Assessing millennial-scale community dynamics using mammal and vegetation food webs 

Our inaugural blog post is by Dr. Jessica Blois at UC Merced, who is overseeing the small mammal portion of our project.

Welcome to our new project website! To get things started, we thought we’d first describe the what, why and how of our project. In future posts, we’ll explore these topics in more depth.

What are we doing?

We are reconstructing ice age food webs for the mammals and plants found in the La Brea tar pits. Food webs describe connections in nature – in other words, they are networks describing who eats whom in ecosystems. As part of this project, we are focusing on small mammals and plants at La Brea, which haven’t received as much attention as the larger animals such as dire wolves and sabertooths. Once we fill in the gaps in the fossil record, we will then see if the connections in our food webs can predict which species went extinct at the end of the last ice age, and determine how resilient species were to climate change and human impacts.


A wall of dire wolf skulls at the La Brea Tar Pits and Museum (left) and a close up of the asphalt matrix with lots of tiny bones from smaller animals and bits of plants (right). Lots of attention focuses on the extinct large mammals, such as the dire wolves, but the small mammals and plants are equally as important to the overall ecosystem.

Why are we doing it?

Today’s ecosystems face many different challenges, including those from climate change and land use. Many of Earth’s species already have become extinct, and even those species that are not in immediate danger have become much more rare or have disappeared from regions they once inhabited. And, many species have been introduced to places where they never used to occur. Overall, ecosystems today may be very different than what they looked like just several hundred years ago. Unfortunately, we don’t have a good sense of what this reshuffling does to ecological communities in the long-term.

Part of the challenge in predicting how ecosystems respond to climate change is that nature is very complex. Species form a web of interconnections with one another: some of those connections are very strong (such as a plant that is dependent on one particular bee for pollination), but most of the connections between organisms are weak. We think complexity is a good thing- it likely buffers an ecosystem against disturbances – but we don’t know just how much of a buffer there is before a given ecosystem starts to break down. We’d like to get a sense of which species and connections within the food web are most important for making ecosystems more resilient to change, so that we can understand how we can help ecosystems be more resilient in the future.

How are we doing it?

The first thing that we need to do is to figure out exactly which species of plants and mammals were present at different times in the past. We are using fossils from the Project 23 deposits for this. We have two types of data: mammals (small and larger mammal bones) and plants (plant macrofossils and pollen). For the mammals and plant macrofossils, staff and volunteers at La Brea remove the fossils from the deposits and clean off the asphalt. Researchers at UC Merced and U. Maine then identify which species are present in each deposit. Chunks of intact, asphalt-rich soil is sent to U. Maine so that the fossil pollen can be extracted and identified.


All of the Project 23 boxes, in the park at the La Brea Tar Pits and Museum. Each box, such as the one for Deposit 15, contains part or all of an ancient asphalt seep. And the ancient asphalt often preserves lots and lots of bones.

Once we know which species are present, we will use what we know about modern-day species interactions to reconstruct the food web at La Brea. We’re especially interested in feeding relationships, so the shapes and sizes of animals’ skulls, teeth, and skeletons provide important clues to their diets. We will use knowledge of modern ecosystems and animals to ‘train’ a computer model to predict diet based on animal bodies. Because the animals at La Brea have similar sizes and shapes compared to modern animals (e.g., modern tigers provide clues about sabertooth cats), these models will then provide information about diets. We can also incorporate other types of information such as the abundance of different foods found in the same fossil deposits. We will do this for multiple periods in the last 50,000 years, so we can understand what the ecosystem looked like as the climates changed.

Finally, once we have a picture of the different food webs, we play with them! First, we can look at how the webs actually changed through time, and in different climates or with different set of species present. We can also remove one or a group of species, and see how that affects the overall stability of the system. What happens to a food web if you take out all the mice, for example? These ‘games’ are fun to explore, but also give us some very important information about ecosytems. For example, swapping species in an out of our models can shed light on the role each species plays in the La Brea ecosystem. This can help us answer questions such as ‘are certain types of species more important than others in contributing to the resilience of La Brea ecosystems to climate change?’, or ‘Are certain species more likely to go extinct than others?’ These questions about the past are ones that we can potentially answer, because the fossils tell us how La Brea’s ecosystems have changed through time. Learning about the past can help us to gain a better understanding of the ecosystems in which we live today. 


Contact a member of our team! Or better yet, go visit the La Brea Tar Pits and Museum

the next time you’re in Los Angeles!

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