Mammalian intestinal allometry, phylogeny, trophic level and climate

An often-stated ecomorphological assumption that has the status of
‘textbook knowledge’ is that the dimensions of the digestive tract
correlate with diet, where herbivores – consuming diets of lower
digestibility – have longer intestinal tracts than faunivores – consuming
diets of higher digestibility. However, statistical approaches have so far
failed to demonstrate this link. Here, we collated data on the length of
intestinal sections and body mass of 519 mammal species, and test for
various relationships with trophic, climatic and other biological
characteristics. All models showed a strong phylogenetic signal. Scaling
relationships with body mass showed positive allometry at exponents
>0.33, except for the caecum, which is particularly large in
smaller species. Body mass was more tightly linked to small intestine than
to large intestine length. Adding a diet proxy to the relationships
increased model fit for all intestinal sections, except for the small
intestine when accounting for phylogeny. Thus, diet has a main effect on
the components of the large intestine, with longer measures in herbivores.
Additionally, measures of habitat aridity had a positive relationship with
large intestine length. The small intestine was longer in species from
colder habitats at higher latitudes, possibly facilitating the processing
of peak intake rates during the growing season. This study corroborates
intuitive expectations on digestive tract anatomy, while the dependence of
significant results on large sample sizes and inclusion of specific
taxonomic groups indicates that the relationships cannot be considered
fixed biological laws.

生态形态学中一个常被提及且具有“教科书知识”地位的假设是，消化道的尺寸与饮食相关：植食性动物（摄食消化率较低的食物）的肠道比食动物者（摄食消化率较高的食物）更长。然而，迄今为止的统计方法未能证明这种关联。在此，我们整理了519种哺乳动物的肠道各段长度和体重数据，并测试了其与营养、气候及其他生物学特征的多种关系。所有模型均显示出强烈的系统发育信号。与体重的尺度关系呈现正异速生长，指数大于0.33，但盲肠除外——盲肠在较小物种中尤为发达。体重与小肠长度的关联比与大肠长度的关联更紧密。在关系中加入饮食替代指标后，所有肠道段的模型拟合度均有所提高，但考虑系统发育时小肠除外。因此，饮食对大肠各部分有主要影响，植食性动物的大肠更长。此外，栖息地干旱度与大肠长度呈正相关。高纬度寒冷栖息地的物种小肠更长，这可能有助于在生长季节处理峰值摄食率。本研究证实了对消化道解剖结构的直觉预期，但显著结果依赖于大样本量和特定分类群的纳入，这表明这些关系不能被视为固定的生物学规律。