Relative roles of density-dependent and density-independent factors in population dynamics of British deer

It has become increasingly clear that both density-dependent and density-independent factors may influence the dynamics of mammalian populations; it remains more difficult, however, to determine which factors may play the more significant role in influencing population number in any particular case. In this paper we review published and unpublished data in an analysis of the various factors affecting population size and trend in three European species of deer: Red Deer ( Cervus elaphus ), Fallow Deer ( Dama damd ) and Roe Deer ( Capreolus capreolus). We select these species deliberately because they span a range of body size and reproductive strategy - it seems that different demographic parameters might thus play different roles in the dynamics of the three-which may also be differentially sensitive to the effects of density-dependent and density-independent factors. For each species we examine the available evidence to determine the relative roles and effects of density-dependent feedback mechanisms and density-independent factors such as climate on recruitment and mortality.
Despite differences in bionomic strategy between Red Deer (as essentially a K -strategist) and the more r-selected Roe, few differences emerge between the three species in the relative roles of density-dependent and density-independent factors - or of the stage at the life cycle at which each factor may act. Overall, however, it is clear that variation in density-independent factors, such as climate, appears primarily to affect levels of mortality within a population, while effects of density are particularly marked in relation to changes in recruitment.     

Retinotectal Connexions of a Heterotopic Eye

THE mechanisms which cause the formation of specific synaptic connections in the nervous system are rather obscure. The development of specific connexions between eye and brain indicates a stage-dependent functional specification of the retina¹ which allows the retina to form predictable, specific connexions with the optic tectum, but the manner in which optic nerve fibres terminate in the tectum and the mechanisms which restore the visual projection after optic nerve regeneration are as yet not fully determined².     

Gametogenesis and Embryogeny of Tamarix ericoides Rottl

1. The haploid chromosome number in Tamarix ericoides Rottl., reportedfor the first time, is twelve.
2. The archesporial cell is single,rarely double.
3. There is no tetrad formation, division of themegaspore mother-cell;instead, a four nucleate embryo-sac results.
4. The nuclei are originally arranged in a cruciform type, butlater form a I+3 arrangement.
5. As a result of the third division,the embryo-sac is again four-nucleate,with two haploid nucleiat the micropylar end and two triploidnuclei at the chalazalend.
6. The cells of the embryo-sac are formed at the end ofthe fourthdivision, the embryo-sac thus representing the sixteennucleatecondition.
7. The development of the embryo-sac of Tamarixericoides conformsto the Fritillaria-type.
8. The endospermis free nuclear, and the embryo is characteristicin developinga massive suspensor and a large pad of cellulartissue fromthe proximal cell.
9. Double embryo-sacs and the occurrence ofpolyembryony are reportedfor the first time in the family.

     

Effect of host plant resistance and chemical control of the head bug, Calocoris angustatus Leth., on grain quality and seedling establishment in sorghum

The sorghum head bug, Calocoris angustatus Lethiery (Hemiptera: Miridae), is one of the most important pests of grain sorghum in India. Studies were conducted to quantify the effect of head bug damage on grain quality and seedling establishment on head bug-resistant cultivars (IS 17610 and IS 21443), a moderately susceptible cultivar (IS 9692), and a susceptible commercial cultivar (CSH 11). Differences in 1000-grain mass, seed germination and percentage of floaters were significant between protected and unprotected plots in CSH 11 and IS 9692, but not in IS 17610 and IS 21443. Grain damage ratings were significantly lower in IS 17610 than in IS 9692 and CSH 11 across different protection levels. Head bug-damaged grain had greater protein content than the undamaged grain, possibly because of depletion in starch, and a marginal increase in soluble sugars. Amounts of proline and tyrosine were greater in the bug-damaged grain than in the undamaged grain, while the reverse was true for aspartic acid, methionine, leucine and lysine. Head bug damage also increased the tannin content in IS 9692 (which is a high-tannin genotype). Moisture regimes and insecticide protection levels significantly affected seedling emergence. Seedling emergence of CSH 11 was lower than that in IS 17610. In the latter genotype, the differences between protected and unprotected plots were not significant. Head bug damage thus not only leads to quantitative loss in grain yield, but also spoils the grain quality and renders the grain unfit for seed purposes. These qualitative effects should be taken into account while estimating losses due to bug damage and determining economic thresholds.     

Copper Nutrition of Sugarbeet

Sugarbeet (Beta vulgaris L.) plants were grown in refined sandat graded levels of copper ranging from acute deficiency (0.000325µg Cu cm^–3) to excess (65 µg Cu cm^–3).Visible effects of copper deficiency appeared up to 0-00065µg Cu cm^–3and depression in growth up to 00065µCucm^–3. Copper deficiency decreased the concentrations ofDNA and RNA and the activities of polyphenol oxidase, cytochrome-coxidase, catalase and aldolase; and it increased the activitiesof peroxidase, ribonuclease and acid phosphatase in leaves.The maximum sucrose concentration in roots was obtained at 0-65µCucm^–3 Twenty four h after infiltration of a solution of 65µCucm^–3into copper deficient leaves, the activities of cytochrome-coxidase and peroxidase had increased even in the presence ofcycloheximide but that of polyphenol oxidase increased onlyin the absence of this inhibitor. Key words: Beta vulgaris, Cu deficiency: Enzymes