Density-dependent population dynamics in larvae of the dragonfly Pachydiplax longipennis: a field experiment

Population dynamics of the species Plantago major L. and Poa annua L., typical representatives of ruderal vegetation, was analyzed in a replacement series experiment. The analyzed species were sown in an area with meadow vegetation, where the vegetation present had been previously removed by a total herbicide and additionally by hoeing. The objective of the experiment was to monitor growth dynamics and the effect of intra- and inter-specific interaction of the species Plantago major and Poa annua in conditions of different sowing densities and proportions. The effects of intra- and inter-specific interference and the density-dependent responses were assessed on the basis of several parameters (natality, mortality, age structure, and measures of ontogenetic changes). Based on the study results, it can be concluded that the responses of the species in the experiment were different, which is explained by different adaptive mechanisms, i.e., strategies, in the specific environmental conditions. An effect of the density dependent response was present in both species in the replacement series experiment. The response was amplified by water deficit caused by intensive evapora?tion of the bare soil. No effect of inter-specific interference was observed at the given densities of the study species on the sample plots. An effect of intra-specific interference of the species Plantago major and Poa annua was observed in the guise of a density-negative response of the rate of ontogenetic changes and fecundity.

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Population dynamics in echinococcosis and cysticercosis: regulation ofTaenia hydatigenaandT. ovisin lambs through passively transferred immunity

Parasitology ◽

10.1017/s0031182000079853 ◽

1990 ◽

Vol 101 (1) ◽

pp. 145-151 ◽

Cited By ~ 8

Author(s):

M. A. Gemmell ◽

J. R. Lawson ◽

M. G. Roberts ◽

J. F. T. Griffin

Keyword(s):

Population Dynamics ◽

Natural Environment ◽

Population Regulation ◽

Acquired Immunity ◽

Taenia Hydatigena ◽

Density Dependent ◽

Active Immunity ◽

Infection Pressure ◽

High Infection

SUMMARYA comparison has been made of the interactions between passively transferred and actively acquired immunity in regulating populations ofTaenia hydatigenaandT. ovis.When ewes were grazed prior to parturition under a high infection pressure, immunity was transferred to their offspring for up to 8 weeks. A qualititative difference between the species was the destruction of larvalT. ovisprior to their establishment (‘pre-encystment immunity’) and that ofT. hydatigenaafter they had become established (‘post-encystment immunity’) in the challenged lambs. The major difference in terms of population regulation between the two parasites was that infection occurred withT. hydatigenabut not withT. ovisin those lambs reared from birth for 16 weeks under high infection pressure. Passive, like active immunity, is a density-dependent constraint. It plays an important role in the population regulation ofT. ovis, but not ofT. hydatigena. This is discussed in terms of transmission in the natural environment, an hypothesis on humoral protection and the need to elucidate pathways of protection when immunization schedules are being evaluated for controlling the taeniid zoonoses.

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