Dominant physical and biological processes in ecosystems occur at specific scales of space and time. The life-spans and the life-spaces (areas used by species over their lifetime) become entrained to operate at similar scales. Because life-spans and life-spaces are related to body size, ecosystems display polymodality in body size distributions: Holling's textural discontinuity hypothesis, TDH. Falsification of the TDH requires either changing the frequencies of the dominant processes or changing the species. Both are difficult to achieve for regional-scale faunas, but the transformation of the terrestrial fauna of New Zealand by humans over the past 800 years provides an opportunity to explore the effect of changing the species. Our analyses of the pre and post first-contact with humans assemblages show that species body size spectra are polymodal and similar (the spectrum is conservative in shape), both pre- and post-spectra exhibiting three distinct modes, despite significant changes in the taxonomic make-up of the fauna. Our findings are consistent with the TDH, but not consistent with other known competing explanations. There is also a compelling case that invasions and introductions have been more successful in the body size range that falls between modes. This is also consistent with the TDH, but not necessarily at odds with explanations based on propagule pressure.