Download Lecture Notes: Lecture 1 (Based on Chapter 1 of Cain et al. 2014

Lecture Notes: Lecture 1
(Based on Chapter 1 of Cain et al. 2014).
Case study of malformed frogs
- Each chapter in the textbook has a “case study”. It is an interesting story or example related to the
theme of the chapter.
- In this first chapter, the case study is about amphibians, and strange observations of frogs found in the
wild with too many, or severally malformed, limbs.
- This discovery first gained publicity (attention in news) in 1995 when school children in Minnesota
(USA) found many malformed amphibians on a fieldtrip to a lake.
- But the textbook explains that scientists had been making similar observations since the 1980’s.
- One explanation was that a trematode worm inside the frogs, named Ribeiroia ondatrae, interfered
with the frog’s developing limb buds, causing these problems.
- In 1999, Johnson and colleagues published a paper showing the results of observational work
(observations made on a scientific topic without manipulation of any factors) and an experiment.
- Their observational work showed at deformities were found in only 4 of 35 ponds they examined, and
all of these 4 ponds were inhabited by a snail. This snail is a host of Ribeiroia. That is, the worm has a
complex lifecyle, living for some time in the snail before having a free swimming life stage in which it
enters frogs. Then when frogs are consumed by aquatic birds, the worm grows insides the birds until it
lays eggs that are expelled in the birds’ feces, and turn into very small larvae that attach to snails and
start the life cycle again. See slide 7.
- In their experimental work, “Johnson et al.” (Johnson and colleagues) had different treatments, with
different levels of Ribeiroia, including 0 worms (which would be considered the control; no
manipulation). As the number of Ribeiroia increased, so did the amount of frog malformations, while the
survival of the frogs decreased.
- But is the story this simple? The textbook explains that the observation about frog malformations was
made at a time when people were recognizing that frog populations, all over the world, were decreasing.
People were asking whether frogs were in some way affected more by human activities than other
animals, because their skins are permeable (chemicals including toxins can get through their skin).
- In 2002, Kiesecker et al. reported on a more complex experiment. In this experiment they had 6 ponds,
3 with pesticides (chemicals that are sprayed on agricultural crops to control destructive insects) and 3
without. In each pond they had two kinds of cages which kept frogs. One kind of cage had small mesh
that did not let Ribeiroia in, and the other cage had mesh that was bigger and let the worms in. What
are the controls for this experiment?
- Kiesecker found that the frogs with the big mesh in the cages in ponds that had pesticides developed
more malformations. They concluded that pesticides could increase the possibility that frogs developed
these malformations (caused by the worms) by decreasing the frogs’ immune systems.
- In 2007, Johnson et al. reported a further complication: in areas with run-off from agriculture (fertilizer
used on agriculture gets into water supply), a lot of algae develops in ponds, increasing the number of
snails, and thereby Ribeiroia and frog malformations.
- From this case study, we conclude that in ecology everything is connected (and complicated!). For
example, increases in algae can increase the number of snail. Or changes in one factor (amount of
pesticides) can influence another process (worms making deformations in frogs). And ecology is
fundamentally about solving mysteries – and hence interesting and fun!
What is ecology?
- The textbook defines ecology as the science probing connections (or interactions) between organisms
and their abiotic (non-living) and biotic (living) environment.
- Why does it stress that ecology is a science?
- In class (more than the textbook) we reviewed the steps in the scientific method:
- To ask a good question, having learned about previous research.
- To have a hypothesis, which is a testable idea, and leads to predictions of what exactly will
happen under certain conditions.
- To design methods that will test the hypothesis in an objective (not biased) way.
- To gather data following the methods.
-To draw conclusions using the data and statistical analysis in an objective way and then to
communicate those conclusions. We talked about how in science each individual just lays one brick in a
big wall, but because it is communicated it can be used by many others.
- We also talked about the different kinds of scientific studies: there can be purely descriptive studies,
observational ones, experimental ones, and ones that are purely mathematical like making
mathematical models.
- Again, we stress the difference between an observational study, which looks at the relationship, or
correlation, between two factors, and an experiment, which can demonstrate that one factor causes the
other.
- We then looked at some features of an experiment:
- It has a control or controls, where the factor of interest is not manipulated. In contrast, in
other treatments the factor is manipulated.
- The subjects that are treated are assigned at random to a treatment. For example, people are
assigned to different medical treatments (drug vs. placebo, the control) randomly, not by people,
because people could have some nonrandom preferences that would confound the experiment
(make the results unclear).
- The methods are replicated on many subjects. Replication allows us to see how stable the
results are and is crucial for statistical analysis.
- Statistical analysis is a way of objectively interpreting the results of the experiment. It
compares what happened in the experiment to what might be expected by chance, and gives us
a probability that the result was merely a chance effect. If this probability is low, we think that
the factor of interest is “significant”, or important to explaining the result.
- We also talked about several qualities of ecology as a science:
- I) The first is that ecology covers a wide range of levels of organization. Hence there are different kinds
of ecology focusing on:
- The individual. Looks at how an organism interacts with its environment. It looks at how the
characteristics of the organism are adapted (fit, as a result of evolution – see later lectures) to
the environment.
- The population. A population is a group of organisms of the same species. Population ecology
looks at how qualities of the population (size, distribution, growth) are connected to the
environment.
- The species. A species is a group of organisms that are able to reproduce with each other.
- Species interactions. The ecology of species interactions look at relationships between species:
whether one species eats another (predation), competes with another, harm another without
killing it (parasitism), interacts with another without harming or benefiting (commensalism), or
how a pair of species benefits each other (mutualism).
- Community. A community is a group of species at one particular time and place. How does the
diversity of species vary among communities?
- Ecosystem. An ecosystem includes all the living organisms in a given area as well as the
physical environment where they live. Ecosystem ecology looks at how energy, nutrients move
between components of the ecosystem.
- Landscapes. Landscape ecology looks at interactions between ecosystems in space, and can be
small (a town) or large (a whole region like Asia).
- Global. Ecology that looks at the world as a whole. An example is studying climate change,
which affects the earth as a whole. Or looking at how the diversity of communities varies by
latitude.
II) Another feature of ecology is that it deals with a wide variation of scales. For example, in terms of size,
ecologists can study how organisms make their homes (like a beehive) or how a desert like the Sahara is
increasing in space. And this range of scales can also be found in time. Some paleobiologists (scientists
who look at fossil animals) study changes over millions of years, whereas others look at daily changes,
like the ‘vertical migration’ of plankton up and down in the ocean everyday.
III) Finally, ecology is often applied as a science to understand how humans are disturbing the natural
world, and how such disturbances can be managed.
- The rest of the lecture is mostly fully described in the slides: our class objectives and evaluation (see
also the syllabus), my background, and then the kinds of jobs that ecologists can do.
- For that final section on how you can use ecology, it is useful to distinguish between ecology and
environmental science. Environmental science is a bigger field that includes ecology and focuses on how
humans change the natural world and how to manage that. It also includes social science (such as policy,
law).
- Environmental science is one way kind of the application of ecology (its practice to solve real world
problems). Other kinds include: conservation ecology, restoration ecology, and natural resource
management, as fully described on Slide 55.