Parasites and Communities; Empirical and Theoretical Scaling

寄生虫引起了生态学家的兴趣，因为它们通过使动物生病，改变了这些动物与自然群落中其他物种的互动方式。我们研究了两种本地和入侵对虾的寄生虫，发现寄生虫改变了一种虾吃另一种虾的频率(这一过程被称为行内捕食)，以及它们选择捕食的其他类型的猎物。此外，虾可能会对被捕食者(鱼)吃掉的威胁做出反应，变得不那么活跃，因此潜在地不太可能吃掉其他动物。现在的挑战是研究这些影响对更广泛的社区的后果：寄生虫和捕食者如何影响我们在社区中发现的物种，以及它们的常见程度。我们将使用实验室和野外实验，以及数学来研究这个问题：首先，建立寄生虫和捕食者如何影响两个或三个物种之间的互动的图景；其次，研究这些影响如何改变群落中其他物种之间的关系。1.我们将研究寄生虫如何影响捕食行为，例如利用实验室实验来测量在有和没有捕食者线索的情况下，受感染的虾与未感染的虾相比的功能反应(捕食者对猎物的消耗率和猎物密度之间的关系)。这将帮助我们建立寄生虫改变宿主功能反应的数学模型，这样我们就可以研究行为改变如何影响种群动态(种群大小随时间的变化)。2.我们将使用自然对虾种群的稳定同位素分析(通过测量化学变化来告诉我们动物的饮食)，以确定寄生虫是否会导致宿主饮食的变化。我们还将通过实验室实验来研究这一想法。我们将建立一个数学模型，将寄生、捕食和行内捕食的相互作用联系在一起，并利用这个模型来研究涉及的物种的种群动态，并看看寄生诱导的功能反应和饮食的变化是否可以改变群落结构。我们的发现将引起其他科学家的兴趣，他们关注寄生虫对物种之间相互作用的影响，以及它们对更广泛的社区和环境的影响。它还将使管理自然栖息地、多样性和入侵的机构感兴趣(环境署；北爱尔兰环境局，农业和农村事务部，北爱尔兰)。研究寄生虫很重要，原因有很多。首先，由于它们通常是群落的“隐藏”成员，并且不经常杀死寄主，与物种之间的其他相互作用(如捕食和竞争)相比，它们的影响被忽视了。然而，它们可以对群落产生戏剧性的影响，改变相互竞争的物种之间的平衡，有时允许两个物种共存，如果没有寄生虫，其中一个物种就会灭绝(这使寄生虫成为“关键物种”)。其次，寄生虫经常参与外来物种对新环境的生物入侵；在许多情况下，入侵物种造成的损害更大，因为它没有被该环境中的寄生虫感染得那么严重，或者它引入了新的寄生虫，导致当地物种的疾病/死亡。事实上，在我们的研究系统中，有一种虾是入侵物种，我们热衷于了解推动其成功的力量，以便我们能够更好地保护本土物种。第三，寄生虫具有重要的公共卫生和经济后果：紧急疾病(跨越物种边界感染新物种的寄生虫)对人类健康、家畜和野生动物的威胁越来越大。这个项目将通过改善我们对寄生虫在自然社区中的影响的了解来帮助理解这些重要的问题。

Parasites interest ecologists because, by making animals ill, they alter how those animals interact with other species in natural communities. We have studied the parasites of two species of native and invading shrimps and found that parasites alter how often the shrimp of one species eat the other shrimp species (a process called intraguild predation), and the other types of prey that they select to eat. In addition, shrimp may respond to the threat of being eaten by predators (fish) by becoming less active and so potentially less likely to eat other animals. The challenge now is to study the consequences of these effects for the wider community: how parasites and predators influence which species we find in the community and how common they are. We will use lab and field experiments, and mathematics to look at this problem, to: firstly, build up a picture of how parasites and predators affect interactions between two or three species; secondly, examine how these effects alter the relationships between other species in the community. 1. We will examine how parasites affect predation, for example using laboratory experiments to measure the functional response (the relationship between a predator's consumption rate of prey and the density of the prey) for infected shrimp compared with uninfected shrimp in the presence and absence of predator cues. This will help us build mathematical models in which parasites alter their hosts' functional responses so that we can investigate how behaviour modification affects population dynamics (changes in population size over time). 2. We will use stable isotope analysis (which measures chemical variation to tell us about an animal's diet) of natural shrimp populations to see whether parasites cause a shift in host diets. We will also investigate this idea using laboratory experiments. We will build a mathematical model that links together the interactions of parasitism, predation, and intraguild predation, and use this to investigate the population dynamics of the species involved and see whether the parasite-induced changes in functional responses and diet that we expect to find in the shrimp community can change community structure. Our findings will be of interest to other scientists concerned with the impact of parasites on interactions between species, and their impact in the broader community and environment. It will also interest agencies who manage natural habitats, diversity and invasions (Environment Agency; N. Ireland Environment Agency, Department of Agriculture and Rural Affairs, N. Ireland). It is important to study parasites for many reasons. Firstly, as they are often 'hidden' members of the community, and do not often kill their hosts, their effects have been neglected compared to other interactions between species (such as predation and competition). Nevertheless, they can have dramatic impacts on communities, altering the balance between competing species, sometimes allowing two species to coexist where one would go extinct if parasites were not present (this makes the parasite a 'keystone species'). Secondly, parasites are often involved in biological invasions by foreign species into a new environment; in many cases an invading species does more damage because it is not as badly infected by the parasites in that environment, or it introduces new parasites that cause illness/death of the native species. Indeed, in our study system, one of the shrimps is an invading species and we are keen to understand the forces driving its success so that we can better protect the native species. Thirdly, parasites have important public health and economic consequences: emergent diseases (parasites that cross the species boundary to infect a new species) are an increasing threat to human health, domestic animals and wildlife. This project will help to understand these important problems by improving what we know about the effects of parasites in natural communities.