Table 4.
Factors determining biotic and abiotic environmental heterogeneity
| Biotic heterogeneity | ||
|---|---|---|
| Higher | Lower | References |
| Complex ecosystems with high degree of competition, predation, and parasitism; e.g. ancient lakes | Simple ecosystems low degree of competition, predation, and parasitism; for example, ephemeral, marginal, extreme habitats | Martens (1998); Martens and Schön (2000); Schön and Martens (2004) versus Bell (1982); Tobler, Schlupp, de Leon, Glaubrecht, and Plath (2007) |
| Unpredictable changes (predator‐prey cycles etc.) | Predictable changes (predator–prey cycles etc.) | Dawkins and Krebs (1979); Tokeshi (1999) |
| Tight and specific association with prey or host; e.g. predatory or parasitic lifestyle | Loose association with prey or host; for example, filtering or micropredatory lifestyle | Dawkins and Krebs (1979) |
| No adaptations to avoid competition, predation, and parasitism; e.g. durable resting stages | Adaptations to avoid competition, predation, and parasitism; for example, durable resting stages | Dawkins and Krebs (1979); Wilson (2011) |
| Planktonic or nektonic lifestyle | Benthic or sedentary lifestyle | Emiliani (1982, 1993a,b); Suttle, Chan, and Cottrell (1990); Bratbak, Egge, and Heldal (1993); Fuhrman (1999); Wommack and Colwell (2000); Fisher, Wieltschnig, Kirschner, and Velimirov (2003); Bettarel, Bouvy, Dumont, and Sime‐Ngando (2006); Filippini, Buesing, Bettarel, Sime‐Ngando, and Gessner (2006); Suttle (2005), Suttle (2007) |
| Not inhabiting soil, or only shallow soil horizons | Inhabitancy of soil, especially deep soil horizons | Wallwork (1970); Elliott, Anderson, Coleman, and Cole (1980); Murphy and Tate (1996); Drake, Choi, Haskell, and Dobbs (1998); Fisher et al. (2003); Lavelle and Spain (2003); Paul (2007) |
| Lower latitudes | Higher latitudes | Rohde (1986); Rohde and Heap (1998); Tokeshi (1999) |
| Shallower parts of water column | Deeper parts of water column | Etter, Rex, Chase, and Quattro (2005) |
| Abiotic heterogeneity | ||
| Temporally changeable (on ecological timescales), spatially very heterogeneous, diverse and unstable habitats with unequally distributed resources; e.g. ephemeral and marginal habitats | Temporally stable, spatially homogeneous habitats with equally distributed resources; for example, caves, ground water reservoirs or soil environment (especially deeper soil horizons or soils of certain biomes) | Wallwork (1970); Farrar (1978); Farrar (1990); Farrar (1998); Krivolutsky and Druk (1986); Siepel (1994),; Siepel (1996); Pejler (1995); Lavelle and Spain (2003); Coleman, Crossley, and Hendrix (2004); Quesada et al. (2004); Paul (2007); Devetter and Scholl (2014) |
| Unpredictable changes | Predictable changes (e.g., cyclical) | Tokeshi (1999) |
| No adaptations to avoid temporary adverse abiotic conditions or enable migration; e.g. durable resting stages | Adaptations to avoid temporary adverse abiotic conditions or enable migration; for example, durable resting stages | Wilson (2011) |
| Extreme yet spatiotemporally changeable habitats; for example, nunataqs, desiccating ponds, bark surface | Temporally stable extreme habitats; e.g. hot springs or subsurface cavities | Bell (1982) |
| Lower latitudes and altitudes | Higher latitudes and altitudes | Hörandl (2006, 2009); Vrijenhoek and Parker (2009) |
| Freshwater habitats and coastal areas | Deeper parts of water column | Etter et al. (2005); Sheldon (1996) |
Summary of factors that were evaluated to determine a higher or a lower environmental heterogeneity of AAs in comparison with their sexual controls. Note that the factors are not universal (a terrestrial organism cannot be benthic/nektonic etc.) and cannot be compared across all studies organisms. See Supporting information Materials and Methods for commentary and detailed description on how we determined biotic and abiotic environmental heterogeneity.