Predation risk for reptiles is highest at remnant edges in agricultural landscapes

Preventing biodiversity loss in fragmented agricultural landscapes is a global problem. The persistence of biodiversity within remnant vegetation can be influenced by an animal's ability to move through the farmland matrix between habitat patches. Yet, many of the mechanisms driving species occurrence within these landscapes are poorly understood, particularly for reptiles.
We used scented and unscented plasticine lizard models and wildlife cameras to (a) estimate predation risk of reptiles in four farmland types (crop field, pasture paddock, restoration tree planting and areas with applied woody mulch) relative to the patch edge and remnant vegetation, and (b) examine how predation risk was influenced by temporal change in the matrix (crop harvesting).
Birds (55.1%), mammals (41.1%), reptiles (3.4%), and invertebrates (0.5%) attacked models, of which 87% were native species. Mammalian predators were 60.2% more likely to attack scented models then unscented models. Bird predators were not influenced by scent.
We found predator attacks on models were highest at edges (49%, irrespective of adjacent farmland type, with a reduced risk within farmland (29%) and remnant patches (33%) (p < 0.01). Both mammal and bird predators contributed to high numbers of predation attempts at edges.
Removal of crops did not increase predation attempts in crop fields or other farmland types, although predation attempts were significantly lower along the crop transect after harvesting, compared to the woody debris transect. However, numbers of predation attempts were higher in edge habitats, particularly prior to harvesting.
Synthesis and applications. Reptiles are at risk of predation by birds and mammals in both remnant patches and the farmland matrix, particularly in edge habitat. Our results demonstrate that edge habitats are potentially riskier for lizards than the farmland. Vulnerability to predation may be increased by a lack of shelter within edge habitats such as by increasing visibility of reptiles to predators. Therefore, to benefit reptiles, land managers could provide shelter (rocks, logs, and grasses), particularly between remnants and linear plantings which could improve landscape connectivity.

破碎化农业景观中的生物多样性丧失（biodiversity loss）防控是一项全球性难题。残存植被（remnant vegetation）内的生物多样性存续状况，会受到动物在生境斑块（habitat patches）间穿越农田基质（farmland matrix）移动能力的影响。然而，目前学界对驱动这类景观内物种出现的诸多机制仍知之甚少，针对爬行动物的相关研究尤为匮乏。
本研究采用带气味与不带气味的橡皮泥蜥蜴模型（plasticine lizard models），配合野生动物相机（wildlife cameras）开展两项实验：（a）对比斑块边缘（patch edge）、残存植被区域，评估四种农田类型（农田（crop field）、牧草地（pasture paddock）、修复性植树区（restoration tree planting）及施用木质覆盖物的区域（applied woody mulch））内爬行动物的捕食风险；（b）探究农田基质的时间变化（crop harvesting，作物收获）对捕食风险的影响。
攻击模型的类群依次为鸟类（55.1%）、哺乳类（41.1%）、爬行动物（3.4%）与无脊椎动物（0.5%），其中87%的攻击者为本土物种（native species）。哺乳类捕食者（mammalian predators）攻击带气味模型的概率比无气味模型高出60.2%，而鸟类捕食者的攻击行为不受气味因素影响。
研究发现，模型遭遇捕食攻击的概率在斑块边缘最高（49%，不受相邻农田类型影响），农田区域（29%）与残存植被斑块（33%）内的捕食风险均有所降低（p < 0.01）。哺乳类与鸟类捕食者均是斑块边缘高捕食攻击频次的主要贡献者。
尽管收获后农田样带（transect）的捕食攻击频次相较木质碎屑（woody debris）样带显著降低，但作物移除并未提升农田或其他农田类型内的捕食攻击频次。不过，边缘生境的捕食攻击频次整体更高，尤其是在收获前阶段。
综合与应用。爬行动物在残存植被斑块与农田基质中均面临鸟类与哺乳类的捕食风险，尤以边缘生境为甚。本研究结果表明，相较于农田区域，边缘生境对蜥蜴而言潜在风险更高。边缘生境缺乏遮蔽物会提升爬行动物被捕食者发现的概率，进而加剧其被捕食的脆弱性。因此，为保护爬行动物，土地管理者可在残存斑块与线性种植带之间增设遮蔽物（石块、原木与草本植被），以提升景观连通性（landscape connectivity）。