Welcome! Today we're going to be covering palaeoecology: applying ecological principles to the fossil record to understand past animal communities, and the rocks that host fossils.
Caspar David Friedrich - Rocky Landscape in the Elbe Sandstone Mountains
Palaeoecology is a diverse field. Some of it relies on clever anologies with living creatures, whilst some uses hardcore quantitative/computational techniques. There's a fair bit in between those two as well. I've done my best to create a narrative for you that ties this all together! I hope you enjoy it.
We're going to cover:
The ecology of fossils (palaeoautecology) – Section 5.1.
An introduction to ecology and palaeosynecology:
Ecological niches – Section 5.2 & 5.3.
Environmental gradients – Section 5.4.
Fossils as indicators of an environment – Section 5.5.
Large scale trends – Section 5.6.
Also, don't forget – coursework is due 09:00 (AM) on the 9th of November 2020.
4.1 – Palaeoautoecology
Let's start by defining terms, and then looking examples of the ecology of individual (fossil) species: how they lived their lives, and what role they played in their ecosystem. This is the world of palaeoautoecology.
We can split palaeoecology into two subfields – palaeoautoecology, described above, and palaeosynecology (the study of ecosystems in the past).
Palaeoautecology will often focus broadly on mode of life and life traits, through drawing inferences from the morphology of organisms (=functional morphology).
The inferences of functional morphology build on adaptations of organisms to the environment in which they live.
We can do this with fossil species by using organisms that are alive today as an analogy, or by using quntitative techniques.
In our zoom session for this course we'll think a bit more about trilobite modes of life, digging deeper into the mode of life of a range of species and playing with some more 3D models.
You don't need to do any preparation for this exercise, but please do come along to the zoom session to help build up your experience of palaeoautoecology!
4.2 – Ecological niches
We deal with different aspects of palaeosynecology over the next five videos! Let's start with niches. These are an important concept that explains why we find particular animals in particular environments. We'll also touch on some basics of ecology!
We can split the biosphere into a series of heirarchical categories, and there are ecospaces associated with these.
Communities occupy ecosystems; the breadth of interactions in these make them really complex.
Species occupy a niche, which we can split into their prospective and realised niche – the latter is the portion of ecospace in which a species actually lives.
The principle of competitive exclusion states that two species cannot coexist within a niche.
4.3 – Niche partitioning
The thing about niches – well, a thing about niches – is that organisms can help define their niche through their behaviour. This means that there are lots of ways in which niches can be differentiated. This is called niche partitioning – let's learn about it!
There are many ways in which niches can be differentiated.
We've met four examples:
Resource partitioning: species specialise in the resources they require (e.g. space, food) allowing them to avoid direct competition.
Predator partitioning: this relies on the differential impact of predators/pathogens that are prey/host specific.
Conditional diofferentiation: occurs when competing species differ in their ability to consume/employ a resource through varying environmental conditions.
Temporal partitioning: niches are partitioned based on timings of their activity.
(of course, if time leads to conditions changing, this could be a form of conditional differentiation, but if you consider time a resource, it is a form of resource partitioning!)
4.4 – Environmental gradients
In the real world, conditions vary in space. When they do so, this often occurs along gradients – gradual transitions across an environment. Here we meet these and see how they interact with ecological niches.
The spatial distribution of organisms and their associations are controlled by physical, chemical and biological factors which often change along gradients.
Along a gradient, within a niche, we expect organisms to have optimal conditions under a species is most successful.
This allows us to use species as, for example, bioindicators. These allow us to assess the quality of the environment.
The interaction of gradients and niches defines community distributions, but the nature of this interaction isn't clear cut.
4.5 – An example from the fossil record
Let's have a look at the impact that this interaction of niches and gradients has on the distribution of fossil groups in rocks.
The exact nature of this impact is defined by the environment and time period in which fossils were deposited: palaeontologists spend significant amounts of time building up expertise
that allows them to make nuanced interpretations of fossil assemablages, that take into account (palaeo)biogeography, environmental conditions, and fossil preservation (taphonomy).
Our next video provides a quick overview of how this all works, and can help us undesrstand the water depth in which a sediment was deposited on ancient clastic shelves: common squences of environments from beaches into the deep sea.
There are many roles fossils can play that are really useful to geologists. An important one is differentiating depositional environments.
But we do need to be aware of the biases introduced by the processes of fossilisation.
We can identify water depth in marine environments based on fossil assemblages that vary with depth, and through time.
This is true of both body, and trace fossils: but we always have to consider potential confounding factors.
4.6 – Large scale trends
Let's finish by digging a tiny bit further into some cutting edge studies that use a quantitative approach to try and remove biases from the fossil record, and look at biodiversity and ecology in deep time.
There are a number of biases that we need to be aware of: we shouldn't just assume that number of fossils species is strongly related to the true biodiversity at the time those fossils were deposited.
Using large databases, we can correct for biases.
As an example, doing so for marine environments suggests that biodiversity does not continually increase to the present (it may rather reflect the prevalence of reef ecosystems).
We can also use these approaches to understand how species respond to changes in climate.
In the latest Carboniferous, aridification reduced diversity, but increased cosmopolitanism (i.e. species became more widespread).
These insights help us understand the impact that current environmental changes might have.
None! I've kept the associated tasks light this week because in the bonus stuff section, I've linked a workshop that gives you an opportunity to actually do one of these analyses! Its very exciting and cool! So if you want to dig down deeper into today's topics (and get some experience of coding) please do invest some of your free study time giving this a shot.
As I said in the last video, I think palaeoecology, especially the computational analyses highlighted in the last video, is a fast developing and super exciting field. Here are some bonus bits if you want to read more about the latest in palaeoecology!
Those super cool papers
Let's start with links to the two papers that I used as examples. The marine biodiversity sttudy – from a team of super talented palaeoecologists – can be found here:.
Computational palaeoecology is developing fast. And there's nothing like actually doing an analysis to get a feel for a field. If, like me, you like fiddling with code, you may want to give an analysis a shot.
The above link includes all the code you need (you'll need to install R). I've put the introductory video below, so you can watch this first if this is all of interest to you. It covers the sources of sampling bias in the fossil record.
And this, second video, provides an overview of what sampling bias means for palaeontologists.
As a general note, I am not just very grateful for my colleagues who made this workshop and released it for free, but am very jealous of... you! Back when I was training as a palaeontologist, resources like this were rather harder to come by. I think it's fair to say that fewer palaeontologists, even a decade ago, used computer-based approaches. That you can do this sort of analysis on your own PC from anywhere in the world is... just super cool!
If you do try this, and get stuck, please feel free to ask for help during the zoom session or via email, and – whilst this is outside my wheelhouse – I will very happily try and help out.