Nearshore–offshore–basin species diversity and body size variation patterns in Late Permian (Changhsingian) brachiopods
Nearshore–offshore–basin species diversity and body size variation patterns in Late Permian (Changhsingian) brachiopods
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DOI：
10.1016/j.palaeo.2015.07.046
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发表时间：
2016-04
期刊：
影响因子：
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通讯作者：
G. Shi;Yi‐chun Zhang;S. Shen;Weihong He
中科院分区：
文献类型：
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作者：
G. Shi;Yi‐chun Zhang;S. Shen;Weihong He
体型是有机体的基本和决定性特征，其在空间和时间上的变化通常被认为是其生物学以及与其生活环境相互作用的函数。已经进行了大量与体型相关的生态和进化研究，主要是与现存动物有关。在提出和测试的许多与身体尺寸相关的假设中，尺寸与水深测量的关系可能是研究最少的。在本研究中，我们编制了低纬度地区（30°S–30°N）长兴纪（晚二叠世，约 254 Ma–252 Ma）腕足类物种的全球体型数据集，并分析了它们的物种多样性和体型分布模式与近岸-近海-盆地测深梯度的关系。该数据集包含来自18个不同古地理区域的135个地点（地点）的9目159属435种的1768个腕足动物标本。将整个长兴阶视为一个时间片，我们将近岸-近海-盆地测深梯度分为三个与深度相关的环境：近岸、近海和盆地环境，并比较了物种多样性和体型大小沿着这个大范围测深梯度的变化。在这里，我们报告了一系列复杂的模式。首先，我们发现沿着近岸-近海-盆地梯度，物种多样性与水深之间存在明显的总体负相关，大多数物种集中在近岸环境中。其次，当比较这三种环境中所有低纬度腕足动物物种的中位尺寸时，我们发现近岸和近海环境之间没有显着的尺寸差异，这表明波底和静水压力对腕足动物的体型没有产生关键影响。另一方面，发现近岸环境以及较小程度上近海环境的腕足动物的中位尺寸显着大于盆地腕足动物。盆地腕足动物体型显着减小的趋势反映了盆地环境中物种多样性相对较低，并且这两种情况都不能简单地用深海环境中食物供应量减少的趋势来解释。相反，这两种趋势都与深海（斜坡到深海）环境中不断扩大的最低氧气区（OMZ）的假设相一致，其中缺氧到缺氧的条件被认为严重限制了底栖动物的多样化，并有利于小型腕足动物的相对增殖。最后，在广深水物种和窄深水物种之间，其体型大小对近岸-近海-盆地梯度的响应也存在显着差异，因为广深水物种（在所有三种环境中发现的物种）不会根据深度而显着改变其体型大小，而窄深物种（仅限于单一环境的物种）在朝向盆地环境时表现出体型下降。这种模式被解释为表明，在测深方面更耐受的物种在其体型变化动态方面对深度控制不太敏感，相比之下，在较浅的水深中往往会长得更大的窄水物种。
Body size is a fundamental and defining character of an organism, and its variation in space and time is generally considered to be a function of its biology and interactions with its living environment. A great deal of body size related ecological and evolutionary research has been undertaken, mostly in relation to extant animals. Among the many body size-related hypotheses proposed and tested, thesize–bathymetryrelationship is probably the least studied. In this study, we compiled a global body size dataset of Changhsingian (Late Permian, ca. 254 Ma–252 Ma) brachiopod species from low-latitude areas (30°S–30°N) and analyzed their species diversity and body size distribution patterns in relation to the nearshore–offshore–basin bathymetric gradient. The dataset contained 1768 brachiopod specimens in 435 species referred to 159 genera and 9 orders, from 135 occurrences (localities) of 18 different palaeogeographic regions. Treating the whole of the Changhsingian Stage as a single time slice, we divided the nearshore–offshore–basin bathymetric gradient into three broad depth-related environments: nearshore, offshore and basinal environments, and compared how the species diversity and body size varied along this large-scale bathymetric gradient.Here, we report an array of complex patterns. First, we found a clear overall inverse correlation between species diversity and water depth along the nearshore–offshore–basin gradient, with most species concentrating in the nearshore environment. Second, when the median sizes of all low-latitude brachiopod species from the three environments were compared, we found that there was no significant size difference between the nearshore and offshore environments, suggesting that neither the wave base nor the hydrostatic pressure exerts a critical influence on the body size of brachiopods. On the other hand, the median sizes of brachiopods from the nearshore environment and, to a lesser extent, the offshore environment were found to be significantly larger than that of basinal brachiopods. This trend of significant size reduction in basinal brachiopods mirrors the relative low species diversity in the basinal environment, and neither can be easily explained by the tendency of decreasing food availability towards deeper sea environments. Rather, both trends are consistent with the hypothesis of an expanding Oxygen Minimum Zone (OMZ) in the bathyal (slope to deepsea) environments, where hypoxic to anoxic conditions are considered to have severely restricted the diversification of benthos and favored the relative proliferation of small-sized brachiopods. Finally, a significant difference was also found between eurybathic and stenobathic species in their body size response to the nearshore–offshore–basin gradient, in that eurybathic species (species found in all three environments) did not tend to change their body size significantly according to depth, whereas stenobathic forms (species restricted to a single environment) exhibit a decline in body size towards the basinal environment. This pattern is interpreted to suggest that bathymetrically more tolerant species are less sensitive to depth control with respect to their body size change dynamics, in contrast to stenobathic species which tend to grow larger in shallower water depths.