Key Factors in Population Studies

Varley, G. C.; Gradwell, G. R.

doi:10.2307/2213

Cited by 505 publications

(221 citation statements)

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“…Foi considerado como componente crítico de perdas aquele cuja correlação foi significativa pelo teste t a p<0,05 (Varley & Gradwell, 1960). Entretanto, se mais de uma dessas correlações foi significativa, foram realizadas análises de regressão linear entre essas perdas parciais em função das perdas totais, sendo considerado como componente crítico de perdas aquele cuja equação de regressão apresentou o maior coeficiente angular a p<0,05 (Podoler & Rogers, 1975).…”

Section: Methodsunclassified

Intensidades de perdas, ataque de insetos-praga e incidência de inimigos naturais em cultivares de milho em cultivo de safrinha

Picanço¹,

Galvan²,

Galvão³

et al. 2003

Ciênc. agrotec.

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Conduziu-se este trabalho visando a estudar as intensidades de perdas, densidades de insetos-praga e inimigos naturais em 49 cultivares de milho (Zea mays L.) em cultivo de safrinha em Coimbra, MG, Brasil. A produtividade média das cultivares foi de 3438,74 kg/ha, sendo as cultivares Traktor, CDX98D06, CO9621, OC705 e 97TR61 as mais produtivas. Ocorreram 29,62% de perdas na produtividade das cultivares, devido principalmente ao ataque de Sitophilus zeamais (Motsch., 1865) (Coleoptera: Curculionidae) aos grãos. O inseto-praga mais abundante foi Dalbulus maidis (DeLong & Wolcott, 1923) (Homoptera: Cicadellidae), seguido por adultos de Diabrotica speciosa (Germ., 1824) (Coleoptera: Chrysomelidae) e lagartas de Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae). O inimigo natural mais abundante foi o predador Doru luteipes (Scudder, 1876) (Dermaptera: Forficulidae). As densidades desses insetos foram semelhantes nas cultivares, com exceção de D. maidis. As cultivares menos atacadas por D. maidis foram: SHS5060, COE9994, HT8A97, NB6077, Z8550, CD3351, Maister, AG122, HS12L1133, HT47C, 97TR61, CDX98D04 e A975.

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Section: Methodsunclassified

Intensidades de perdas, ataque de insetos-praga e incidência de inimigos naturais em cultivares de milho em cultivo de safrinha

Picanço¹,

Galvan²,

Galvão³

et al. 2003

Ciênc. agrotec.

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“…Therefore, adaptive clutch size reduction in high-density years leads to reduced competition in later stages. Key-factor analysis used to determine the strength of density-dependent effects during different periods during the life cycle (Varley and Gradwell 1960) will in such a case overestimate the strength of density-dependent processes during the egg-laying stage, and underestimate the effect during the nestling stage. Thus by adjusting reproductive decisions to future levels of competition, birds make it more difficult for us to measure the real extent of density-dependent processes.…”

Section: Adaptation and Population Dynamicsmentioning

confidence: 99%

Adaptive Density Dependence of Avian Clutch Size

Both¹,

Tinbergen²,

Visser³

2000

Ecology

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Abstract. In birds, the annual mean clutch size is often negatively correlated with population density. This relationship is at least in part due to adjustment by individuals. We investigated whether this response is adaptive in two ways. First we used an optimality model to predict how optimal clutch size (the clutch size that maximizes the number of breeding birds [recruits and surviving parents] in the next season) varies with density. We parameterized the model using data on fitness consequences of experimental variation in brood size and natural variation in population density in a Great Tit (Parus major) population. Predicted optimal clutch size decreased with density, but the predicted relationship was stronger than the observed relationship. Second, we investigated the relationship between the annual selection differential for clutch size and density. We found no relationship, indicating that there is no selection for a steeper than observed relationship between clutch size and density. This implies that the observed response is adaptive, and that the prediction of the optimality model lacks some important constraints or selection pressures. We further used the optimality model to examine the sensitivity of the optimal clutch size to density at different stages in the reproductive cycle. This analysis suggested that the nestling stage was most important. To the best of our knowledge this is the first study that makes quantitative predictions of optimal clutch size in relation to population density.

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“…K-, k i -, and k ij -values were calculated as follows (Varley and Gradwell 1960): K = log (no. of produced acorns on trees) À log (no.…”

Section: Discussionmentioning

confidence: 99%

Determinant factors in the seedling establishment of Pasania edulis (Makino) Makino

Nakamura

Hirata

Oishi

et al. 2013

Ecological Research

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Pasania edulis (Makino) Makino is one of the dominant Fagucea tree species in evergreen broad‐leaved forests in southern Japan, and its regeneration success may have a major impact on the dynamics of evergreen broad‐leaved forests. We conducted a field survey on the population process from acorn production to seedling establishment of P. edulis in an evergreen broad‐leaved forest in Kagoshima, southern Japan, from 1995 to 2009. The acorn crop varied greatly among the 14 cohorts, with mast cropping being recorded every 3–4 years. The mortality rate of acorns was very high for all 14 cohorts (99.3–100 %). Important mortality factors were failure to mature (empty acorns), attack by Curculio weevil on trees, predation of dropped acorns by Apodemus mice and large or medium‐sized mammals (wild boar (Sus scrofa leucomystax), badger (Meles meles anakuma), and raccoon dog (Nyctereutes procyonoides viverrinu)), and attacks on germinated acorns by the acorn borer (Coccotrypes graniceps). Among these factors, predation by Apodemus mice was the greatest contributor to annual fluctuations in total mortality until seedling establishment. Large or medium‐sized mammals and the acorn borer also caused severe damage to dropped acorns in some years, but contributed little to annual fluctuations in total mortality. For successful regeneration, mast cropping was essential. However, a small population of Apodemus mice, that is, a low predation pressure, was also required during mast years.

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Key Factors in Population Studies

Cited by 505 publications

References 1 publication

Intensidades de perdas, ataque de insetos-praga e incidência de inimigos naturais em cultivares de milho em cultivo de safrinha

Intensidades de perdas, ataque de insetos-praga e incidência de inimigos naturais em cultivares de milho em cultivo de safrinha

Adaptive Density Dependence of Avian Clutch Size

Determinant factors in the seedling establishment of Pasania edulis (Makino) Makino

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