Population dynamics and morphometries of Gammarus pulex L.: evidence of seasonal food limitation in a freshwater detritivore

SUMMARY. 1. Seasonal changes in population size structure of Gammarus pulex L. in a Cotswold stream appeared to indicate a growth check in late summer.
2. The relationships between dry weight and body length, and between the number of primary flagellar segments on the first antenna and either dry weight or body length provided further evidence of a reduction in growth in mid and late summer.
3. Body fat content was minimal (4% of dry weight) at the end of summer, when large particulate organic detritus was scarce or of poor quality, and maximal in late winter (17.9% dry weight in females; 9.4% in males), after a period of high food availability. In a field experiment, the fat content of animals in summer was raised to levels typical of winter by providing high quality food.
4. Field and experimental evidence together strongly infer that this population of G. pulex was subject to severe food limitation from early summer until leaf fall in autumn.     

Seasonal changes in density, demography and body composition of small mammals in a southern temperate forest

Eleven small mammal species (nine rodents and two shrews) were recorded in 16 months of trapping in the Karkloof Forest, Natal. Total densities varied seasonally, ranging from 60.7 animals/ha in the dry autumn and winter to 29.1 animals/ha at the onset of the rains in spring and early summer. Peaks in breeding coincided with high body fat and water content in the five common species during summer: in winter, when body fat and water levels were low, there was no breeding. This may be related to poor food quality at this time. Annual changes in density, breeding season and juvenile recruitment of Rhabdomys pumilio, Mastomys natalensis and Myosorex varius are the same as recorded in conspecific populations from other habitat types and do not seem modified by the habitat stability of the forest environment. Of the five common species, only Grammomys dolichurus , one of the few forest-associated small mammals in southern Africa, and Graphiurus murinus demonstrated stable, K-selectéd life-history styles.     

Annual variation in energy reserves in male three-spined stickleback, Gasterosteus aculeatm L. (Pisces, Gasterosteidae)

Wet and dry weights of tissue were measured and concentrations of glycogen, lipid and protein were estimated for the liver, gonad and carcass of male sticklebacks from an annual population collected each month over one complete year. In young-of-the-year there is one period of rapid weight gain, in all three body regions (liver, carcass and gonads) but particularly of the carcass, in the autumn and a second in spring and early summer. This is accompanied by an increase in the water content of all three body regions. The gonadosomatic index also increases sharply in spring and early summer. Young sticklebacks accumulate lipid and glycogen slowly during the autumn and winter of their first year of life and more rapidly from late winter to early summer. Thus, the period of most rapid accumulation of these reserves coincides with the time when body weight and gonad maturation are also increasing sharply. Lipid and glycogen levels fall during the reproductive season in those males that breed, so that by July they are reduced to 43% and 37% (respectively) of their peak values in May. Levels of protein increase throughout the year as the fish grow, but in breeding males by July the concentration of protein in the carcass falls to 70% of pre-breeding levels. Breeding males therefore reach the end of the reproductive season with their total energy reserves severely reduced, and consequently they suffer a very high mortality. In contrast, adult males that fail to reproduce survive beyond the breeding season. They continue to gain weight and to accumulate lipid and glycogen from August to September, but these energy reserves fall (to levels comparable to those of post-breeding fish) in December, when these fish probably die. These results demonstrate that in male sticklebacks, growth and gonad maturation can be sustained in parallel with the accumulation of energy reserves, which are subsequently extensively depleted as a result of reproductive activities.     

Dynamics of Chlorophyll <Emphasis Type="Italic">a</Emphasis> Content in the Ob River and its Relationship with Abiotic Factors

Seasonal and interannual dynamics of phytoplankton content (chlorophyll a), organic matter, and nutrients, as well as water temperature and water transparency, have been analyzed for the weekly observations performed in the Ob River from February to November, 2012–2015. The period of intensive phytoplankton growth (>10 mg/m³ Chl. a) lasts 70–90 days at a long spring flood in average and high-water years; in the absence of flooding during a dry year it exceeds 110 days. Seasonal phytoplankton dynamics is characterized by two summer maxima in July–August and in September (Chl. a content ~25 mg/m³); during a dry year, there is also a peak in June (up to 37.3 mg/m³). Seasonal dynamics of Chl. a in summer–autumn low water is closely related to the water temperature; in high water and autumn low water it is closely related to water transparency; in summer it is closely related to BOD5; and, in the summer–autumn period, it is closely related with nitrate content. According to the annual average (5.7–11.1 mg/m³) and maximum (19.2–35.0 mg/m³) concentrations of chlorophyll a, the trophic status of the river corresponds to mesotrophic–eutrophic water and the water quality corresponds to the second class, i.e., “clean water.”     

Seasonal distribution of juvenile Atlantic cod in the southern Gulf of St Lawrence

Seasonal changes in the geographic distribution of juvenile (ages 1–4) Atlantic cod Gadus morhua were determined from research surveys conducted in the southern Gulf of St Lawrence during 1986–87, 1990–91, and 1994. From late June to early October, juvenile cod were most abundant in shallow water (<50 m deep). By early November, all age groups (adults and juveniles) had migrated to deep (>100 m) offshore waters for the winter. For most juveniles, this represented a minimum migration of >225 km (each way). Age 3 and 4 cod migrated greater distances than age 1 and 2 fish. Some age 3 and 4 cod migrated as far as 650 km from their summer and early autumn areas. Although there was partial geographic segregation of juvenile and adult fish during summer and winter, all age groups were found together during the migration. No cod were present in the shallow waters (<80 m deep) of the south-western Gulf during April due, in part, to later than average ice-melt. Large numbers of all age-classes were present in most of the south-eastern Gulf by mid-May.     

Seasonal hyperphagia does not reduce digestive efficiency in an Arctic grazer

Muskoxen (Ovibos moschatus) consume fibrous plants that grow rapidly over the short Arctic summer. We studied responses of eight castrated male muskoxen to a diet of grass hay and mineral supplements during spring, autumn, and winter. Animals gained body mass in spring (239+/-39 kg) as body fat content increased from 26% to 38% of ingesta-free mass in winter without changes in lean mass and protein. Intakes of dry matter (DM) increased by 74% between spring and autumn as digestible energy increased from 554 to 923 kJ kg(-0.75) d(-1) during mass gain. Digestibility of cellulose (72%-76%) was not affected by increasing food intake between spring and autumn but was reduced to 65% in winter. Digestibility of nitrogen compounds was 61%-66%, even though intake increased by 134% between spring and autumn. Excess dietary nitrogen from hay and supplements increased urea concentrations in plasma and urine. High loads of solutes such as potassium did not affect plasma or urinary osmolality but were associated with increased rates of glomerular filtration and urinary excretion. Low intakes of sodium from grasses may limit intake and digestion during summer, but high food intakes can support deposition of nitrogen, calcium, magnesium, copper, and zinc in body tissue even when dietary concentrations are low. Seasonal increases in digestive and metabolic functions allow muskoxen to rapidly accumulate energy and nutrients in body tissue during the short season of plant growth.     

Determinants of the dramatic seasonal changes in the intake of energy and protein by Japanese monkeys in a cool temperate forest

Daily intake of gross energy (DGEI) and protein (DGPI) of Japanese monkeys in a cool temperature forest were investigated in different four seasons. As a result, dramatic seasonal differences in DGEI and DGPI were found: DGEI and DGPI in winter were significantly lower than those in spring and autumn, being only about 17–42% of those in the two seasons. DGEI and DGPI in summer were also lower than those in autumn and spring, being only about 29–52% of those in the two latter seasons. Seasonal comparisons of some variables on food qualities revealed that much lower values of DGEI and DGPI in winter and summer were influenced srongly not so much by the lower calorie and protein content of food as by the lower speed of dry weight intake. Multiple regression analyses for each food item revealed that the unit weight was a more important factor in determining the speed of dry weight intake than was the speed of unit intake. In addition, the speed of dry weight intake contributed much more to the speed of calorie and protein intake than did the content of calorie and protein. Multiple regression analyses, employing DGEI and DGPI (as dependent variables) and daily mean values of some variables related to food quality (as independent variables), revealed that the mean values of speed of calorie and protein intake on food items eaten in a day could explain 79.0% and 85.9% of the variance in DGEI and DGPI, respectively. In addition, the mean value of the speed of dry weight intake of food items eaten in a day can be used to explain 74.3% and 52.8% of the variance in DGEI and DGPI, respectively. These findings suggested that not only nutritional content of food but also the speed of dry weight intake strongly determined the nutritional condition of nonhuman primates. Am. J. Primatol. 41:267–288, 1997. © 1997 Wiley-Liss, Inc.     

SEXUAL AND SEASONAL, VARIATION IN CONDITION AND SURVIVAL OF SWEDISH GOSHAWKS ACCIPITER GENTILIS

Winglength was the most powerful intersex discriminator, giving 99.5% separation by itself and 100% combined with bodyweight or keel length. Females but not males, had longer wings and were heavier as adults than as juveniles. Pectoral fat and muscle indices explained 81–91% of variation in total fat and 93–96% of variation in total lean dry weight for male and female hawks but bodyweight change explained only 56–60% of variation in the fat index compared with 75–76% for pectoral lean dry weight. The best size index, keel length, explained only 6.4% of bodyweight variation in males and 11.2% in females. Winglength was very weakly correlated with keel length. Taking size difference into account, females were heavier with higher wingloading than males but had relatively lighter flight muscles and therefore a lower power availability relative to their flight requirements than in males. On the other hand, females had greater maximum fat stores (17% of bodyweight) than males (14%) and could have survived longer than males without food. These differences would be adaptive for the different role of each sex during breeding. The weight of first capture of live-trapped adults and juveniles increased between September and December, possibly because moulting (in adults) or hunting inexperience (in juveniles) kept weights low in autumn but also perhaps because the benefit of having large reserves for surviving, relative to the cost of decreased agility in flight because of increased wingloading, was greatest in mid-winter. Shot hawks weighed more than the live-trapped birds but showed the same trends, as did retrapped individuals. Females but not males, tended to lose weight in January before a further increase in the spring. Records of hawks retaken more than two months after first capture showed that between October and January survival in females but not males, was enhanced by high bodyweight. Since female weights were also significantly lower in southern Sweden than in central and northern areas, it is suggested that changing agriculture or other factors in the south may have reduced prey for females more than for males.     

Annual patterns in reproduction and perirenal fat of hares (Lepus europaeus) in sub-alpine Canterbury, New Zealand

The aim of this paper was to describe how the age, sex and reproductive state of hares affected the amount of fat found around their left kidney. A total of 2208 hares ( Lepus europaeus ) was shot and autopsied over 13 years from sub-alpine grasslands in Canterbury, South Island, New Zealand. Adult females may be pregnant from July to mid-March. Adult males' testis weights were highest from July to January, and some fertile males may have been present in all months but April. The amount of perirenal fat in adults increased in autumn, peaked in early winter, and decreased thereafter to low levels through spring and summer. Autumn fat deposition in males was not clearly related to reproductive state in individuals, although it coincided with seasonal testicular development. Autumn fat deposition in females may have been caused in part by the cessation of lactation, but, like that in males, the increase was also part of an endogenous pattern. Fat utilization in winter was related to breeding. In males, utilization coincided with reproductive activity and the amount of perirenal fat remained consistently low throughout the breeding season. In females, net fat utilization was associated with lactation but this was balanced to some extent by fat deposition induced by pregnancy. Females simultaneously lactating and pregnant were in finer balance between utilization and deposition. Other factors, such as the number of embryos and the stage of gestation, altered the fat balance in these hares. Fat was also deposited as a 'yolk-sac' in embryos.     

黑线仓鼠体重和能量代谢的季节性变化

为阐明小型哺乳动物体重和能量代谢的季节性变化以及生理调节机制,将黑线仓鼠驯化于自然环境下12个月,测定其体重、能量收支、身体组织器官和血清瘦素水平的季节性变化。黑线仓鼠能量摄入和支出的季节性变化显著,冬季摄入能、基础代谢率(BMR)、非颤抖性产热(NST)显著高于夏季。体重季节性变化不显著,但身体组织器官重量呈现显著的季节性变化,冬季肝脏、心脏、肾脏以及消化道重量显著高于夏季。体脂含量夏季最高,冬季最低,冬季显著低于夏、秋和春季(P <0.01)。血清瘦素水平的季节性变化显著,夏季瘦素水平比秋、冬季分别高88.2% 和52.4% (P <0.05)。结果表明,黑线仓鼠体重维持季节性稳定,与“调定点假说”的预测不同;但脂肪含量和血清瘦素季节性变化显著,符合该假说。夏季血清瘦素升高具有抑制能量摄入的作用,冬季血清瘦素可能是促进代谢产热的重要因子,瘦素对能量代谢和体重的调节作用与气候的季节性变化有关。       

内蒙古草原布氏田鼠和长爪沙鼠体重及身体成分的季节变化

研究了内蒙古草原布氏田鼠(Lasiopodomys brandtii)和长爪沙鼠(Meriones unguiculatus)的体重、身体脂肪、水分含量及身体热值等指标的季节变化.2种动物的体重都是在春季最高,布氏田鼠的体重具显著的季节变化,长爪沙鼠的鲜重具季节变化,但干重则基本维持恒定.2种动物的脂肪含量和身体热值都...     

Seasonal variations of physiological characteristics and thermal sensation under identical thermal conditions

Seasonal variations of human thermal characteristics were inspected in thermal comfort and when constantly indoors. Metabolic rate, tympanic temperature, skin temperature, body fat, body weight and thermal sensation were measured under identical thermal conditions in a chamber over the course of one year. Experiments were carried out for each subject in both summer and winter. Six subjects were measured 35 times in summer and 45 times in winter. one subject was measured weekly for 14 months. Measurements for analyses were taken 40-60 min after entrance into the chamber. Results revealed the following. 1) For all subjects, the metabolic rate, tympanic temperature and body fat were lower in summer than in winter; thigh skin temperatures were higher in summer than in winter. The averaged individual ratio of seasonal difference was 11.9% for metabolic rate, 14.9% for body fat, 1.8% for thigh temperature and 0.53% for tympanic temperature. Seasonal differences of about 10% in metabolic rate were maintained in this study. 2) Seasonal variations of the variables were examined for phase relationships against the outdoor temperature. 2-1) Metabolic rate, thermal sensation, body weight and body fat changed in reverse phase, whereas skin temperature was in-phase. 2-2) Skin temperature lagged by about one month in both summer and winter. Body fat also lagged by about one month in summer, but corresponded to the phase in winter. Metabolic rates were also in-phase in winter but led about three months in summer. Thermal sensations lagged by about three months in winter but were in-phase in summer. Body weight was in-phase in summer and winter. 2-3) Summer disorders were observed particularly in seasonal variations of metabolic rates, tympanic temperature, skin temperatures, and thermal sensation, thereby suggesting that the effect of temperature exposure was altered by air-conditioner use.     

Seasonal distribution and dive behaviour of harp seals (<Emphasis Type="Italic">Pagophilus groenlandicus</Emphasis>) of the White Sea–Barents Sea stock

Eight adult female harp seals (Pagophilus groenlandicus) of the White Sea–Barents Sea stock were tagged with satellite-linked dive recorders during the nursing period and followed from breeding in late February 1995 until moulting in late April 1995. Another ten adult harp seals of both sexes were tagged and followed from moult in early May 1996 until breeding in late February the following year. Between breeding and moult the seals were distributed along the coasts of Kola of Russia and eastern Finnmark of Norway, coinciding in time and space with the spawning capelin (Mallotus villosus). Between moulting and breeding they encircled the entire Barents Sea, mostly in open water, using the water column from 20 to 300 m, and in so doing by and large reflecting the annual migrations of the capelin. Capelin is therefore assumed to be the main source of prey for the White Sea–Barents Sea stock of harp seals, to be substituted, in part, by amphipods (e.g. Themisto libellula) in mid-summer and polar cod (Boreogadus saida) and herring (Clupea pallasii) in late autumn and winter. These data provide a baseline for the evaluation of the effects of future climatic change in the rich Barents Sea ecosystem.     

Seasonal variations in infestations of parasites in a Wood mouse Apodemus sylvaticus population in the West of Ireland

Seasonal variation in most of the metazoan parasites of a Wood mouse population was investigated by a statistical analysis of their frequencies in 11 samples of about 30 mice trapped regularly over one year. Numbers of the flea Ctenophthalmus nobilis , most mesostigmatid mites and the beetle Leptinus testaceus were correlated with breeding in the mouse population and may have been directly linked with it as all ofthese arthropods are common in Wood mouse nests. The tick Ixodes ricinus was abundant over the summer but scarce in winter. Its preponderance on male hosts is doubtless because they cover more ground than females. Flukes were commonest in summer, probably as a result ofthe period of intensive feeding on invertebrates by the mice which usually occurs in early summer. Female mice were more heavily infected, perhaps because of their increased food requirements in the breeding season. Abundance of flukes declined with the turnover in the mouse population in autumn. The infestation pattern of the nematode Capillaria muris sylvatici is similar and the possibility of an invertebrate vector is discussed. While older mice were generally more heavily infected with helminths than were young, this was least marked in the tapeworm Cataenotaenia lobata (which most likely has a mite as an intermediate host and may be picked up as soon as juveniles start grooming) and the roundworm Syphacia stroma (eggs of which are almost certainly transferred by body contact between hosts)     

云南南亚热带北缘地区稻田亩产吨粮的种植模式及其生态生理学研究

1996～ 1 999年 ,在云南省蒙自县草坝镇 (南亚热带北缘 )进行了亩产吨粮的种植模式研究。通过对春、夏、秋、冬播玉米 ,早、中、晚稻以及冬小麦的系统研究 ,以地上部分总干物重、籽粒产量、总入射辐照量、叶面积持续期 (灌浆期 )、氮肥的利用率和生产力、水生产力为指标 ,对早稻—晚稻、早稻—秋玉米、早稻—冬小麦、春玉米—晚稻、夏玉米—冬小麦、中稻—冬小麦和中稻—冬玉米 7种复种模式作了比较 ,选出中稻—冬玉米为一年两熟亩产吨粮的最佳种植模式。     

Seasonal changes in production and nutrient content ofCynodon dactylon (L.) Pers. subjected to water deficits

Seasonal changes in water relations, production and mineral composition were studied in a sward ofCynodon dactylon (L). Pers. subjected to water deficits during a dry summer, and at recovery in autumn. The experiment was carried out under Mediterranean field conditions. Water deficits during summer reduced total dry matter production by 60%, but in autumn there were no differences between treatments. Compared to well-watered sward, the sward grown under drought showed an increase in potassium, calcium and nitrogen of 55, 10 and 10% respectively. These differences decreased with the arrival of autumn rains. Leaf osmotic potential (Ψ_Π) fell during the dry summer to −2.8 MPa in well-watered plants and to −4.2 MPa in stressed plants. In autumn there were no differences between treatments. Nevertheless, relative water content (RWC) only decreased to 0.86 in droughted plants. In summer potassium contributed to the osmotic adjustment. In contrast, under water deficits a decrease of 71% in sodium and, to a lesser but significant extent decreases in phosphorus, magnesium and chlorine was observed. Nitrogen, phosphorus and sulphur showed low concentrations during summer and increased in autumn.     

Variations in body length, weight, fat content and survival inCoccinella septempunctata at different hibernation sites

Adults ofCoccinella septempunctata L. (Coleoptera; Coccinellidae) were sampled in four overwintering sites: one in England and three at different altitudes in the Czech Republic (350–1420 m above sea level) in autumn 1992 and spring 1993. Body length, dry weight and fat weight were measured. There were significant differences in body length between sampling sites in spring 1993, but not in autumn 1992. The average sex ratio (♀) in all samples was 1∶0.60 in 1992 and 1∶0.72 in 1993. Females were significantly larger and heavier, and contained more fat than males in both sampling periods. Dry weight and fat weight were positively correlated to body length at all sampling sites except at Ruzyne, in the Czech Republic. Adults hibernating at higher altitudes and away from their breeding and feeding habitats had significantly more fat than those hibernating at lower altitudes. Fat reserves were reduced by 30% during the hibernation at the top of the Krkonose mountain, in the Czech Republic, where temperatures were much lower, but more than half of the fat reserves were consumed during the overwintering period at the other sampling sites. The significance of body length and fat reserves in relation to adult hibernation sites and overwintering survival is discussed.     

Growth and survival strategy of the Antarctic mite Alaskozetes antarcticus

Growth and mortality rates of three juvenile instars and adults of the oribatid mite Alaskozetes antarcticus were measured over a twelve month period using field enclosures m Its maritime Antarctic habitat A pattern was found of rapid growth during the short summer period (0 2-0 4 μg dry weight increment per day) followed by gradual weight loss overwinter Most individuals completed one instar per year, reaching a premoult resting phase by late summer, with the moult being delayed and relatively synchronised early the next summer A small proportion of proto- and deutonymphs completed two moults within one summer period After the final moult adults overwintered again before commencing oviposition, suggesting that the life cycle (egg-egg) will take at least five years Mortality was not biased towards any instar or time of year Highest individual growth rates were obtained at a constant temperature of 7°C in the laboratory However expenmentai increase of mean field temperature from 2 7 to 4 3°C by use of a plastic cloche led to decreased growth, although no change in moulting frequency or mortality rate Laboratory survival was greatest at 2°C and decreased with increasing temperature
Alaskozetes antarcticus may be descnbed as 'a' (adversity) selected, showing an exceptionally long life cycle of five to six years and extensive physiological investment in survival adaptations Moult synchronisation in early summer, involving entering winter in the inactive premoult phase, will increase overwinter survival by reducing the chance of inoculative freezing from gut contents, and may be advantageous in maximising the time available for feeding during the subsequent summer, or ensuring proximity of the sexes after the final moult     

A RINGING STUDY OF THE MIGRATORY BROWN SHRIKE IN WEST MALAYSIA

Wintering Brown Shrikes frequent open lowland country, a habitat that is largely man-made in Malaya. Individuals are sedentary during the winter season, each occupying a restricted area and exhibiting territorial behaviour. The earliest observations each year in different parts of Southeast Asia indicate that the southward migratory journey is relatively rapid. In Malaya, migrants arrive from the first week of September to the third week of October. At a lowland netting station during 1964–68 a major part of the total catch was taken in the months of September and October. Only a small proportion of these early shrikes wintered in the netting area. No distant recoveries were reported, and the subsequent movements of birds that were not retrapped are unknown. Shrikes netted in September—October comprised 29% adults, 54% full grown (i.e. immatures plus poorly—characterized adults), and 17% juveniles. The mean wing-length was significantly longer among adults than among both other classes, which did not differ significantly. During the winter, all ages showed a progressive decline in wing-length until the flight feathers were renewed in a premigratory moult falling in February—early April. Moult recorded in four Brown Shrikes taken in October-November is interpreted as the completion of a post-nuptial moult, commenced on the breeding grounds before autumn migration. In April, after the premigratory moult, confirmed adults constituted 70% of the total trapped and apparent immatures 30%. The mean weight of September birds was lower than any other month except November. The low weight in November is partly correlated with the shorter mean wing-length of the sample; it may also reflect the seasonally unfavourable weather of this month. The mean weight in February was high, although all birds were moulting; the weather in this month is typically hot and dry. Highest weights were recorded in April, indicating the premigratory deposition of fat. Weights of birds trapped more than once at different intervals showed a small initial weight loss (2 g), followed by a recovery within four days and no long-term adverse effects. A comparison of September weights in Taiwan and Malaya provides a tentative basis for the calculation of fat reserves utilized on the migratory flight. The proportion of returns after one year was 11%, and after two years 1 % only. Most returning birds were present in the netting area during the latter part of the winter of initial ringing; it is suggested tentatively that imprinting of the wintering grounds may occur during this period. Ecologically in Malaya the Brown Shrike occupies a new habitat only gradually being filled by the resident Rufous-backed Shrike. There is no evidence of interaction between the two species.     

Population structure and dynamics of sympatric Apodemus species (Rodentia: Muridae)

This paper describes the population biology of sympatric populations of Apodemus sylvaticus and A. flavicollis in western England. Annual changes in population siie closely resembled those seen in allopatric populations such that simultaneous peaks in number occurred only in autumn and early winter. Numbers of A. sylvaticus were low and stable in early summer increasing rapidly in late summer and autumn and remaining high throughout winter before a sharp decline in spring. Numbers of A. flavicollis increased after the start of reproduction and continued to rise throughout summer and autumn. The period of major decline of this species was during early winter. Densities of A. sylvaticus and A. flavicollis were comparable with those cited in allopatric studies. Spring populations of both species consisted of cohorts first appearing in the late summer and autumn of the previous year. Few individuals present in spring survived the summer. Reproduction of A. flavicollis commenced four to six weeks before that of A. sylvaticus . Seasonal variation in mean weight of adult males and females also indicates that those changes, due to the acquisition of secondary sex characteristics and reproductive maturity, occur earlier in A. flavicollis than in A. sylvaticus . Data presented contain no evidence of interspecific competition and it is concluded that interspecific differences, chiefly asynchrony in reproduction and annual population cycles, contribute to their stable coexistence.