Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, USA.
Program in Ecology and Evolutionary Biology, Department of Biosciences, Rice University, Houston, Texas, USA.
Ecology. 2023 Apr;104(4):e3990. doi: 10.1002/ecy.3990. Epub 2023 Feb 27.
The center-periphery hypothesis predicts a decline in population performance toward the periphery of a species' range, reflecting an alteration of environmental conditions at range periphery. However, the rare demographic tests of this hypothesis failed to disentangle the role of geography from that of ecological niche and are biased toward temperate regions. We hypothesized that, because species are expected to experience optimal abiotic conditions at their climatic niche center, (1) central populations will have better demographic growth, survival, and fertility than peripheral populations. As a result, (2) central populations are expected to have higher growth rates than peripheral populations. Peripheral populations are expected to decline, thus limiting species range expansion beyond these boundaries. Because peripheral populations are expected to be in harsh environmental conditions, (3) population growth rate will be more sensitive to perturbation of survival-growth rather than fertility in peripheral populations. Finally, we hypothesized that (4) soils properties will drive the variations in population growth rates for narrowly distributed species for which small scale ecological factors could outweigh landscape level drivers. To test these hypotheses, we studied the demography of Thunbergia atacorensis (Acanthaceae), a range-limited herb in West Africa. We collected three years of demographic data to parameterize an integral projection model (IPM) and estimated population level demographic statistics. Demographic vital rates and population growth rates did not change significantly with distance from geographic or climatic center, contrary to predictions. However, populations at the center of the geographic range were demographically more resilient to perturbation than those at the periphery. Soil nitrogen was the main driver of population growth rate variation. The relative influence of survival-growth on population growth rates exceeded that of fertility at the geographic range center while we observed the opposite pattern for climatic niche. Our study highlights the importance of local scale processes in shaping the dynamics and distribution of range-limited species. Our findings also suggest that the distinction between geographic distribution and climatic niche is important for a robust demographic test of the center-periphery hypothesis.
中心-边缘假说预测，随着物种分布范围向边缘的推移，种群表现会下降，这反映了环境条件在分布范围边缘的变化。然而，这种假说的罕见人口统计学检验未能将地理因素与生态位区分开来，而且偏向于温带地区。我们假设，由于物种预计在其气候生态位中心经历最佳的非生物条件，（1）中心种群的人口增长、生存和繁殖能力将优于边缘种群。因此，（2）中心种群的增长率预计高于边缘种群。边缘种群预计会下降，从而限制了物种在这些边界之外的扩张。由于边缘种群预计处于恶劣的环境条件下，（3）边缘种群的人口增长率对生存-增长的干扰将比繁殖力更为敏感。最后，我们假设（4）土壤特性将驱动分布范围狭窄的物种的种群增长率变化，因为小尺度的生态因素可能超过景观水平的驱动因素。为了检验这些假设，我们研究了西非范围有限的草本植物 Thunbergia atacorensis（爵床科）的人口统计学。我们收集了三年的人口统计学数据，以参数化积分投影模型（IPM）并估计人口统计学的统计数据。人口统计学的重要生活史特征和种群增长率并没有随着与地理或气候中心的距离而显著变化，这与预测结果相反。然而，与地理范围边缘的种群相比，地理范围中心的种群在人口统计学上对干扰更具弹性。土壤氮是种群增长率变化的主要驱动因素。在地理范围中心，生存-增长对种群增长率的相对影响大于繁殖力，而在气候生态位中则观察到相反的模式。我们的研究强调了本地尺度过程在塑造有限分布物种的动态和分布方面的重要性。我们的研究结果还表明，在对中心-边缘假说进行稳健的人口统计学检验时，地理分布和气候生态位之间的区别很重要。
