tigris in four study areas in southern Nevada ranged from 3-8 per acre. Estimated biomass ranged from around 43 to 114 g/acre. The sex ratio was 1:1. Minimal annual survival of adults was 54-60%, and life-spans of at least 7 years are postulated. An undetermined proportion of mature females laid two clutches of eggs in 1965, but the general pattern was one clutch of 2-4 eggs per year. Large females produced more eggs than small ones. Occasionally females 9-10 months of age laid eggs, but sexual maturity normally was attained at about 21 months. By assuming that all mature females laid two egg clutches in 1965 our fecundity estimates could be approximately reconciled with the observed size and age composition of populations in the spring of 1966. Possible compensatory errors in this analysis are discussed. One of the challenging problems of contemporary ecology is the analysis of ecosystems and the development of mathematical models capable of simulating the trophic transfers of energy and materials and the interactions between species which collectively constitute ecosystem function. This endeavor requires not only an understanding of the processes of primary production, but also the roles of primary and secondary consumers. The net production and material transfers of a consumer population can be estimated only if one understands the time changes in the structure and size of such populations, i.e., the rates of age-specific mortality and the schedule of recruitment by which the population is sustained. In another paper we have discussed the demography of Uta stansburiana and related annual changes in densities of this species to changes in schedules of female survival and fecundity (Turner et al., 1 Present address: PO Box 236, Zion National Park, Springdale, Utah 84767

Indices to Overwinter Survival and Productivity with Implications for Population Regulation in Pheasants

Two indirect indices for measuring relative overwinter survival and annual productivity (reproduction plus spring-fall survival) are described for Wisconsin pheasants (Phasianus colchicus). These are applicable to any species in which indices of both spring and fall density are available. Overwinter survival is indicated by the ratio of spring population index to the density index of the previous fall. Productivity is measured by the ratio of fall density measurement to that of the spring population in the same year. These ratios, when correlated with fall and spring densities, indicate the degree to which overwinter survival and productivity are related to population density. Applied to statewide Wisconsin pheasant data (with spring hen indices based on crowing-cock counts X winter sex ratios, and cock-kill estimates serving as fall density indices), this approach suggests that overwinter mortality is not appreciably density dependent and spring densities are a function of the preceding fall levels. Productivity is inversely correlated with breeding density, but the variations occur within limits and fall density is a function of the spring breeding population. This paper describes a method for deriving indices of overwinter survival and productivity in statewide Wisconsin pheasant populations with the use of spring and fall population indices. We also present insights which the analyses permit into regulatory mechanisms within this population. In most species of upland game, annual mortality and survival rates can be approximated from fall population indices and age ratios. However, in many cases we do not have reliable estimates of the seasonal pattern of mortality and annual variations therein. Where actual counts of fall and spring numbers are possible, overwinter loss can be estimated simply by comparing the two (for example, Errington 1945). But in most species, particularly over large geographic areas, we more commonly measure populations with such relative indices as kill estimates and roadside counts. The method here described derives relative indices of overwinter survival that are applicable to any species in which spring and fall population indices are available. Productivity measurements are generally available in upland game species through nesting, brood, or age-ratio studies. The prese t method describes a simple means for measuring productivity, again with the use o ly of semiannual population indices and without the need for specialized productivity surveys.

The Regulation of Density in a Natural Population of the Pond Snail, Lymnaea Elodes

The role and mechanisms of density regulation were studied in a natural population of the pond snail, Lymnaea elodes, in a small permanent pond in southern Michigan. A portion of the snail's habitat along the margin of the pond was subdivided into 28 artificial snail—proof enclosures (pens). In two groups of four pens each, adult densities were altered to about 1/5 and 5 time initial spring density estimates (roughly 1,000/pen). A third group of four pens was left unaltered as a control. Sampling in these pens verified that alterations in adult density were maintained. The percentage of dead adults did not vary significantly among the three treatments, indicating the absence of any regulation to the numbers of adults through differential survivorship. On three dates in July the pens were sampled. Each time an inverse relationship was found between the densities of adults and young. A later, more extensive set of samples was taken after the margin of the pond was dry and the snail population in estivation. These samples showed no significant difference in the number of young snails (roughly 5,000/pen) among the three groups of pens. While the population was reproducing, a time—limited search for eggs was made which showed no significant difference in the total number of eggs per pen among the three groups. Thus treatment effects (alterations in adult density) had entirely disappeared in the numbers of eggs and young snails. In other pens predators were added or excluded without their having any apparent effect on the numbers of young or adults. Additions of food in the form of frozen spinach to two pens at regular intervals resulted in a dramatic (25—fold) increase in adult fecundity and an increase (4— and 9—fold on two separate dates in July) in the numbers of young. The differences between fed and unfed pens were taken as strong evidence for the presence of food limitation in the snail population, but there were indications that the limitation was one of a relative and not an absolute nature. There was an abundance of vegetation and coarse debris, but a lack of high quality food necessary for maximum fecundity and growth. Concurrent with the pen experiments, the general dynamics of a portion of the snail population not under enclosure was followed. Generally 12 to 24 samples were taken weekly from transects outside the pens. When the field data on growth and reproduction are compared to similar data from animals raised in the laboratory with superabundant food, it is obvious that field animals are realizing only a portion of their potential for fecundity and growth. These differences are attributed to food limitation. Field estimates of young snail mortality ranged from about 93 to 98%, but there is no evidence that this mortality was regulatory. Within the framework of the 20—fold differences in adult density in the altered pens, there is no indication that juvenile mortality contributed to the final observed convergence in densities of young. There are indications from other sources that mortality may be a potential regulatory force. The regulation of density in the pond snail was far more complete and occurred more rapidly than was thought possible. Although the mechanisms of the regulation are not as clear as the demonstration of their existence, the data strongly suggest that it was mediated through food limitation as expressed in fecundity.