What are the key ecology concepts all Intro Bio students should learn? (2024)

When I started at Georgia Tech, the “large” (80-90 student) course I was involved in was General Ecology. My first year there, I co-taught the course with my colleague Lin Jiang. I did what is probably fairly typical: I asked him for the materials he used when he last taught the course and then modified those. So, it was pretty eye-opening to me when, after that first semester, we (“we” being the people involved in teaching General Ecology and related courses) decided that we should try to assess what our students were learning. We couldn’t find a good ecology concept assessment*, so we decided to try to create our own. That involved deciding what the key concepts were that we wanted all students who had completed ecology to know. Coming up with that list was incredibly useful and changed the way I taught the next time.

I’ve been thinking about this again as I spend more time thinking about how to teach ecology to introductory biology students here at Michigan. I’ve thought about this before – we recently overhauled the course, and that involved a lot of thought about what to teach. But I feel like I want to think more about the core concepts again. I wantto revisitthe core ecology concepts that my GaTech colleagues and I came up with for a sophom*ore-level (that is, 2^nd year) ecology course and figure out how to modify those for a freshman-level (that is, 1^st year) course. With this post, I’m hoping to think more carefully about what the core concepts are, and to get feedback from others about the list I came up with.

First, I’ll explain a little more about the Intro Bio course I teach. It is a large enrollment (~550 students per semester) course, with many first-semester freshmen in it. In my experience, most of these students have had no prior exposure to ecology. (Something I am very interested in doing is better assessing what they know about ecology when they start the course. My impression is that many of them think that ecology is pretty much just David Attenborough videos.) The one-semester course covers ecology, evolution, and genetics, so we’re pretty constrained in terms of the amount of time we have to devote to any one thing. For that and other reasons, I am definitely in favor of covering less material more deeply.

Second, I want to explain my motivations for considering this a little more. Some of them are big picture. In light of the current political climate in the US, I’ve been thinking more about what I should be doing differently in my class. As I said, for many of my students, this is their first exposure to ecology as a science. What do they need to learn to be informed citizens – for example, to be able to evaluate the information they hear about global climate change?**

But there are also less lofty motivations. In trying to be consistent about how we teach things across semesters, we sometimes email about a particular topic. This recently happened with ecosystem engineers, including a discussion about specific examples that we should or should not use. My response to that email thread was to wonder why, given the very limited time we have to cover ecology in this course, we are teaching about ecosystem engineers at all. Is it one of the most foundational topics to teach?***

With that background, I’ll now move on to present the list from Georgia Tech (which, again, was designed for a higher level course), then will list the general topics I currently teach in Intro Bio, and then will give my ideas for a list of core ecology concepts to cover in Intro Bio.(Brian did a polla couple of years ago on what an upper level community ecology course should cover.)

The list from Georgia Tech for a 2^nd year course (note: this list was a collaborative effort by several ecologists at Georgia Tech):

1. Organisms are adapted to their environments, but are constrained by tradeoffs. In addition, genotypes differ in their specific ecological requirements.
2. The distribution and abundance of a species is determined by its niche, dispersal patterns, and interactions with other organisms.
3. Populations grow exponentially (or geometrically) at first, but growth is eventually constrained by density dependence.
4. Changes in population size reflect the sum of births, deaths, immigration, and emigration.
5. Individuals, populations, and communities are affected by both the physical environment and by interactions with other organisms.
6. Competition, predation, parasitism, and mutualism are the four major types of interspecific interactions that structure communities.
7. Competition occurs between individuals (of the same or different species) that share a common resource; competitive exclusion can be the result.
8. Succession is the change in species composition over time and results from both abiotic and biotic factors, and disturbance regimes.
9. Species richness is influenced by variation in species pools, colonization rates, abiotic conditions, and species interactions.
10. Species richness is expected to be greatest at intermediate levels of disturbance; species richness at low levels of diversity is limited by interspecific competition. (I think reading that just caused Jeremy to have a heart attack. Or maybe it means he’ll no longer want to blog with me. Probably both. It’s been fun, folks.)
11. The sun is the ultimate source of energy for most ecosystems; primary production by autotrophs provides the energy for all ecosystems.
12. Ecological systems show high degrees of connection, but species do not exist for the benefit of each other.
13. Food webs reflect trophic interactions among organisms; the degree of connectivity and redundancy of food webs determines their resilience.
14. Nutrients cycle repeatedly through an ecosystem, whereas energy flows through an ecosystem.
15. Adding or removing a keystone predator can have dramatic consequences for the entire food web.

(I can’t remember if we intentionally limited ourselves to 15 concepts or if that’s just the way it worked out.)

Right now, I think the most glaring omission from the above list is something that relates to climate. I would like students to understand how we know that the climate is changing rapidly and that humans are responsible.

Okay, moving on to the list of the general topics I aim to cover in Intro Bio.**** When I taught Intro Bio last fall, the lectures I taught (80 min each) were:

1. Behavioral ecology
2. Fossil record, history of life, and human evolution (yeah, that’s not too much to cover in 80 minutes!)
3. Population ecology
4. Species interactions I: predation, parasitism, and herbivory
5. Species interactions II: competition and mutualism
6. Food webs, indirect effects, and trophic cascades
7. Broad scale patterns of diversity
8. Emerging infectious diseases & viruses (you could certainly argue this is disproportionate coverage for diseases, but I think they are a great way to cover a lot of fundamental concepts in a way that is engaging to students)
9. Ecosystem ecology I: energy flow & productivity
10. Ecosystem ecology II: nitrogen and phosphorus cycling
11. Ecosystem ecology III: carbon cycling and global climate change
12. Human impacts on evolution
13. Human impacts on the environment

Certainly there’s the potential for shifting things around there. This year, they split topic 2 into two lectures, which makes a lot of sense. (I don’t remember now what was condensed to make room for that shift.)

Okay, so, now for my list of key ecology concepts to teach at the Intro Bio level (note that I’m skipping the ones that are primarily evolutionary). For this, I’m mostly modifying the list for a higher level course that my GT colleagues and I came up with, but I’m also adding in things based on what I’ve taught over the past few years, based on this CourseSource Ecology Learning Framework (see the first footnote below for more), and based on comments on this old blog post of mine on recent major conceptual advances in ecology.

Key Ecology Concepts for First Year College Students:

1. Organisms are adapted to their environments; species differ in their specific ecological requirements.
2. The distribution and abundance of a species is determined by the physical habitat, dispersal patterns, and interactions with other organisms.
3. Populations grow rapidly at first, but growth is eventually constrained by density dependence.
4. Changes in population size reflect the sum of births, deaths, immigration, and emigration.
5. Competition, predation, parasitism, commensalism and mutualism are the five major types of interspecific interactions that structure communities.
6. Competition occurs between individuals (of the same or different species) that share a common resource; competitive exclusion or evolution can result.
7. Positive interactions such as mutualism are common in nature; with mutualisms, each partner pays a cost for participating, but the benefits outweigh the costs
8. Predator-prey and host-parasite interactions can influence behavior, vital rates, population sizes, and evolution.
9. Adding or removing a keystone predator can have dramatic consequences for the entire food web.
10. The number and kinds of species in an area change over short periods of time, as a result of abiotic factors (including disturbances) and biotic factors; this is known as succession.
11. The number and kinds of species in an area change over long (geologic) periods of time, as a result of abiotic factors and biotic factors, including speciation and (mass) extinctions.
12. Human activities are causing the number and kinds of species in particular areas to change dramatically, through habitat modification, exploitation, the movement of species, and extinctions.
13. Species richness is influenced by variation in species pools, colonization rates, abiotic conditions, and species interactions.
14. Humans use biodiversity in many different ways, including for aesthetic value, food, drug discovery, ecosystem services, and bio-inspired design.
15. The sun is the ultimate source of energy for most ecosystems; primary production by autotrophs provides the energy for all ecosystems.
16. Ecological systems show high degrees of connection, but species do not exist for the benefit of each other.
17. Food webs reflect trophic interactions among organisms; changes in abundance at one trophic level can be reflected in changes in abundance of organisms at other trophic levels.
18. Nutrients cycle repeatedly through an ecosystem, whereas energy flows through an ecosystem.
19. The climate is changing rapidly due to the burning of fossil fuels by humans; this is expected to have profound consequences for many species.
20. Many ecological processes and interactions are mediated by microbes.
21. Evolution can happen on contemporary timescales, with important consequences for ecological interactions.

That’s my first crack at it. 21 is probably on the high end, but, with 13 80-minute class periods, that works out to about 50 minutes per concept, so I don’t think it’s toomany. (We also have one discussion a week where we work on especially challenging concepts, like “energy flows but matter cycles”.) I would love to hear suggestions for things to add or to remove (but if you suggest something to add, it would be good to suggest what to remove!) What do you think are the most important concepts to cover with students in their first exposure to ecology? How would your list differ from the one I laid out?

* I know that Michelle Smith’s group at Maine has been working on one. I’m really looking forward to seeing the final version! And I recently learned about this CourseSource Ecology Learning Framework which was created by some ESA members (specifically: Jennifer Doherty, Diane Ebert-May, and Bob Pohlad).

** Related to this, I’ve realized that I need to change what I teach when I talk about human evolution. I am much less concerned that they know the shared derived traits of hominids than that they are able to evaluate claims related to biological aspects of race.

*** I could make arguments in either direction on this, but, right now,I think ecosystem engineers are probably not something I will teach about in Intro Bio in the future.

**** There are skills I want them to acquire, too – especially how to read figures and how to think evaluate information they are presented with. I also would like for them to develop a general appreciation for and understanding of biodiversity. I think we’re doing a pretty good job with helping them to develop figure-reading skills. I don’t think we do a great job with biodiversity at the moment.