Relationships of latitude,altitude, and body size to litter size and mean annual production of offspring inPeromyscus

Litter size was positively correlated with latitude and altitude but not with production of offspring or with body size in Peromyscus. Increased litter size in northern populations probably reflects shortening the breeding season by climate and not a greater mortality rate at northern latitudes compared to southern latitudes. Production of offspring was negatively correlated with body size but not with latitude, altitude, or litter size. This is probably due to larger species living longer and taking longer to mature.     

A comparative study of breeding seasonality and litter size in eleven taxa of captive lemurs (Lemur andVarecia)

Breeding records of 11 taxa of captive lemurs housed at the Duke University Primate Center (DUPC), North Carolina, were analyzed for differences in the timing of births, for the relationship between breeding season and photoperiod, and for differences in litter size. At DUPC there are significant differences in the timing of births among certain taxa, including differences among some subspecies of Lemur fulvus.However, changes in latitude result in changes in the timing of the breeding season. Lemurs moved to higher latitudes mate at lower light-dark ratios than on Madagascar. The data presented here are consistent with the following model: a photoperiodic cue initiating reproductive activity, presumably a light-dark threshold, precedes the actual mating season by approximately 2 months, with an intervening period of physiological and social preparation. On Madagascar, selection may have favored births that coincide with the end of dry seasons and the beginning of wet seasons, which results in lactation and weaning during times of resource abundance. Taxa from the north and east have the highest mean litter sizes; those from the west have the lowest.     

RETRACTED ARTICLE: Latitude affects degree of advancement in laying by birds in response to food supplementation: a meta-analysis

Food supplementation experiments have provided considerable information about the importance of resource availability in timing reproduction. Supplemented birds usually advance breeding over non-supplemented controls. Initial observations suggested that degree of advancement in studies conducted at higher latitudes was less than in those at lower latitudes. We hypothesized that birds at high latitudes are less responsive to the "supplementary" cue of food. We tested this hypothesis using a literature-based meta-analysis of 36 papers which, because several papers presented separate data sets from different years, yielded 56 "studies." We used step-wise regression to determine whether latitude, elevation, the duration of supplementation, and the migratory status of the species predicted the degree to which mean clutch initiation dates of food supplemented birds differed from non-supplemented controls (i.e., effect size = [Formula: see text]). Consistent with our predictions, there was a significant inverse relationship between effect size and latitude: elevation, migratory status, and duration of treatment contributed little to the model. Because the response of animals' reproductive systems to environmental information is mediated by the neuroendocrine system, we discuss two models: (1) the adaptive specialization hypothesis in which higher latitude species that experience a relatively short breeding season have evolved a reliance on photic cues while exhibiting reduced sensitivity to non-photic cues; and (2) the conditional plasticity hypothesis in which an individual might show a marked response to non-photic information if it lived at low latitudes, but be largely driven by photic cues, endogenous rhythms, or both to the relative exclusion of non-photic information if it lived at higher latitudes.     

Large-scale intraspecific variation in life-history traits of European freshwater fish

Aims To test the magnitude and direction of the effects of large‐scale environmental factors (latitude and habitat type: lotic or lentic) on the intraspecific variations in multiple life‐history traits, across multiple European freshwater fish species. To test the relevance of defining species traits by quantifying the magnitude of interspecific vs. intraspecific variability in traits. Location Europe. Methods We obtained estimates of 11 fish traits from published sources for 1089 populations of 25 European freshwater fish species. Traits were: longevity, maximal length, growth rate, asymptotic length, mortality rate, age and length at maturation, fecundity, egg size, gonadosomatic index, and length of breeding season. We described population habitats by latitude and habitat type (lotic or lentic), when available. For each species we tested the combined effect of latitude and habitat type on the intraspecific variation of each trait using analysis of covariance (ancova ). We compared the intraspecific variation in traits with the variation between species using an analysis of variance (anova ) for each trait, all species pooled. Results We found a consistent effect in direction of latitude on six traits, but we showed that this effect is not always significant across species. Higher‐latitude populations often grew more slowly, matured later, had a longer life span and a higher maximal and asymptotic length, and allocated more energy to reproduction than populations at lower latitudes. By contrast, we noted only a slight effect of habitat type on the intraspecific variation in traits, except for Salmo trutta. All traits varied significantly between species. However, traits such as growth rate, mortality rate and length of breeding season varied more between populations than between species, whereas fecundity and traits associated with body length varied more between species. Main conclusions Latitude, in contrast to habitat type, is an important factor influencing several traits of geographically widely dispersed populations of multiple European freshwater fish species. Species traits that vary more between species than between populations are attractive variables for understanding and predicting the responses of stream fish communities to their environment.     

Latitudinal pattern in body size in a cockroach,Eupolyphaga sinensis

Body size of insects with flexible life cycles is expected to conform to the saw‐tooth model, a model in which the relationship between size and developmental time depends on length of the growing season. In species with high variability in terms of voltinism, however, more complex patterns can be expected. Few empirical studies have demonstrated the existence of such relationships, or whether climatic factors contribute to these relationships. In this study, we investigated the geographic variation in body size of the Chinese cockroach, Eupolyphaga sinensis Walker (Blattaria: Polyphagidae), which has a variable life cycle length. The sizes of adults – collected from 14 localities ranging from temperate to subtropical zones in China – were measured, using body length, body width, and pronotum width as parameters. The relationship between size, latitude, and climate factors (encompassing 10 variables) was then investigated. We found that the body size of E. sinensis varied considerably with latitude: cockroaches were larger at low and high latitudes, but smaller at intermediate latitudes. Thus, the relationship between climate and body size conformed to a saw‐tooth pattern. Results indicate that two factors were significantly associated with body size clines: season length and variability in life cycle length. Our results also demonstrated that climatic factors contribute to latitudinal clines in body size, which has important ecological and evolutionary implications. It can be expected that global climate change may alter latitudinal clines in body size of E. sinensis.     

Accipiter hawks of the Laurentian Upland and the Interior Plains undertake the longest migrations: insights from birds banded or recovered in Veracruz,Mexico

Bird banding has allowed us to understand diverse aspects of the life histories of migratory raptors. However, most banding stations are located at northern latitudes so what we know about the movements of these raptors is biased toward higher latitudes, primarily from Canada and the United States, leaving important gaps in our knowledge of their movements at lower latitudes. Our objective was to describe the migratory movements of Sharp-shinned (Accipiter striatus) and Cooper’s (A. cooperii) hawks based on banding and recapture records of birds that migrate through Veracruz, Mexico. More specifically, we sought to determine their breeding, migration, and non-breeding locations, estimate their migration distances, and contribute to a better understanding of their migration patterns. With a total of 80 records, we calculated migration distances and used Kernel Density Estimation analyses to identify where these hawks were recaptured or recovered by season. The distribution of recaptures and recoveries largely coincided with breeding locations in the Laurentian Upland and the Interior Plains physiographic regions. All migration records follow a trajectory that extends from the midwestern United States to the Gulf coastal plain of Mexico. The mean breeding season migration distance to Veracruz was 3374 km (a difference of 27 degrees of latitude) for Sharp-shinned Hawks and 2926 km (a difference of 25 degrees of latitude) for Cooper’s Hawks. Our non-breeding records indicate that populations of Accipiter hawks from these North American populations migrate the longest distances to reach Central America, the southernmost distribution of their migratory populations. Distances covered by both species represent round-trip migrations that may be as long as 10,000 km. Our results support those of previous studies and illustrate how continental physiography influences the migration routes, migratory behavior, and migratory connectivity of these hawks.     

Latitudinal distribution, migration, and testosterone levels in birds

Tropical bird species usually have lower testosterone (T) levels during breeding than temperate species. However, the potential mechanisms behind the positive interspecific correlation between T and latitude remain unexplored. In a comparative study of more than 100 bird species, we examined whether social constraints during male-male competition arising from migration and breeding synchrony are responsible for the latitude effects. Species that breed at higher latitudes are more likely to migrate and experience more intense intrasexual competition upon spring arrival than nonmigrant species from lower latitudes. Additionally, species from higher latitudes cope with shorter breeding seasons and thus with more synchronous breeding, which selects for high T titers via increased male-male conflicts. Accordingly, peak T levels were associated with migration and the duration of the egg laying period that reflects breeding synchrony. Because migration and breeding synchrony were related to latitudinal distribution, they appear to be important components of the latitude effects on T. A multivariate model controlling for covariation of predictor variables revealed that latitude remained the strongest predictor of peak T. Therefore, selection due to migration and breeding synchrony may partially cause the latitude effect, but other geographically varying factors may also play a role in mediating peak T levels at different latitudes.     

Sex,reproductive cycle and variations in the fecundity of the family schilbeidae (Osteichthyes : Siluriformes) in Lake Kainji,Nigeria.

The sex, reproductive cycle and variations in the fecundity of the family Schilbeidae (Osteichthyes : Siluriformes) in Lake Kainji, were investigated. Sexual differences in size and morphology were found to exist in all species. Sex ratio varied with species and season. There were more females than males in the population. Size at maturity varied from species to species with the males attaining maturity at a slightly lower length than the females. Breeding condition was attained mainly during the rains in Eutropius niloticus, Schilbe mystus and Siluranodon auritus and in the dry and rainy seasons in Physailia pellucida. Spawning occurred once during the breeding season in E. niloticus and S. mystus; and more than once during the prolonged breeding season in P. pellucida. Condition factors did not show any correlation with maturation of gonads. Fecundity was found to vary from species to species.     

Latitudinal gradients in some,but not all,avian life history traits extend into the Arctic

Latitudinal variation in avian life history strategies is well documented. Clutch size and nest success tend to increase with latitude, whereas longevity and developmental periods have been argued to decrease with latitude. However, these patterns are largely based on interspecific comparisons of species breeding at tropical and temperate latitudes. We compared the life history of Yellow Warblers Setophaga petechia breeding in arctic habitat at the northern extent of their range, in Inuvik, NWT (68°N), Canada, with those breeding in temperate habitat in Revelstoke, BC (50°N), and use data from 21 populations spanning 0–68°N to evaluate latitudinal trends in life history traits from tropical to arctic habitats. Females breeding in Inuvik laid first clutches that were slightly (although not significantly) larger and had higher nest success, which resulted in higher annual productivity compared with their low- latitude counterparts. Apparent adult survival rates were only marginally lower in Inuvik than in Revelstoke, whereas incubation and nestling periods in the arctic were similar to our temperate site. When comparing life history traits across the Yellow Warbler breeding range, we observed increases in clutch sizes and nest success with increasing latitude that appeared to be associated with declines in adult survival, though this relationship was weakened by the addition of our arctic site. We detected more moderate declines in incubation and nestling periods with increasing latitude. As we observed latitudinal variation in some life history traits, but not a consistent transition of traits associated with a shift from a slow to fast life history from tropical to arctic latitudes, our study suggests that the expectation for a general shift in life history traits may be over-simplified.     

Old‐field grassland successional dynamics following cessation of chronic disturbance

Question: Does increasing Festuca canopy cover reduce plant species richness and, therefore, alter plant community composition and the relationship of litter to species richness in old‐field grassland? Location: Southeastern Oklahoma, USA. Methods: Canopy cover by species, species richness, and litter mass were collected within an old‐field grassland site on 16, 40 m × 40 m plots. Our study was conducted during the first three years of a long‐term study that investigated the effects of low‐level nitrogen enrichment and small mammal herbivory manipulations. Results: Succession was altered by an increase in abundance of Festuca over the 3‐yr study period. Species richness did not decline with litter accumulation. Instead, Festuca increased most on species‐poor plots, and Festuca abundance remained low on species‐rich plots. Conclusions: Festuca may act as an invasive transformer‐species in warm‐season dominated old‐field grasslands, a phenomenon associated more with invasions of cool‐season grasses at higher latitudes in North America.     

Habitat Preference, Reproduction and Diet of the Earthworm Eel, Chendol keelini (Teleostei: Chaudhuriidae)

The ecology of the earthworm eel, Chendol keelini, was studied in the field over a period of nine months. In addition this information was supplemented by aquarium observations. The species was most abundant in pools where it was associated with leaf litter and mats of fine tree roots along the banks. It fed on benthic invertebrates, especially chironomid and ephemeropteran larvae. C. keelini is sexually dimorphic; adult males develop a headhump and grow to a larger size than females. Reproduction was seasonal; the reproductive phase coincided with the wet season and lasted for several months. Fecundity was around 40 eggs per clutch. The eggs were spherical, between 1.2 and 1.5mm in diameter, and possessed a pair of long filaments for adhesion to the substrate. Females probably spawned more than once during the breeding season. The length frequency distributions and juvenile growth suggest that C. keelini is a short-lived species that matures during the first year with few individuals surviving to the second breeding season.     

川西高山林线三种灌木凋落叶分解中的无脊椎动物多样性

以无脊椎动物为主体的土壤动物是影响凋落物分解的重要生物因素,对维持陆地生态系统物质循环和能量流动具有重要作用。高山林线交错带是高山植被垂直带谱中重要的过渡区域,拥有比相邻生态系统更高的生境复杂性和物种多样性。林线上温度波动和冻融循环频率显著高于针叶林,为了了解林线交错带上环境差异对凋落物分解过程中的土壤动物群落结构和多样性的影响,采用凋落物分解袋的方法,于高山生态系统的两个主要时期,即雪被末期和生长季末期,研究了林线主要代表性灌木——高山柳(Salix cupularis)、高山杜鹃(Rhododendron lapponicum)和红毛花楸(Sorbus rufopilosa)凋落叶分解的土壤动物多样性特征。结果表明:凋落物中的无脊椎动物群落多样性及个体、类群密度随物种、海拔梯度和季节而变化,且季节差异对无脊椎动物多样性的影响比物种和海拔梯度更显著。3个因子的交互作用不仅影响土壤动物群落多样性和均匀度,而且影响群落个体密度和类群密度。雪被末期,凋落物中的无脊椎动物多样性指数H、均匀度指数J及丰富度指数D以针叶林最高,优势度指数C以林线最高;生长季节末期的无脊椎动物类群密度和个体密度显著高于雪被末期。总体上,凋落物中的无脊椎动物群落丰富度以生长季末期最高,林线较针叶林丰富。这意味着,未来气候变暖情景下,灌丛密度增加,凋落物输入量增大,可能导致无脊椎动物多样性增加。     

Sexual selection in the barn swallow (Hirundo rustica). V. Geographic variation in ornament size

Models of sexual selection in a cline predict the patterns of clinal variation in female mate preference and male secondary sexual characters. These predictions were tested for the nominate subspecies of the barn swallow Hirundo rustica which demonstrates clinal variation in morphology, with several characters in both sexes showing increasing size at higher latitudes. Sexual size dimorphism in the length of the tail ornament and the short, central tail feathers increase with increasing latitude while size dimorphism in other morphological characters is independent of latitude. The main reason for the two divergent patterns of sexual size dimorphism appears to be the higher foraging cost of having a long tail ornamental at low latitudes. The control of development decreases with increasing latitude as demonstrated by an increasing latitudinal cline in fluctuating asymmetry of tail length. Phenotypic variance in tail length increases with latitude in males, but not in females, as shown by the coefficients of variation. Clinal variation in morphology is not due to natural selection associated with a latitudinal increase in the distance between breeding and wintering areas. The geographic patterns of morphological variation suggest that the tail character has diverged geographically as a result of a sexual process of reliable signalling.     

A large‐scale latitudinal pattern of life‐history traits in a strictly univoltine damselfly

1. Variation in thermal conditions and season length along latitudinal gradients affect body size‐related traits over different life stages. Selection is expected to optimise these size traits in response to the costs and benefits. 2. Egg, hatchling, larval and adult size in males and females were estimated along a latitudinal gradient of 2730 km across Europe in the univoltine damselfly Lestes sponsa, using a combination of field‐collection and laboratory‐rearing experiments. In the laboratory, individuals were grown in temperatures and photoperiod simulating those at the latitude of origin, and in common‐garden conditions. 3. The size of adults sampled in nature was negatively correlated with latitude. In all populations the females were larger than the males. Results from simulated and common‐garden rearing experiments supported this pattern of size difference across latitudes and between sexes, suggesting a genetic component for the latitudinal size trend and female‐biased size dimorphism. In contrast, hatchling size showed a positive relationship with latitude, but egg size, although differing between latitudes, showed no such relationship. 4. The results support a converse Bergmann cline, i.e. a negative body size cline towards the north. This negative cline in body size is probably driven by progressively stronger seasonal time and temperature constraints towards the higher latitudes and by the obligate univoltine life cycle of L. sponsa. As egg size showed no relationship with latitude, other environmental factors besides temperature, such as desiccation risk, probably affect this trait.     

BREEDING SEASONS OF BIRDS IN DECIDUOUS WOODLAND AT ZIMBABWE,RHODESIA, FROM 1970 TO 1974

Vernon, C. J. 1978. Breeding seasons of birds in deciduous woodland at Zimbabwe, Rhodesia, from 1970 to 1974. Ostrich 49:102-115.

The birds in Brachystegia woodland bred in the spring and 98% of 1645 breeding records occurred between September and November. 90% of the records, and 43 of the 71 breeding species, were of insectivorous passerines. The breeding seasons of individual species lasted for between less than two months to more than three months, and their peak breeding periods varied between early September and the middle of October. The breeding season started earliest in 1974 and latest in 1973, and the start of two species was related to the timing of leaf emergence of the dominant tree in the woodland and to rainfall the previous rainy season. Food supply may be the proximal factor influencing the onset of breeding.     

Annual cycles in Jamaican forest birds

The annual cycles of forest birds in Jamaica were found to be very similar to those at higher latitudes. Most species bred between March and September, though a few possibly breed throughout the year, especially in cultivated areas. Primary moult followed immediately after breeding, and in some species was apparently arrested to allow a further breeding attempt. Several species were fatter outside the breeding season than during it, and this is interpreted as "winter fattening" comparable to that found in many birds at higher latitudes. Weights varied little but individuals retrapped were usually heavier outside the breeding season. In some species the first complete moult took place at the end of the first year, implying that the birds do not breed until at least two years old.     

SHORT NOTES

Earlé, R. A. 1981. Factors governing avian breeding in Acacia savanna, Pietermaritzburg, Part 3: Breeding success, recruitment and clutch size. Ostrich 52:235-243.

The clutch size and breeding success of eight species of birds were monitored over a two year period in Acacia savanna. The mean clutch size fluctuated within the breeding season and four patterns of clutch size variation were noted. A smaller proportion of large clutches were laid in the 1979 season when less food was available. Breeding success was higher in the dry 1979 season but fewer breeding attempts were made and the overall recruitment was thus lower. At the peak of the breeding season, in mid-November, breeding success was at its lowest. Predation on nests was the greatest factor reducing breeding success although rain and strong winds affected some species.     

The fiddler crab,Minuca pugnax,follows Bergmann's rule

Bergmann's rule predicts that organisms at higher latitudes are larger than ones at lower latitudes. Here, we examine the body size pattern of the Atlantic marsh fiddler crab, Minuca pugnax (formerly Uca pugnax), from salt marshes on the east coast of the United States across 12 degrees of latitude. We found that M. pugnax followed Bergmann's rule and that, on average, crab carapace width increased by 0.5 mm per degree of latitude. Minuca pugnax body size also followed the temperature–size rule with body size inversely related to mean water temperature. Because an organism's size influences its impact on an ecosystem, and M. pugnax is an ecosystem engineer that affects marsh functioning, the larger crabs at higher latitudes may have greater per‐capita impacts on salt marshes than the smaller crabs at lower latitudes.     

Testing generalizations about latitudinal variation in reproduction and recruitment patterns with sicyoniid and caridean shrimp species

Summary

Study of latitudinal variation in seasonality of reproduction and recruitment of benthic marine invertebrates is useful in generating and testing hypotheses about causal factors acting on reproduction such as temperature and larval food supply that might be altered by changes in world climate. Analysis of latitudinal variation in reproductive patterns might be made with comparisons (a) among species with a common phylogenetic history from different latitudes and habitats and (b) among phylogenetically different taxa from the same location. Hypotheses on variation of reproductive seasonality with latitude are tested here with results of a study on nine species of caridean and two species of sicyoniid shrimp sampled from a tropical seagrass meadow in Puerto Rico. Breeding condition was determined by the presence or absence of incubated embryos (carideans) and the state of ovarian development in both carideans and sicyoniids. Recruitment was estimated from the percentage of individuals of monthly population samples in the juvenile size classes. Comparison of reproductive patterns among tropical, subtropical, and cool temperate Sicyonia spp. supports the paradigm of continuous reproduction in the tropics with increased restriction of breeding season with an increase in latitude. A greater intensity of breeding effort appears to accompany the shorter breeding period associated with an increase in latitude. At the tropical site most females of all caridean species carried embryos during all months of the year. With the onset of sexual maturity, caridean females produced consecutive broods for the rest of their relatively short (< 6 month) life span. In both sicyoniid and caridean species, recruitment occurred throughout the year but was highly variable, i.e., episodic rather than truly continuous or seasonal. Patterns of recruitment were highly concordant among but not between sicyoniid and caridean species, indicating that different sets of environmental factors controlled recruitment in the two groups. It is suggested that simultaneous study of adult reproduction and larval ecology is necessary to understand patterns of reproduction and recruitment. Coordinated effort on a global scale in studying latitudinal variation in reproduction and recruitment is suggested in order to predict the consequences of climate change on commercially and ecologically important marine invertebrate species.     

Is the proportion of clonal species higher at higher latitudes in Australia?

We provide a large‐scale quantification of the relationship between latitude and the proportion of species with clonal reproduction. Parasite pressure is thought to be higher at low latitudes, while abiotic stress is thought to be higher at high latitudes. We therefore predicted that there would be a higher proportion of clonal species at high latitudes than at low latitudes. We collected data of 4386 native seed plant species from 446 genera and 99 families present in ABRSFlora of Australia. Species' occurrence records were taken from the Atlas of Living Australia, including 817 450 species‐site combinations spanning 34.5° of latitude. Logistic regression showed that the proportion of clonal species significantly increased with latitude, rising from 3.3% clonal species at 9.25°S to 26.7% clonal species at 43.75°S. The overall average proportion of clonal species in Australian seed plants was 9.4%. This study adds to our growing understanding of dramatic latitudinal gradients in the way plants grow and reproduce. It also reveals that Australian vegetation contains a relatively low proportion of clonally reproducing species.