The dynamics of vegetation grazed by a food-limited population of Soay sheep on St Kilda
The dynamics of vegetation grazed by a food-limited population of Soay sheep on St Kilda
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DOI：
10.1111/1365-2745.13782
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发表时间：
2021-11-02
影响因子：
5.5
通讯作者：
Pemberton, Josephine M.
中科院分区：
文献类型：
--
作者：
Crawley, Michael J.;Pakeman, Robin J.;Pemberton, Josephine M.
35年来，外赫布里底群岛希尔塔岛上的Soay绵羊种群一直是持续研究的对象。本文侧重于植物-食草动物相互作用的植物学方面，展示了植被如何影响绵羊以及如何受到绵羊的影响。放牧对不同植物群落生物量和空间结构的影响是不同的，其中Holcus/Agrostis草原受影响最大，Wet Heath受影响最小，这与草食动物影响与植物生产力成正比的假设相一致。在植物群落内部，绵羊数量与植物丰富度(草皮高度、林隙/草丛盖度和生物量)之间的负相关在3月份显著，但在8月份不显著，如果冬季的食物供应限制了绵羊数量的话。在大多数物种中，花茎密度随着绵羊数量的增加而下降。没有令人不快的植物表现出开花增加的例子(例如，在选择性放牧下竞争对手的释放)。由于历史养分供应和小气候的差异，临时封禁(地上净初级生产力)的植物生产量以Holcus/Agrostis草原最大(12.6 t ha(-1)年)，Nardus草原较低(5.1 t ha(-1)年)，车前草(1.3 t ha(-1)年(-1))。放牧对植物物种丰富度的净影响是积极的：少数适口性强的物种被排除在外，但落叶促进了耐牧性物种的小规模共存。Soay绵羊的数量从1988年的908只波动到2009年的2208只，在1985-2011年间平均每年增加39只。在2011至2020年间，人口波动幅度较小，没有显示出任何趋势。种群变化(ln(N(t+1)/N(T)与密度成反比，但与草地植物产量呈正相关，在研究过程中植物产量有所增加。这种植物-食草动物的相互作用具有很强的弹性，尽管在Holcus/Agrostis草原上，一些物种(红羊茅和毛茅)数量下降，但不适口的植物物种的丰度没有显著上升的趋势。综合。对植物-食草动物数据的未来研究和分析的影响。专注于估计初级生产力和食草动物的收获，而不是简单地测量植物生物量的变化，可能会为理解食草动物的种群动态提供极大的解释能力。
The population of Soay sheep on the island of Hirta in the Outer Hebrides has been the subject of continuous study for more than 35 years. This paper focuses on the botanical aspects of the plant-herbivore interaction, showing how the vegetation affects and is affected by the sheep. Grazing impacts on biomass and spatial structure varied across plant communities, with Holcus/Agrostis grasslands affected most and Wet Heath least, consistent with the hypothesis that herbivore impacts are proportional to plant productivity. Within plant communities, the negative relationships between sheep numbers and plant abundance (sward height, gap/tussock cover and biomass) were significant in March but not significant in August, as expected if sheep numbers are limited by food supply in winter. In most species, flower stem density declined with increasing sheep numbers. There were no examples where unpalatable plants showed increased flowering (e.g. from competitor release under selective grazing). Plant production in temporary grazing exclosures (above-ground net primary production) was greatest in Holcus/Agrostis grassland (12.6 t ha(-1) dry matter year(-1)), lower in Nardus grassland (5.1 t ha(-1) year(-1)) and least in Plantago sward (1.3 t ha(-1) year(-1)) associated with differences in historical nutrient supply and microclimate. The net effect of grazing on plant species richness was positive: A few highly palatable species were excluded, but small-scale coexistence of grazing-tolerant species was enhanced by defoliation. The Soay sheep population fluctuated from 908 (in 1988) to 2,208 (in 2009), increasing by an average of 39 extra animals per year over the period 1985-2011. Between 2011 and 2020, the population fluctuated less widely and showed no trend. Population change (ln(N(t + 1)/N(t))) was inversely density dependent but positively correlated with plant production in Holcus/Agrostis grassland which increased during the study. This plant-herbivore interaction is highly resilient, and though some species (Festuca rubra and Ranunculus acris) declined in the Holcus/Agrostis grassland, there was no significant upward trend in the abundance of unpalatable plant species. Synthesis. Implications for future studies and analyses of plant-herbivore data. Concentrating on estimating primary productivity and herbivore offtake, rather than simply measuring change in plant biomass, is likely to provide greatly improved explanatory power for understanding herbivore population dynamics.