Analysis of sibling cannibalism among pike,Esox lucius,juveniles reared under semi-natural conditions

Synopsis Sibling cannibalism in pike, Esox lucius, larvae and juveniles living in outdoor rearing ponds was studied using stomach contents analysis. For the two initial densities tested (6 and 18 larvae m^–2, equivalent to 12 and 36 larvae m^–3), cannibalism was non-existent during the larval period (13 to 35 mm total length) and was observed only during the juvenile stages. Initial density of larvae influenced both the date of first detection of cannibalistic individuals and the rate of development of cannibalism in the population. At initial stocking densities of 18 larvae m^–2 (36 larvae m^–3), cannibalism was observed from 21 days after the start of exogenous feeding (mean total length: 60 mm) onwards. At a mean total length of 100 mm and for initial stocking densities of 6 and 18 larvae m^–2, (12 and 36 larvae m^–3), the average proportions of cannibals in the populations of juveniles were 7.8% and 41.3% and the cannibals accounted for 15.5% and 65.9% of the total pike biomass, respectively. In stomachs of cannibals, young pike were the dominant prey in terms of weight. Dry weights of invertebrate-prey were lower in cannibals than in non-cannibals of similar size. Cannibalism among pike juveniles was characterized by the prey being swallowed whole and head first in the vast majority of cases. There was a strong positive correlation between predator and prey size and the mouth size of a cannibal was found to be an important constraint determining maximum victim size. The overall mean ratio of pike prey length to pike cannibal length was 66.2% and the average ratio of prey head depth to predator mouth width amounted to 87.6%. Prey size selection could be demonstrated for several length-groups of cannibals. These results are compared with the characteristics of early cannibalism in other fish species.     

Importance of communal foraging grounds outside the reed marsh for breeding great reed warblers

Foraging habitat selection of breeding great reed warblers was studied at a shore of Lake Biwa. The foraging grounds of parent warblers during the nesting period were not restricted to the breeding territory of the reed marsh, their nestling habitat. The paddy field outside the reed marsh was used communally by them throughout the breeding season. Females with early stage nestlings did not visit the paddy field whereas when nestlings were older than 3 days, more than half of their total food was collected there. Females with nests adjacent to the paddy field tended to exploit the paddy field more often than those with nests distant from it. Monogamously mated females tended to exploit the paddy field more often than polygynously mated females. Food collected in the paddy field was larger than that in the reed marsh and parent birds were prepared to travel longer distances to exploit the rich source of food in the paddy field. The importance of the communal foraging ground outside the reed marsh as a background of the polygynous mating system of this species is discussed.     

Fish size and habitat depth relationships in headwater streams

Summary Surveys of 262 pools in 3 small streams in eastern Tennessee demonstrated a strong positive relationship between pool depth and the size of the largest fish within a pool (P<0.001). Similarly, the largest colonizers of newly-created deep pools were larger than the colonizers of shallow pools. We explored the role of predation risk in contributing to the bigger fish — deeper habitat pattern, which has been noted by others, by conducting five manipulative field experiments in two streams. Three experiments used stoneroller minnows (Campostoma anomalum); one used creek chubs (Semotilus atromaculatus); and one used striped shiners (Notropis chrysocephalus). The stoneroller experiments showed that survival of fish approximately 100 mm in total length (TL) was much lower in shallow pools (10 cm deep) than in deep (40 cm maximum) pools (19% versus 80% survival over 12 d in one experiment) and added cover markedly increased stoneroller survival in shallow pools (from 49% to 96% in an 11-d experiment). The creek chub experiment showed that, as for stonerollers, pool depth markedly influenced survival: the chubs survived an average of 4.9 d in shallow pools and >10.8 d in deep pools. In the striped shiner experiment in shallow artificial streamside troughs, no individuals 75–100 mm TL survived as long as 13 d, where-as smaller (20–25 mm) fish had 100% survival over 13 d. The results of the experiments show that predation risk from wading/diving animals (e.g., herons and raccoons) is much higher for larger fishes in shallow water than for these fishes in deeper water or for smaller fish in shallow water. We discuss the role of predation risk from two sources (piscivorous fish, which are more effective in deeper habitats, and diving/wading predators, which are more effective in shallow habitats) in contributing to the bigger fish — deeper habitat pattern in streams.     

Trophic interactions and habitat segregation between competing Daphnia species

Summary Two commonly coexisting species of Daphnia segregate by habitat in many stratified lakes. Daphnia pulicaria is mostly found in the hypolimnion whereas D. galeata mendotae undergoes diel vertical migration between the hypolimnion and the epilimnion. I examined how habitat segregation between these two potentially competing species might be affected by trophic interactions with their resources and predators by performing a field experiment in deep enclosures in which I manipulated fish predation, nutrient levels, and the density of epilimnetic Daphnia. The results of the experiment indicate that habitat use by D. pulicaria can be jointly regulated by competition for food from epilimnetic Daphnia and predation by fishes. Patterns of habitat segregation between the two Daphnia species were determined by predation by fish but not by nutrient levels: The removal of epilimnetic fish predators resulted in higher zooplankton and lower epilimnetic phytoplankton densities and allowed D. pulicaria to expand its habitat distribution into the epilimnion. In contrast, increased resource productivity resulted in higher densities of both Daphnia species but did not affect phytoplankton levels or habitat use by Daphnia. The two species exhibit a trade-off in their ability to exploit resources and their susceptibility to predation by fish. D. g. mendotae (the less susceptible species) may thus restrict D. pulicaria (the better resource exploiter) from the epilimnion when fish are common due to lower minimum resource requirements than those needed by D. pulicaria to offset the higher mortality rate imposed by selective epilimnetic fish predators. D. g. mendotae does not appear to have this effect in the absence of fish.     

Prediction of F3 row performance from F2 individual plant data in oats

Summary Parameters estimated from a Gardner-Eberhart analysis of the F₂ generation of a six-parent diallel in oats (Avena sativa L.) were used to compare methods for predicting the performance of F₃ row plots. The prediction methods were: (1) individual F₂ plant performance (F2I), (2) parent average plus F₂ plot deviations (PF2), (3) parent average plus weighted F₂ plot deviations (PF2P), (4) best linear unbiased prediction (BLUP) of parent average plus F₂ plot deviations (BPF2), and (5) BLUP plus weighted F₂ deviations (BF2). The F₂ single-plant traits used for prediction were biological yield to predict F₃ biological yield, whole plant and primary tiller grain yield for prediction of F₃ grain yield, and whole plant and primary tiller harvest index (HI) to predict F₃ HI. Prediction methods were evaluated by correlations between predicted and observed F₃ performance. Prediction methods and traits for which correlations were greater than for F2I included: BF2 for biological yield, PF2, PF2P and BF2 for whole plant grain yield, PF2, BPF2, and BF2 for primary tiller grain yield. None had a correlation significantly greater than F2I for either measure of HI, where heritability was large. PF2 is the recommended method for traits with low heritability because of its simplicity and because it had the largest or nearly the largest correlation for each of the yield traits. F2I is the recommended method for traits with larger heritability.Contribution No. 8821 of the U.S. Regional Pasture Research LaboratoryDeceased     

What is this stuff called fitness?

This paper considers a variety of attempts to define fitness in such a way as to defend the theory of evolution by natural selection from the criticism that it is a circular argument. Each of the definitions is shown to be inconsistent with the others. The paper argues that the environment in which an animal evolves can be defined only with respect to the properties of the phenotype of the animal and that it is therefore not illuminating to try to explain the phenotypic properties of the animal in terms of adaptation to an environment that is defined by those very properties. Furthermore, since there is no way that the environment can be defined independently of the presence of the animal there is no way that the quality of an animal can be assessed; and there can be no objective criteria by whichany form of selection can be carried out, therefore there can be no criteria by whichnatural selection can be carried out. It is proposed that fitness is nothing more than the production of offspring, that this is a phenotypic property like all the others, and if it is heritable then the offspring of the parents that produce the most offspring will themselves produce the most offspring, and that in principle it is impossible to account for this in terms of the other phenotypic properties of the fittest animals except by circular argument. Differential rates of reproduction are the causes of evolution and the phenotypic causes are strictly inexplicable.     

Ejaculate size varies with socio-sexual situation in an insect

Abstract.

• 1 Males operate within a finite energy budget and cannot produce limitless supplies of sperm. On the other hand, when a female mates with a second male while still containing fertile sperm from a rival male, selection should favour the male that inseminates more sperm. Optimal strategy should thus be for males to exercise discretion in the allocation of sperm to individual females. Assuming the outcome of sperm competition to be based on either the raffle or kamikaze principles, the sperm competition hypothesis predicts a positive association between the probability that the sperm will find themselves in competition with sperm from rival males and the number of sperm inseminated.
• 2 The beetle, Tenebrio molitor L., behaves in accordance with this hypothesis. Males accompanied by a rival male before and during mating inseminate more sperm per ejaculate than unaccompanied males. Accompanied males are also faster to initiate mating and more likely to show post-copulatory guarding. Adjustment of number of sperm inseminated was shown by males subjected to both long-term (5 days) and short-term (5 min) exposure to potential intrasexual competitors. Individual males exposed to both levels also demonstrated the ability to adjust their ejaculate according to socio-sexual situation.
• 3 We conclude that male T.molitor adjust the number of sperm they inseminate according to some perception of the risk of sperm competition.

     

Habitat selection and subsequent reproductive success in the beaugregory damselfish

Synopsis Male beaugregory damselfish,Stegastes leucostictus, were provided with three types of artificial breeding structures to determine if they change habitats based on past or future reproductive payoffs. All three site types quickly lured males away from their natural sites. In comparison to those living on natural sites, those using artificial sites were less likely to move to different areas and had a higher reproductive success. When given no choice, male reproductive success was correlated to structural type. A second experiment provided males with an additional structure after using the intermediate quality type for 2 months. Males would often initially use both sites but would eventually shift their spawning activity to the new site if it was of the same quality or better than the old one. However, males would not move if the new site was of inferior quality. When given a new site identical to the initial one, approximately half of the males shifted to the new site. There was no evidence that reproductive performance influenced a male's decision to use a new site.     

藏马鸡(Crossoptilon crossoptilon)的繁殖生态研究

藏马鸡是典型高山地牺雉类,见于海拔3,500—3,900米的针叶林带。自4月中至7月底为繁殖期。一“夫”配一“妻”。营巢于海拔3,544—3,790米的岩洞、灌丛中或倒木下。共发现4巢,3巢已被破坏,成功率25％。近年来,由于过渡砍伐森林,天敌的伤害,自身弱点(繁殖率低,成熟期长(3年左右)以及其他因素,藏马鸡的数量日趋减少,正面临绝种的厄运。必须及时地采取有效保护措施。     

绿尾虹雉生态学研究

绿尾虹雉Lophophorus lhuysti生态和生物学研究是中国科学院重点科研课题——“中国珍稀濒危难类生态生物学”——部分工作。 本文为作者对绿尾虹雉所作的生态和生物学系统研究首次报道。绿尾虹雉主要牺息于海拔3,500—4,000米亚高山灌丛和草甸。杂食性鸟类,以植物性食物为主,亦食昆虫。营巢于岩洞或灌丛地面上,每窝产3—4,多达11枚卵。种群密度1.32—1.58只/km~2。目前数量急剧下降,处于濒危,急待保护。