Data from: Ant abundance in pitfall traps across different fire treatments

Fire is a dominant ecological force shaping many faunal communities globally. Fire affects faunaeither directly, such as by killing individuals, or indirectly, such as by modifying vegetation structure. Vegetation structure itself also modulates fire frequency and intensity. As such, faunal responses to fire need to be seen through the lens of variable fire activity and vegetation structure. Here, we incorporate information on fire activity and vegetation structure to enhance an understanding of the response of ants to long-term (17-year) experimental fire treatments in an extremely fire-prone tropical savanna in northern Australia. A previous analysis revealed limited divergence in ant communities after five years of experimental fire treatment. Hence, we first investigated the extent to which ant communities diverged over a subsequent 12 years of treatment. We then assessed the relative contribution of fire treatment, cumulative fire intensity(fire activity) and woody cover to responses of ant species frequency of occurrence, richness and composition. We found that, even after 17 years, fire treatments explained little variation in any ant response variable. In contrast, woody cover was a strong predictor for all of them, while fire activity was a moderate predictor for abundance and richness. Ant species occurrence and richness increased in open habitats receiving higher levels of fire activity, compared with plots with higher vegetation cover experiencing low (or no) fire activity. Moreover, species composition differed between plots with high and low vegetation cover. Our findings provide experimental support to the principle that the effects of fire on fauna are primarily indirect, via its effect on vegetation structure. Furthermore, our results show that a 'uniform' fire regime does not have uniform impacts on the ant fauna, because of variability imposed by interactions between vegetation structure and fire activity. This helps explain why there is often a weak relationship between pyrodiversity and biodiversity, and it lessens the need for active management of pyrodiversity to maintain biodiversity.

火是塑造全球众多动物群落的主导性生态作用力。火对动物的影响可分为直接途径与间接途径：直接途径如直接杀死个体，间接途径如改变植被结构。而植被结构本身亦会调控火的发生频率与强度。因此，对火的动物响应研究需结合可变的火活动特征与植被结构展开。本研究整合火活动与植被结构相关信息，以澳大利亚北部一处极易发生火灾的热带稀树草原（tropical savanna）为研究对象，旨在深化对蚂蚁群落响应17年控制性火烧试验（experimental fire treatments）的理解。此前一项分析显示，经过5年火烧处理后，蚂蚁群落的分化程度有限。据此，我们首先探究了后续12年火烧处理下蚂蚁群落的分化程度；随后评估了火烧处理、累积火强度以及木本覆盖度（woody cover）对蚂蚁物种出现频率、物种丰富度（species richness）与物种组成（species composition）的相对贡献。研究发现，即便经过17年的处理，火烧处理仍仅能解释极少部分蚂蚁响应变量的变异。与之形成对比的是，木本覆盖度对所有响应变量均具有极强的预测效力，而火活动则对蚂蚁多度（abundance）与物种丰富度具有中等程度的预测能力。相较于植被覆盖度较高且火活动较低（或未发生火烧）的样地，火活动水平更高的开阔生境中，蚂蚁物种的出现频率与物种丰富度均有所提升。此外，植被覆盖度高低不同的样地之间，蚂蚁物种组成存在显著差异。本研究结果为"火对动物的影响主要通过改变植被结构产生间接作用"这一原理提供了试验证据。此外，研究结果表明，"统一"的火制度（fire regime）并不会对蚂蚁动物群产生统一的影响，这是因为植被结构与火活动之间的相互作用会带来变异。这一发现有助于解释为何火多样性（pyrodiversity）与生物多样性之间往往仅存在较弱的关联，同时也降低了通过主动管理火多样性以维持生物多样性的必要性。