Department of Wildlife Ecology and Conservation, Fort Lauderdale Research and Education Center, University of Florida, Davie, Florida, United States of America.
South Florida Natural Resources Center, National Park Service, Homestead, Florida, United States of America.
PLoS One. 2023 Feb 24;18(2):e0282093. doi: 10.1371/journal.pone.0282093. eCollection 2023.
Body condition is a measure of the health and fitness of an organism represented by available energy stores, typically fat. Direct measurements of fat are difficult to obtain non-invasively, thus body condition is usually estimated by calculating body condition indices (BCIs) using mass and length. The utility of BCIs is contingent on the relationship of BCIs and fat, thereby validation studies should be performed to select the best performing BCI before application in ecological investigations. We evaluated 11 BCIs in 883 Argentine black and white tegus (Salvator merianae) removed from their non-native range in South Florida, United States. Because the length-mass relationship in tegus is allometric, a segmented linear regression model was fit to the relationship between mass and length to define size classes. We evaluated percent, residual, and scaled fat and determined percent fat was the best measure of fat, because it was the least-associated with snout-vent length (SVL). We evaluated performance of BCIs with the full dataset and within size classes and identified Fulton's K as the best performing BCI for our sampled population, explaining up to 19% of the variation in fat content. Overall, we found that BCIs: 1) maintained relatively weak relationships with measures of fat and 2) splitting data into size classes reduced the strength of the relationship (i.e., bias) between percent fat and SVL but did not improve the performance of BCIs. We postulate that the weak performance of BCIs in our dataset was likely due to the weak association of fat with SVL, the body plan and life-history traits of tegus, and potentially inadequate accounting of available energy resources. We caution against assuming that BCIs are strong indicators of body condition across species and suggest that validation studies be implemented, or that alternative or complimentary measures of health or fitness should be considered.
体况是生物体健康和体能的一种衡量标准，通常用可用的能量储备（即脂肪）来表示。直接测量脂肪是很难做到非侵入性的，因此体况通常是通过使用质量和长度计算体况指数（BCI）来估计的。BCI 的实用性取决于 BCI 与脂肪的关系，因此在应用于生态调查之前，应该进行验证研究来选择表现最佳的 BCI。我们评估了 883 只从美国佛罗里达州非原生范围中捕获的阿根廷黑白刺尾鬣蜥（Salvator merianae）的 11 个体况指数。由于刺尾鬣蜥的体长与质量关系是异速生长的，因此我们使用分段线性回归模型来拟合质量与长度之间的关系，以定义体型类别。我们评估了脂肪的百分比、残差和比例，并确定脂肪百分比是衡量脂肪的最佳指标，因为它与吻肛长（SVL）的关联最小。我们使用完整数据集和体型类别评估了 BCI 的性能，并确定富尔顿 K 是我们采样种群中表现最佳的 BCI，可解释高达 19%的脂肪含量变化。总的来说，我们发现 BCI：1）与脂肪测量值保持相对较弱的关系；2）将数据分为体型类别会降低脂肪百分比和 SVL 之间的关系强度（即偏差），但不能提高 BCI 的性能。我们假设 BCI 在我们的数据集表现不佳可能是由于脂肪与 SVL 的弱关联、刺尾鬣蜥的身体结构和生活史特征，以及可能无法充分考虑可用的能量资源。我们告诫不要假设 BCI 是跨物种体况的强有力指标，并建议实施验证研究，或考虑使用其他或补充的健康或体能衡量指标。
