RESUMO
Conservationists often advocate for landscape approaches to wildlife management while others argue for physical separation between protected species and human communities, but direct empirical comparisons of these alternatives are scarce. We relate African lion population densities and population trends to contrasting management practices across 42 sites in 11 countries. Lion populations in fenced reserves are significantly closer to their estimated carrying capacities than unfenced populations. Whereas fenced reserves can maintain lions at 80% of their potential densities on annual management budgets of $500 km(-2) , unfenced populations require budgets in excess of $2000 km(-2) to attain half their potential densities. Lions in fenced reserves are primarily limited by density dependence, but lions in unfenced reserves are highly sensitive to human population densities in surrounding communities, and unfenced populations are frequently subjected to density-independent factors. Nearly half the unfenced lion populations may decline to near extinction over the next 20-40 years.
Assuntos
Carnívoros , Conservação dos Recursos Naturais/métodos , Leões , Densidade Demográfica , Animais , Conservação dos Recursos Naturais/economia , Gana , Humanos , Namíbia , Dinâmica Populacional , Setor Privado , África do SulRESUMO
Rat cerebral cortex synaptosomes synthesise prostaglandins, and analysis by gas chromatography-mass spectrometry revealed that of the prostaglandins quantified PGD2 (10.9 ng/mg protein) was produced in highest concentration. Treatment with high potassium or veratrine caused release of putative amino acid transmitters, but not of prostaglandins, and prostaglandins D2 and E2 were unable to stimulate release of amino acids. The release of putative amino acid transmitters, evoked by high potassium levels, was not inhibited by these prostaglandins. Prostacyclin receptors could not be identified on synaptosomes by radioligand binding techniques.
Assuntos
Aminoácidos/metabolismo , Córtex Cerebral/metabolismo , Prostaglandinas D/farmacologia , Prostaglandinas E/farmacologia , Prostaglandinas/farmacologia , Sinaptossomos/metabolismo , Animais , Dinoprostona , Epoprostenol/metabolismo , Feminino , Técnicas In Vitro , Ratos , Ratos Endogâmicos , Ácido gama-Aminobutírico/metabolismoAssuntos
Aminoácidos/análise , Córtex Cerebral/fisiologia , Corpo Estriado/análise , Neurotransmissores/análise , Animais , Sítios de Ligação , Feminino , Glutamatos/análise , Glutamatos/metabolismo , Ácido Glutâmico , Proteínas do Tecido Nervoso/análise , Ratos , Ratos Endogâmicos , Sinaptossomos/metabolismoRESUMO
Verapamil at 200 microM, prevented the respiratory stimulation, K+ loss, transmitter release, and 45Ca2+ entry into incubated synaptosomes evoked by veratrine (25 to 75 microM) or by high K+ (56 mM). Verapamil (100 microM) also blocked gamma-aminobutyric acid homoexchange, whilst tetrodotoxin was ineffective. Much lower concentrations of verapamil (less than 1 microM) blocked the 45Ca2+ entry caused by veratrine, but not its action in releasing neurotransmitter or K+. It is concluded that verapamil, at 30 to 200 microM, blocks active Na+ channels, thereby preventing depolarization. At greater than 1 microM, verapamil blocks Ca+ channels selectively.