Early Juvenile Survival Research Articles

Population Dynamics of Deer Mice, <em>Peromyscus maniculatus</em>, and Yellow-pine Chipmunks, <em>Tamias amoenus</em>, in Old Field and Orchard Habitats

There are often several rodent species included in the small mammal communities in orchard agro-ecosystems. This study was designed to test the hypothesis that the population levels of Deer Mice (Peromyscus maniculatus) and Yellow-pine Chipmunks (Tamias amoenus) would be enhanced in old field compared with orchard habitats. Rodent populations were intensively livetrapped in replicate old field and orchard sites over a four-year period at Summerland, British Columbia, Canada. Deer Mouse populations were, on average, significantly higher (2.5 – 3.4 times) in the old field than orchard sites in summer and winter periods. Mean numbers/ha of Deer Mice ranged from 12.1 to 60.4 in old field sites and from 3.3 to 19.9 in orchard sites. Breeding seasons in orchards were significantly longer than those in old field sites, in terms of proportion of reproductive male Deer Mice. Recruitment of new animals and early juvenile survival of Deer Mice were similar in orchard and old field sites. Populations of Yellow-pine Chipmunks ranged in mean abundance/ha from 5.6 – 19.0 in old field sites and from 1.9 – 17.5 on one orchard site, with no difference in mean abundance in 2 of 4 years of the study. Recruitment and mean survival of Yellow-pine Chipmunks also followed this pattern. This study is the first detailed comparison of the population dynamics of these rodent species in old field and orchard habitats. These species should be able to maintain their population levels and help contribute to a diversity of small mammals in this agrarian landscape.

Influence of a granivorous diversionary food on population dynamics of montane voles ( Microtus montanus), deer mice ( Peromyscus maniculatus), and western harvest mice ( Reithrodontomys megalotis)

Feeding damage to forest and agricultural crops by voles of the genera Microtus and Clethrionomys occurs periodically in temperate and boreal ecosystems. Application of diversionary food is an alternative management practice that does not rely on a reduction in the target population. This study tested two hypotheses that a granivorous diversionary food, sunflower seeds, would (1) reduce feeding damage to tree seedlings by montane voles ( Microtus montanus) without enhancing abundance or other population attributes and (2) enhance population dynamics of non-target deer mice ( Peromyscus maniculatus) and western harvest mice ( Reithrodontomys megalotis) in old field habitats at Summerland, British Columbia, Canada in 1993–1995. Small mammal populations were intensively live-trapped on replicate control and food sites pre- and post-treatment in two (A and B) experiments (food application rates of 68.1 and 113.5 kg/ha). Mean abundance and recruitment of voles/ha were similar between control and treatment sites. Mean abundance and recruitment of deer mice was higher on treatment than control sites in Experiment B but not in A. Mean abundance and recruitment of western harvest mice was similar between control and treatment sites. Overall survival (28-day), early juvenile survival, and body mass showed no patterns for any of the species when comparing control and treatment sites. This granivorous diversionary food did not reduce feeding damage by voles to lodgepole pine ( Pinus contorta) seedlings. The supply of sunflower seed was likely insufficient to divert voles from feeding on trees through the overwinter (5–6 months) period. The predicted increase in numbers of deer mice and western harvest mice appeared only as brief pulses of animals, and hence may not have increased the intensity of competition with voles.

Effects of geographic origin on growth and food intake in Eurasian perch ( Perca fluviatilis L.) juveniles under intensive culture conditions

Survival, growth, and food intake of Eurasian perch ( Perca fluviatilis) juveniles from different stocks originating from various geographic regions of Europe were compared under the same conditions of laboratory-scale intensive culture. In Experiment 1, four stocks originating from Italy (I), southwest (SF) and northwest (NF) France, and Belgium (B) were examined at larval and early juvenile (initial body weight, IBW=0.53 g) stages. In Experiment 2, B stock was compared to a Finnish (F) one in two trials, including small (IBW=1.26 g) and large (IBW=32 g) juveniles. In Experiment 3, small (IBW=1.29 g) and large (IBW=7.33 g) juveniles from Polish (P), F, and B stocks were examined. In Experiment 1, body weight means at hatching and survival at the end of the larval stage were significantly lower in the I and SF stocks than in the B and NF stocks. In the early juvenile stage, survival and growth rates were significantly lower in the I and SF stocks than in the B and NF ones. In Experiment 2, {early juvenile stage} survival in the F stock was significantly lower than in the B stock, partly due to a higher incidence of cannibalism. During this stage, growth rates and food intake or feed efficiency in the F and B stocks were comparable, but at the end of the juvenile stage, the F stock outperformed the B one. In Experiment 3, survival in all the three stocks was comparable both in small and large juveniles. In contrast to the higher performance of F juveniles in Experiment 2, growth rates were comparable between the B and F stocks, and fish from the P stock had the highest growth rates. The results indicate a high level of variation within and between hatchery stocks in survival rates, growth rates, and food intake. These variations depended on the geographic origin of the fish, with the lowest survival and growth potentials being in the stocks originating from the southern regions. These findings highlight the interest in evaluating growth and food consumption of different Eurasian perch stocks. Such evaluation is a necessary tool for genetic selection in improving performance in perch aquaculture.

Improving initial survival in cultured seahorses, Hippocampus abdominalis Leeson, 1827 (Teleostei: Syngnathidae)

This investigation aimed at improving early juvenile survival in cultured seahorses, Hippocampus abdominalis. Phototaxis from birth until 2 months of age was tested and juveniles were found to be positively phototactic within this age range. A comparison of the effect of culture vessel background (white vs. black vs. clear jars) on feeding efficiency at 1 week and 1 month of age using Artemia as prey revealed an age-dependent effect upon both attack rate and capture success. At 1 week, both attack rate and capture success were higher for juveniles contained in clear jars, and capture success was higher in black jars, as compared with white jars. At 1 month, there was no significant difference in attack rate between different jars, although capture success was higher in clear and white jars than in black jars. In a top-illuminated glass aquarium, juveniles with access to the water surface had lower survival (mean±1 SE=50±4.5%) than those without access to the water surface (73.3±4.2%). This was due to the ingestion of air bubbles when preying on Artemia nauplii congregating near the water surface. For side-illumination there was no such difference. Glass aquaria that were side-illuminated and blacked-off upwards from the waterline supported high juvenile survival (80.4±4.0% per brood) from birth through to 2 months of age in four broods.

Fossil crocodilians as indicators of Late Cretaceous and Cenozoic climates: implications for using palaeontological data in reconstructing palaeoclimate

Abstract That the Earth's climate has cooled over the last 100 million years has been recognized since the early nineteenth century—the transition from the ‘hot-house’ world of the Cretaceous (a time interval without significant polar icesheets) to the ‘ice-house’ world in which we now live. Today, the dynamics (process) responsible for this change are being examined using computer models, especially General Circulation Models (GCM's). Through such work our understanding of the dynamics of the Earth system improves and our ability to predict future trends is enhanced. But, the success of modelling experiments can only be assessed by comparing results with observations (the pattern), which, for palaeoclimate, are drawn exclusively from the geological record. Palaeoclimate interpreted from geological data is invariably based on analogy with the Recent, the validity of which depends on corroboration from multiple lines of evidence. This requires the compilation and investigation of large, global datasets of well-constrained geological climate proxies. This study uses the palaeodistribution of fossil crocodilians to examine the spatial distribution of palaeoclimate during this transition. Fossil crocodilians have a relatively good fossil record and are climatically limited in the Recent. They also provide a manageable global dataset with which to investigate other issues that impinge on the use of geologic data for reconstructing palaeoclimate: taphonomy, sampling effects, time-averaging, tectonics, and, for fossils, palaeobiogeography and evolution. As such this study provides a possible template for examining other climate proxies in order to validate and hone palaeoclimatic interpretations. An analysis of modern crocodilians indicates that temperature is the principal influence on their global distribution, with the Coldest Month Mean temperature (CMM) of ≈ 5.5°C marking the minimum thermal limit for the group, corresponding today to a minimum Mean Annual Temperature (MAT) of ≈ 14.2°C. The duration of warmth during the year (partly indicated by the Mean Annual Range of Temperature, MART) is also important, as this affects early juvenile development and survival. The presence of standing water provides an essential thermal buffer against temperature extremes. By analogy, the palaeodistribution of fossil crocodilians suggests the following: during the Late Cretaceous and early Palaeogene MAT's in excess of 14.2°C (CMM's > 5.5°C) permeated throughout mid-latitudes and coastal regions in high latitudes; during the Oligocene the restriction of fossil crocodilians to low latitudes suggests high-latitude cooling, as indicated by numerous other lines of evidence—coeval restriction of crocodilians to coastal regions in mid-latitude North America and much of Asia, consistent with increased seasonality and aridification in continental interiors, may reflect local orographic changes as well as global climate change. During the Miocene fossil crocodilians return to the Great Plains of North America, but do not reoccupy the continental interior of Asia; by the Pliocene, crocodilians are again restricted to low-latitudes and coastal regions in mid-latitudes, coincident with further high-latitude cooling, and aridification and cooling of mid-latitude continental interiors. Minor distributional changes during the Holocene may reflect human effects.

The relationship between prey selectivity and growth and survival in a larval fish

We examined prey preference, growth, and survival of small larval (8-10 mm total length (TL)), large larval (11-17 mm TL), and early juvenile (>18 mm TL) walleye (Stizostedion vitreum) in laboratory aquaria and field mesocosms using multiple prey assemblages that included cladoceran, copepod, and rotifer prey of varied sizes. Both prey taxa and size affected prey preference during the larval period. All sizes of walleye avoided rotifer and nauplii prey. Small and large larvae selected for intermediate-sized (0.4-0.9 mm) cladoceran prey and selected against large prey (>0.9 mm) of both taxa. Although neither capture efficiency nor handling time differed between prey taxa, larvae oriented more frequently towards cladoceran prey suggesting that they were more visible than copepods to these small fish. Larval walleye that were fed exclusively cladoceran prey survived better than fish that were fed other prey. Early juveniles selected primarily on the basis of prey size, choosing large copepods and cladocerans. Prey taxa did not affect early juvenile growth or survival. Prey taxa and prey size interacted with predator size to influence selectivity and its effect on growth and survival. Consequently, these factors must be considered in combination when examining the importance of foraging decisions in young fish.

Effects of Incubation Temperature on the Hatching Success of Arctic Char Eggs

Abstract Samples of eggs from 18 families and from three groups of mixed families of Arctic char (Salvelinus alpinus) were incubated at 3°C or 6°C to determine if incubation temperatures affected hatching success and early juvenile survival. Mean (±SID) hatching success was 47 ± 30% in 6°C family samples and 65 ± 30% in 3°C samples. Hatching success was significantly greater at 3°C than at 6°C in 15 out of 18 families (paired t-test over families, P = 0.0014). After hatching, survival to 90 d at 9°C was 59 ± 22% for juveniles that had been incubated at 6°C and 76 ± 17% for juveniles incubated at 3°C. Survival was significantly higher at 3°C than at 6°C in 11 of 15 families measured (paired t-test, P = 0.0050). Time to hatching was 130 ± 6 d at 6°C and 156 ± 12 d at 3°C. In view of the strong effects of temperature on egg viability, the importance of cold temperatures for other life stages merits further investigation.

Early Survival of Juvenile Snowshoe Hares

Juvenile snowshoe hares (Lepus americanus) were radio—tagged at birth on one food addition grid and one control grid, to determine early juvenile survival, the effects of the food addition on survival, and proximate causes of mortality. Indices of survival were also estimated by live—trapping on these grids and on a replicate pair of grids. The overall 30—d survival rates of radio—tagged leverets were 0.46, 0.15, and 0.43 for the first, second, and third litters of the year, respectively. There were no differences between early juvenile survival on the food addition and control grids in any of the litter groups. The main proximate cause of juvenile mortality was predation by small mammalian predators, the most important being red squirrels and arctic ground squirrels. Seventy percent of early juvenile mortality occurred during the first 5 d after birth. Survival of littermates was not independent; litters tended to all live or die as a unit more often than expected by chance. Fifty—one percent of litters had no known survivors after 14 d of age. Individual survival rates were negatively related to litter size and positively related to body size at birth, and litter size was negatively correlated with body size. These correlations were most closely related to differences in life history traits among litters born at different times of the summer, rather than to trade—offs among traits within litter groups.

Larval settlement into marine soft-sediment systems: Interactions with the meiofauna

The distribution and abundance of organisms exhibiting complex life cycles, like marine invertebrates, reflect ecological processes operating at all stages in the life history. Few studies have yet considered the mortality patterns of larvae and juveniles. To test whether the permanent meiofauna play a role in macrofaunal larval site-selection, and/or if permanent meiofaunal predators or competitors and disturbers are a significant source of mortality for newly settled macrofaunal juveniles, a series of manipulations of meiofauna were performed. Densities of (1) predatory turbellarians alone, and (2) other meiofauna, were increased in small boxes placed on a holding table in a shallow subtidal habitat. Natural settlement into meiofauna manipulations was examined approximately monthly for a year. Other experiments were conducted to examine the relative importance of site-selection and post-settlement mortality and to determine if settlement was density-dependent or density-independent. Densities of spionid, cirratulid, terebellid, capitellid, and maldanid polychaetes, oligochaetes, bivalves, and amphipods were all reduced by high densities of turbellarians, and sometimes by other meiofauna. Turbellarian predation was responsible for significant post-settlement mortality, but spionids, cirratulids, terebellids, and maldanids also appeared to avoid dense turbellarian treatments. Bivalve densities were reduced by high densities of other meiofauna, probably due to their sedimentary disturbance. Syllid polychaete densities were higher in turbellarian treatments, suggesting that they select for areas with high densities of their prey (small turbellarians). The effects of meiofauna on settlement and survival were greatest in spring and summer. The results of these experiments suggest larval settlement patterns and early juvenile survival should be considered in developing general models of life history and community structure for soft-sediment systems.

Effects of extra food on Peromyscus and Clethrionomys populations in the southern Yukon.

If food supply limits density in rodent populations, the addition of supplemental food ought to increase population size. From May to September we added food on 2-hectare areas of white spruce forest in the southern Yukon. In 1977, we used oats with no measurable impact. In 1978 and 1979 we used sunflower seeds and doubled or tripled the population densities of Peromyscus maniculatus and Clethrionomys rutilus. Supplemental feeding with sunflower seeds increased juvenile production in both species, probably by increasing early juvenile survival. The breeding season ended at the same time on experimental and control areas, and the onset of maturity in juveniles was not affected by feeding. Survival of adult rodents was not improved by feeding. Immigration into sunflower seed areas was very high, and was the major factor producing the increase in population density. Body weight was not changed by feeding. Food supply is thus one factor limiting population density in these subarctic small mammals, but we do not know why supplemental food produces no more than a 2- to 3-fold effect on densities.

Survival, Growth, and Reproduction of Progeny Isolated from High and Low Density Populations of Microtus montanus

The demographic consequences of lactational deficiency, which has been hypothesized to occur during periods of physiological stress in mammals, were assessed in Microtus montanus populations under field conditions. Comparisons are made among progeny of animals in an expanding population (= U cohort), juvenile progeny removed from high-density populations and introduced with (= M cohort) and without (= I cohort) previously crowded adults, and offspring (= F1 cohort) of voles of the I cohort. Survival rate of the I cohort was higher than the M cohort. Furthermore, males of the I cohort had a significantly higher instantaneous growth rate than the M cohort. The growth rates of females in the M and I cohorts were uniformly low. Sexual maturity was delayed in males of the M and I cohorts, though the delays were not sufficient to reduce the reproductive output. There was no significant difference in the proportions of either pregnant females or reproductive activity among cohorts. Early juvenile survival was high in the populations in which the U and I cohorts resided, whereas no juveniles survived in the M cohort's population. The observed changes in demographic parameters among the cohorts do not conform to the predictions of the lactational deficiency hypothesis. Survival and age at sexual maturity were primarily affected by seasonality, whereas individual growth, early juvenile survival, and population growth were primarily affected by adult-progeny social interactions.

The demography of Synaptomys cooperi populations in eastern Kansas

Three populations of the southern bog lemming, Synaptomys cooperi, were livetrapped from November 1970 through July 1973 in eastern Kansas to determine whether populations of this microtine species undergo multiannual population cycles. Two of the populations (grids B and D) had such cycles, while one (grid A) exhibited an annual fluctuation in density. The intensity of breeding was generally higher in the summer than in the winter breeding seasons. Grids B and D had a higher percentage of males in breeding condition during two summer breeding seasons compared with grid A. Survival of the trappable adult population was usually higher in the winter than in the summer breeding seasons. Early juvenile survival paralleled changes in survival of the adults but average juvenile survival on grid A was lower than on grids B and D during the summer breeding season. A multiple regression analysis indicated that early juvenile survival is the best predictor of rate of population growth. High body weights in spring were associated with high population densities on grids B and D. Mean body weights of all three populations were higher in the summer than in the winter breeding seasons. Possible mechanisms for the noncyclicity on grid A are discussed.

Propagule Size, Number, and Dispersion Pattern in Ambystoma and Asclepias

The empirical study of life history patterns has revealed a complex of interrelated adaptations that cannot easily be explained by reference to the models of demographers. Parental investment can be expended in many ways by manipulating propagule size, propagule number, and the pattern of propagule dispersal in time and space. Each aspect of reproduction entails a balance between the benefits and cost of current reproduction versus future reproduction. Natural selection results in the pattern of reproduction that maximizes the lifetime contribution of an individual to future generations. The compromise between propagule size and propagule number is modeled by the effects of competitive challenges during the early juvenile period, dispersal mechanisms, and mechanisms of predator defense. The position of the balance is modeled by the interaction of the level of investment per clutch and the functional dependence of early juvenile survival on propagule size. The spatial pattern of egg deposition is modeled by the energetic cost of nest construction and the mortality risk to the female and the foraging efficiency of nest predators. The advantage of multiple nests is related to the variance of the number of survivors rather than the mean number of survivors. The timing and size of successive clutches is modeled in relation to the length of the growing season, the extent of parental care, female mortality patterns, and the rate at which eggs can be produced. Successive clutches may be smaller and more widely spaced in time if the rate at which females can produce eggs or female survival decreases as the season progresses. In a group of four sympatric salamanders of the genus Ambystoma the pattern of egg production can be interpreted as a suite of adaptations to the annual uncertainty of the environment in which the larvae live. The salamanders differ in egg size, egg number, egg dispersion, size at metamorphosis, length of juvenile period, size at maturity, parental investment, and adult survival rate. They all reproduce during a few weeks after the ponds have thawed, have aquatic, carnivorous larvae, and are secretive during the terrestrial adult stage. In a group of six milkweeds of the genus Asclepias seed production can be interpreted as a suite of adaptations to the risk of herbivore damage, adult survival, colony size, and the spatial and temporal pattern of opportunities for seedling establishment. The species have different growth forms, habitat distributions, flower number and arrangements, number of follicles per plant, number of seeds per follicle, and individual seed weights. All species have similar mechanisms of seed dispersal, pollinator relationships, and herbivore defense mechanisms. These examples demonstrate some fundamental differences between angiosperms and vertebrates. The sedentary habit of plants often results in extreme phenotypic plasticity. The frequent occurrence of multiple shoot units per plant permits a diversity of breeding systems that may yield genetic diversity among half-sibs produced at the same time as well as a high level of spatial (different fruits) and temporal heterogeneity in seed production. Seeds may be dispersed long distances and may lie dormant for years until conditions are promising for seedling success. Vertebrates are constrained by their bilateral body form and single reproductive system. Clutches are usually discrete and probably are generally composed of full sibs that are born at nearly the same time. A wide range of developmental diversity is possible, from a prolonged larval stage to direct development. Mobility permits a high level of habitat selection, parental control over the microhabitat of the hatchlings, and the evolution of complex behavioral systems of parental care.