596


CAITLIN R. KEATING-BITONTI AND JONATHAN L. PAYNE


on an intermediate, and potentially optimal, body size with increasing water depth, leading to the hypothesis that evolutionary dynamics in the deep sea behave similarly to those of island systems (McClain et al. 2006). The island rule describes a convergence of large and small terrestrial organisms toward an intermediate and potentially physiological or develop- mentally optimal size as a function of resource limitation and release from predation pressures on islands relative to their mainland counter- parts (Foster 1964; Van Valen 1973). Similar to the island biogeographic size hypothesis, extant terebratulid brachiopods decrease in size with increasing water depth, possibly reflecting resource limitation (Peck and Harper 2010). There also exist exceptions to these biogeographic rules, such as the invariance of bivalve size distributions across latitude in the eastern Pacific(Royetal. 2000). Despite the similarities in patterns, many


examples of biogeographic variation in morphology in the marine realm result from different proximal environmental controls than those in terrestrial systems (Forster et al. 2012). For example, abalone size is inversely associated with water temperature, but this pattern has been attributed to higher rates of primary production in cold waters (Estes et al. 2005). Similarly, the mean biomass of the marine invertebrate fauna decreases with water depth as a function of decreased supply of organic carbon to the deep sea (Rex et al. 2006). After controlling for water depth, the maximum size of deep-sea turrid gastropods increases as a function of increasing levels of dissolved oxygen (McClain and Rex 2001). These different environmental explanations for size variation in the oceans highlight the complex nature of this environment. Rather than one single oceanographic factor


being responsible for shaping these spatial size trends, multiple factors might underlie them. A particular challenge for studies attempting to identify the controls on organismal morphol- ogy in the oceans is the covariation among environmental parameters, such as between temperature, dissolved oxygen concentration, and particulate organic carbon flux (Levin and Gage 1998). Each of these oceanographic parameters influences metabolism, and thus


for investigating the influences of a number of oceanographic parameters on organism size and volume–to–surface area ratio. They are a diverse and abundant group of rhizarian protists possessing reticulose pseudopods and inhabiting nearly all marine environments. Most species produce mineralized shells (tests) that facilitate the analysis of cell morphology in both living and dead individuals. Moreover, within local environmental settings they vary in test morphology with fluctuations in particulate organic carbon flux (Corliss and Chen 1988; Jorissen et al. 1995) and oxygen concentration (Bernhard 1986; Kaiho 1999a,b; Payne et al. 2012a), but controls on continental-scale variation in size and volume–to–surface area ratio have yet to be assessed. In this study we evaluate the correspondence between modern benthic Rotallid foraminiferal test size and volume–to–surface area ratio from the North American continental margin and the oceano- graphic variables most frequently hypothesized to influence organismmetabolism.


each can also potentially constrain size and volume–to–surface area ratio (Gillooly et al. 2001). For example, a study of modern marine amphipod crustaceans attributes the positive correlation between body size and latitude to increased levels of dissolved oxygen in colder waters at higher latitudes (Chapelle and Peck 1999). Alternatively, decreased food availability and increased costs of foraging in the cold, deep sea has been hypothesized to place constraints on the maximum size of marine mollusks (Rex and Etter 1998; McClain et al. 2012a). However, we are aware of no previous study that has analyzed spatial gradients in size while simultaneously assessing multiple environmental influences on physiology. Benthic foraminifera are an ideal study group


Methods To determine the primary environmental


controls on the size and volume–to–surface area ratio of benthic foraminifera across broad geographic scales, we combined data on test dimensions for 541 species of Rotallid foraminifera with occurrence data that span across 60 degrees of latitude and 1600m of water depth around the North American


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192