Permutation Tests to Identify Significant Constraint or Promotion Within Biological Scatterplots.

Scatterplots of biological datasets often have no-data zones, which suggest constraint or promotion of dependent variables. Although methods exist to estimate boundary lines-that is, to fit lines to the edges of scatters of data points-there are, to our knowledge, none available to assess the significance of the areal extents of no-data zones. Accordingly, we propose a flexible boundary line definition paired with a permutation test of the magnitude of no-data zones-rather than testing the shape or slope of the line as current methods do.

Soil geochemistry and constraint of tree seedlings immediately after germination on termite mounds in the Kruger National Park, South Africa.

termite mounds in the Kruger National Park occupy a significant part of the savanna landscapes, occurring at densities of up to 70 km and often exceeding 10 m in width and 4 m in height. The mounds are usually devoid of trees, but have dense grass cover in wet years. As a result, these mounds form large patches of grassland amongst the wooded savanna.