0 5 10 15 20 25 30 35 40 45 50 52 53 55 60 65 70 75 80 85 90 95 100 105 1 The birds and the seas: body size reconciles differences in the abundance-occupancy relationship across marine and terrestrial vertebrates Thomas J. Webb, Nicholas K. Dulvy, Simon Jennings and Nicholas V.C. Polunin T. J. Webb (t.j.webb@sheffield.ac.uk), Dept of Animal and Plant Sciences, Univ. of Sheffield, Sheffield, S10 2TN, UK. – N. K. Dulvy, Biological Sciences, Simon Fraser Univ., Burnaby, BC, V5A 1S6, Canada. – S. Jennings, Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, NR33 0HT, UK and School of Environmental Sciences, Univ. of East Anglia, Norwich, NR4 7TJ, UK. – N. V. C. Polunin, School of Marine Science and Technology, Newcastle Univ., NE1 7RU, UK. Despite some fundamental differences in production processes and the ecology of consumer species on land and in the sea, further understanding of pattern and process in both biomes might be gained by applying common methods of mac- roecological analysis. We develop methods that reconcile apparent differences in abundance and occupancy for marine and terrestrial vertebrates, as exemplified by fish and birds. hese recognize and take account of those aspects of the life history and ecology of marine and terrestrial animals that influence their abundance, distribution and trophic role. When abundance and occupancy are averaged within species over time we show that variation within a region is less for birds than fish, but when abundance and occupancy are averaged over space, the difference between birds and fish disappears. Further, we develop size rather than species-structured abundance-occupancy relationships for fish assemblages and demonstrate that patterns of intra-size class variation that are very similar to intraspecific variation in bird species, over both time and space. We argue that this result reflects the relative importance of body size and species identity respectively in determining trophic roles in marine and terrestrial environments. Selection of the appropriate analytical unit on land (species) and in the sea (size) helps to reconcile apparently divergent macroecological patterns, especially when these are driven by contrasting patterns of energy acquisition and use. ‘I argue that we should attempt to address the question of [ecological] generalizations capable of crossing the land-to-sea boundary’ (Steele 1991a, p. 425). ‘…a strong conceptual framework for comparing life in the marine realm with life on land has not been developed’ (Dawson and Hamner 2008, p. 137). he exchange of ideas between marine and terrestrial ecol- ogy has largely been limited to a few targeted efforts (Steele 1991a, Beddington et al. 1994, Stergiou and Browman 2005). his reflects the ‘wet’ and ‘dry’ division of many facil- ities, journals, meetings and funding streams (Raffaelli et al. 2005, Menge et al. 2009, Webb 2009), a possible response by scientists to the physical and biological differences between systems. Although biophysical differences between marine and terrestrial systems can be overstated (Dawson and Hamner 2008), in terms of primary production and the ecology of consumer species these systems do differ fundamentally. he dominant primary producers in the sea are unicellular, motile, short lived and very responsive to short term changes in the physical environment while the dominant primary producers on land often provide structure, can grow in mass by many orders of magnitude and are often relatively unresponsive to short term environmental fluctuations. Further, major groups of marine consumers (especially fish) tend to grow over many orders of magnitude in mass, change habitats and prey types with size, release large numbers of small pelagic eggs and provide no parental care while ter- restrial vertebrate consumers have limited scope for growth, form long-term associations with habitat and provide their larger young with significant parental care. One consequence of the differences between marine and terrestrial systems is that size rather than species identity accounts for most of the variation in the trophic roles of marine animals. Recognition of the significance of size led to the emergence of theory and applications that describe marine food web and system properties in terms of size composition (Kerr and Dickie 2001). Conversely, terrestrial food web theory focuses on species and on groups of spe- cies with similar trophic roles. he marine approach reflects the dominance of small primary producers in the marine environment, the relatively consistent relationships between predator and prey body sizes and the considerable scope for growth in many marine species, often exceeding five orders of magnitude in mass (Cushing 1975). Since many mac- roecological patterns and processes are a consequence of the energy demands and life histories of the species in a community (Brown et al. 2004) the development of theory Oikos 000: 001–013, 2011 doi: 10.1111/j.1600-0706.2011.18870.x © 2011 he Authors. Oikos © 2011 Nordic Society Oikos Subject Editor: Andrea Belgrano. Accepted 18 November 2010 OIKO_A_018870.indd 1 OIKO_A_018870.indd 1 1/6/2011 5:22:08 PM 1/6/2011 5:22:08 PM