Ecological network analysis: forgotten?

A new [preprint article](http://dx.doi.org/10.1016/j.ecolmodel.2009.07.012) pop up in *Ecological Modelling*'s RSS feed today, showing a case study using ecological network analysis in the functional assessment of an estuary ecosystem. I was wondering what is ecological network analysis, and how it assesses a system's function, so I read on.

It turns out that the technical details of ecological network analysis involves food web and information theory. The former I have some understanding, but the latter is too complex for me as a newcomer to dwell in the late night. [Here](http://www.fisheries.ubc.ca/files/ECOPATH%20IISoftwareForEcosystemModels%20_SmallerFileSize.pdf) is the paper describing the ECOPATH II model used by the preprint article. Judging from its number of being cited, many people must have used it successfully in their studies. However, the authors of the model acknowledged that it is based on a steady-state assumption, which arguably hardly exist in any real ecosystem, thus they recommend it used only in snapshot descriptions of ecosystems.

I doubt such a model can be used to describe ecosystem functions, considering that ecosystem functions do not present themselves in full in a "snapshot". The authors of the preprint article seem confident that this method at least identify ecosystem functions based on the goal of management defined by researchers and decision makers. But I think the role of artifacts and stochasticity in this is too significant to let pass.

In preliminary studies, I think this method has its use. If researchers can establish the food web structure and nutrient dynamics in a system, we may use this method to identify some key species or functions of the system. However, its results must be iteratively put back to our picture of the system, to check whether it conforms the dynamics and management goals. The method seems to work only with "pure" ecosystems, while many researchers have moved on to study social-ecological complex systems. I wonder if this is the reason why the method has been silent for all these years.

Christian, R., Brinson, M., Dame, J., Johnson, G., Peterson, C., & Baird, D. (2009). Ecological network analyses and their use for establishing reference domain in functional assessment of an estuary Ecological Modelling DOI: 10.1016/j.ecolmodel.2009.07.012

Christensen, V., & Pauly, D. (1992). ECOPATH II — a software for balancing steady-state ecosystem models and calculating network characteristics Ecological Modelling, 61 (3-4), 169-185 DOI: 10.1016/0304-3800(92)90016-8

Bodélé: "More or Less" a major dust source

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Recently I am help doing a study on dust transport and deposition
concerning central and northern Libya. [A geochemical study](http://dx.doi.org/10.1016/j.atmosenv.2006.02.020) by my mentors suggest
that some of the dust in Hun and Sebha, even some in the coastal
areas, may be from the Bodélé, which is the largest source of dust in
Libya. [This preprint article on
PNAS](http://dx.doi.org/10.1073/pnas.0711850106), therefore, is of
special interest to me.

However, if the authors of the paper are right about the transport
mode of dust from Bodélé, our story may prove wrong. The authors
claim that the prevailing direction of the dust transport from this
area is towards the west in winter, which is also the maximum of dust
output in a year in the area. But our study area shows a constrasting
trend: lowest dust deposition both by ground data and remote sensing,
in winter, and it is to the north of Bodélé. The summer
transportation, if any, may contribute very little to our study area,
limited both by transport and production.

The MODIS brightness temperature difference (BTD) data is being
derived, which can provide us a picture of dust plumes for major dust
events. We are also looking at the geochemical properties and
meteorological data around the area. Combining these data, hopefully,
can provide more information on the transport mode in our study.

In the PNAS paper, the authors point out that the Bodélé area may be a
"tipping element" in the context of climate change, due to its
dominant position in the output of dust and its location. Some
climate models suggest that the area may become wetter, yet the wind
will be strengthened. As a result, it is really difficult to tell how
the dust output will be influenced by climate change at the moment.
Will we have more or less dust from Bodélé? This will be an
interesting problem, as dust from this area interacts with many
large-scale systems. It is a wonder, considering that the Bodélé
Depression is so small. The difficulty is that we only have inaccurate
model and incomplete data for this area, and for the North Africa.
New remote sensing technology such as
[SEVIRI](http://www.esa.int/esapub/bulletin/bullet111/chapter4_bul111.pdf)
(imagine quasi-MODIS resolution images every 15 minutes, very cool) may partly solve
the problem, but more geochemical and meteorological data are
essential to answer the complex dust question.

Washington, R., Bouet, C., Cautenet, G., Mackenzie, E., Ashpole, I., Engelstaedter, S., Lizcano, G., Henderson, G., Schepanski, K., & Tegen, I. (2009). Tipping Elements in Earth Systems Special Feature: Dust as a tipping element: The Bodele Depression, Chad Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0711850106

OHARA, S., CLARKE, M., & ELATRASH, M. (2006). Field measurements of desert dust deposition in Libya Atmospheric Environment, 40 (21), 3881-3897 DOI: 10.1016/j.atmosenv.2006.02.020

Some like it hot ... or variable

I have the impression that someone on researchblogging.org has already used a similar title to describe the link between rising temperature and vectors of contagious diseases. But [this article](http://dx.doi.org/10.1073/pnas.0903423106) has pointed out another layer of complexity existing in the temperature-disease connection. Turns out that malaria does not necessarily need hot weather, a reasonably warm mean temperature with high diurnal temperature range (DTR) will do.

The malaria parasites will need to develop to a certain stage before it can actually infect people. And this takes time. Researchers already know that the length of the period depends on the environmental temperature, and accordingly they predict that the risk of malaria epidemics will increase, as the mean temperatures in many areas rise. It takes less time for the parasite to develop, and the carrier -- mosquitoes -- has more time to bite and infect people before it dies. If the period of development is so long that it almost equals or even exceeds the mosquito's life expectancy, very little harm is done.

The authors of the PNAS paper find that the period of development depends not only on daily mean temperature, but also on the temperature range through the day. In areas with relatively low temperature, given the same mean temperature, malaria parasites in areas with higher temperature variation in a day need significantly shorter time to develop. Similarly, high DTR in areas with high temperature may slow down the development. Thus the authors say the picture of malaria and similar epidemic in a global climate change context may be more complex than we previously think.

The immediate lesson is that we may have overestimated the additional risk in some tropical areas, and underestimated that in some temperate regions. But exactly what are these areas asks for studies at local scale.

Paaijmans, K., Read, A., & Thomas, M. (2009). Understanding the link between malaria risk and climate Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0903423106

与一个智能设计论者(?)的对话

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今天从超市回来的时候, 在路上被一个慈眉善目的老爷爷拦住, 问我是不是本市
大学的学生, 然后又问我学的专业. 知道了我学地理并是个二把刀的生态学学生
以后, 我们就开始聊人类对环境的破坏问题.

在英国呆过一段时间的同学都知道, 一般在街上找人说话的, 通常不是传教的就
是代表某慈善组织劝你捐钱的, 或者这两者的交集, 但是我实在太久没跟英国人
说过话了, 心想说两句也是好的, 就扶着自行车, 背着菜篮子, 在步行街中间和
他聊起来.

老爷爷感叹了一番人类对环境的破坏, 痛斥了超市里连个苹果都要从南非千里迢
迢运来的不合理性, 然后回忆了自己小时候自己种土豆吃的时光. 但是我很不解
风情地说, 要是人人都自己种土豆吃, 那谁有空办学校和读书呢? 老爷爷就乐了.
我背的是个布口袋, 老爷爷大概没看出我刚从超市出来. 其实我口袋里就装了一盒
美国产的樱桃, 说出来怪囧的.

老爷爷接着说，你说几千年前人就知道水循环的道理了，怎么进化了几千年，反
而越发贪婪和不爱地球了呢. 我心说进化几千年算个啥. 然后我说别说几千年,
物种争夺资源的天性是始终伴随着进化的, 人类的这个问题比较突出不过是因为
人跟生态系统解耦的程度高一些而已. 何况进化一词字面上暗示进步, 其实方向
是随机的, 变化也无所谓好坏, 只有能否适应环境的区别而已.

老爷爷又自顾自地说, 你看啊, 你说到进化, 进化是有条件的, 如果没有数亿年
持续不断的水循环, 进化的历史是不可能的. 而水循环和太阳带给我们能量的过
程, 这是多么精巧的设计啊! 我心里暗叫不好, 该不会是宣传 ID 的吧, 不过不
好立即就给人家扣上这么一顶帽子, 如果他是正统的神创论者大概也不乐意被当
作 ID 论鼓吹者, 于是我就继续跟他聊下去.

然后他就把书拿出来了. 英国的天气一个特别有利于传教的地方在于, 夏天经常
不热, 穿个大衣出来也不是特别奇怪, 于是你就不知道什么时候他们会突然 biu
地一下变出一本<圣经>或者别的什么书要你看. 我随便翻了一翻, 不能确定是神
创论还是 ID, 但基本是否定进化论的. 于是我就拿着书跟他讲进化论的理论和证
据等等. 另外还扯了一堆月球火星之类有的没的. 然后我说我不反对作为对精神
世界的探求的宗教, 科学有它需要解答的问题, 宗教也有它要解决的问题, 而如
果它们跨界试图解决它们领域之外的问题, 结果很可能是可怕的. 当时没想起好
的例子, 就随便说了人的平等与差异如果完全试图用科学来解释, 结果就是给纳
粹式的优生学张目, 其实如果举人的感情不能简单地用科学还原为激素和神经元
的相互作用这个例子, 可能更能说明这个道理. 我借用了 Contact ¹的立意,
即完整的真相需要科学和宗教携手去发现, 这也是 Short Introduction 系列
Science and Religion ²的观点. 没想到老爷爷提醒我历史上因宗教而杀人
的事例不少. 于是我怀疑他信 ID, 虽然当时我没多想.

后来又杂七杂八聊了一堆, 比如达尔文写<物种起源>与他的信仰问题, 还有上帝
与自然规律的关系等等. 眼看将近正午, 老爷爷知道没法说服我, 就收起书走了.
我们友好地互道再见.

我现在还是不能确定, 或者不愿承认, 这位老爷爷是主张 ID 的. 我看过主张在
学校科学教育中引入 ID 的书³, 其作者们虽然号称是大学教授, 写出来的
文字却未必比这位老爷爷的话更理性. 老爷爷至少在言谈中表现出了对事实的尊
重, 哪怕这与他相信的东西不一样. 这次对话更像是表达意见而非交锋.

虽然谈话没有改变我们双方的不同看法, 但是不难想象这样一位书卷气浓厚的老
爷爷要说服没有经过系统科学教育, 或者自己对这类问题思考不多的人会是多么
容易. 失败的传教和失败的科学教育, 共同点在于它们一上来就要求记诵它们所
宣称的真理. 老爷爷的传教没有成功, 则在于他试图用我的专业拉近我与他的观
念的距离, 但我的知识储备让我能够看出他的话语中牵强附会的地方. 我不知道
什么是成功的传教, 但它大概要建立在社会所接纳或追求的价值体系之上, 这个
价值体系因时期而异, 中世纪是忠君爱王, 现在讲究自由意志, 但大体上脱离不
了基本的道德原则. 成功的科学教育, 大概也需要类似的一个价值体系, 但科学
本身是没有道德性的, 所以这个体系的建立会困难一些. 但科学教育有一个优势,
在于人的求知欲可说是与生俱来的, 后天要掌握的不过是描述现象, 提出假设和
证明的方法, 这些相对来说都是比较容易规范化的. 于是乎, 科学教育所需要的
价值体系的基础, 我想可以建立在 1) 对自身认知能力和局限的认识; 2) 对现象
的准确描述; 3) 对理论的产生, 作用和局限性及谬误的认识和相关的实践; 4)
作为生产活动和文化的科学; 以及 5) 科学与现实世界的联系这 5 个逐级拔高的
支点上.

Footnotes:

¹ http://www.imdb.com/title/tt0118884/

² http://www.douban.com/subject/3148421/

³ http://www.douban.com/subject/2830831/