Trends in Food Crop Yields under Demographic Pressure in Sub-Saharan Africa: the Case of Cassava in Southeast Nigeria

1995 ◽  
Vol 24 (4) ◽  
pp. 249-254 ◽  
Author(s):  
Anselm A. Enete ◽  
Felix I. Nweke ◽  
Eugene C. Okorji
Keyword(s):  
Population Density ◽  
Large Population ◽  
Sub Saharan Africa ◽  
High Population ◽  
High Population Density ◽  
Root Yield ◽  
National Team ◽  
Cassava Root ◽  
Density Area ◽  
Cassava Plant

Research in 1973 attributed large cassava root yield differences among three villages in southeast Nigeria to equally large population density differences. In 1993, the Nigerian national team of the Collaborative Study of Cassava in Africa (COSCA) went back to the three villages to see whether population growth had led to yield declines. They found that the wide gap in yields between the high and low population density villages was maintained, apparently due to differences in soil type, fallow periods, cassava plant densities and harvest dates. Cassava root yield had doubled in the high population density area, increased but not doubled in the medium population density area and declined in the low population density area. The differences in the yield trends among the three villages were due to the use of improved cassava varieties in the high population density area.

Conservation in areas of high population density in sub-Saharan Africa

2007 ◽  
Vol 134 (2) ◽  
pp. 155-163 ◽  
Author(s):  
Norbert J. Cordeiro ◽  
Neil D. Burgess ◽  
Delali B.K. Dovie ◽  
Beth A. Kaplin ◽  
Andrew J. Plumptre ◽  
...  
Keyword(s):  
Population Density ◽  
Sub Saharan Africa ◽  
High Population ◽  
High Population Density ◽  
Sub Saharan

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

Aggregations of masked shrews ( Sorex cinereus ): density-related mating behavior? / Agrégation de musaraignes masquées ( Sorex cinereus ): accouplement relatif à la densité de la population?

Mammalia ◽  
2006 ◽  
Vol 70 (1-2) ◽  
Author(s):  
Thomas J. Maier ◽  
Katherine L. Doyle
Keyword(s):  
Population Density ◽  
Mating Behavior ◽  
High Population ◽  
High Population Density ◽  
Genetic Analyses ◽  
Highly Active ◽  
Sorex Cinereus

AbstractLarge aggregations of shrews have been reported and various explanations offered for this seemingly rare behavior; however, there has been little evidence to support any particular interpretation. We observed two small aggregations of highly active vocalizing Sorex cinereus while performing wildlife surveys in forested habitats in central Massachusetts, USA. These observations, in conjunction with a review of other reports, including genetic analyses, strongly suggest that such aggregations of adult Sorex are associated with mating behavior, more readily observed during periods of high population density. Published accounts of such behavior may be rare because primarily large aggregations have been reported; however, smaller breeding aggregations may be common.

Analysis of steroid hormone levels in female mice at high population density

1998 ◽  
Vol 64 (4) ◽  
pp. 529-533 ◽  
Author(s):  
John C Chapman ◽  
John J Christian ◽  
Mary Ann Pawlikowski ◽  
Sandra D Michael
Keyword(s):  
Population Density ◽  
Steroid Hormone ◽  
High Population ◽  
High Population Density ◽  
Hormone Levels ◽  
Female Mice
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