Evolutionary trade-offs: You cannot have it all!

 

Can you think of an organism that starts producing babies immediately after it is born, produces an unlimited number of them during its life and also lives forever? Here is the reason why you cannot: life history trade-offs! These explain why animals and plants vary so much in how quickly they grow up, how many babies they have and how long they live.

Choose your animal, choose how you will invest your energy and play a game to find out how successful you can be! Will you and your babies survive long enough to win?

tradeoffs


Swedish summary:

Kan du komma på en organism som börjar få avkommor direkt efter att den fötts, få ett obegränsat antal avkommor under sitt liv och dessutom lever för alltid? Anledningen till att du inte kan komma på någon sådan organism beror på olika avvägningar organismer har tvingats göra i deras livshistoria. Dessa avvägningar förklarar varför djur och växter varierar så mycket i hur snabbt de växer, hur många avkommor de kan få och hur länge de lever.

Välj ditt djur, välj sedan hur du vill investera din energi och spela ett spel för att se hur framgångsrik du kan bli! Kommer du och dina avkommor att överleva länge nog för att vinna spelet?


 

Introduction

Even in evolutionary biology you cannot have it all! Can you think of an organism that starts producing babies immediately after it is born, produces an unlimited number of them during its life and also lives forever? Obviously, nobody has ever seen such an organism – it does not exist. Instead, what we see in nature is a wide diversity of “lifestyles” or, in other words, life histories. Some organisms have very short lives, yet produce a huge number of offspring (i.e. babies), like beetles, fishes, mice and rabbits. On the other hand, some other organisms, like humans and elephants, produce a limited number of offspring and live long lives. Why do we see such diverse patterns and how did they evolve? Why a strategy that is good for one organism is not optimal for another one? The answer lies in life-history trade-offs. Come here to find out what they are and why they matter!

 

The activity

We want to have two main activities: one suitable for younger children (and up!) and another one for older children and adults. These activities build on each other, so if some visitors are interested, they can go further into the topic, or stay only at the beginning

Activity 1: We want to demonstrate that allocation of resources underlies trade-offs among competing traits (here we will focus on reproduction and it will be a trade-off between quality or quantity of one’s offspring), and link different strategies that emerge from such trade-off to environmental selective pressures acting on organisms.

We will be using clay or play dough and large and small moulds so that the participants can build up same objects of different sizes. Participants can choose to divide their clay/play dough into either few big blobs or numerous small blobs. Blobs represent offspring. After making these blobs a participant draws a card/rolls a dice that says that either a big predator came and ate some of your offspring or there was no food so your offspring starved. The idea is that big predators play on big offspring and thus select for numerous small offspring strategy (because in such case at least some of your offspring should avoid the predator and survive) while starvation selects for fewer big offspring as bigger offspring have more resources and are more likely to survive starvation.

Activity 2: Board game with a dice. This activity demonstrates a few important ideas:

  1. the differences between individuals in acquisition of resources/quality
  2. the trade-off between lifespan/somatic maintenance and reproduction,
  3. the trade-off between early and late-life reproduction,
  4. the concept of fitness, and
  5. the role of random events in determining your fitness.

First round: In the beginning each participant rolls a dice to decide how many life points = resources s/he will have (quality differences between individuals).
Second round: Reproduction, the number you get by rolling a dice = number of offspring you produced which is subtracted from your life points (a trade-off between reproduction and lifespan, here one offspring is always worth 1 point).
Third round: How many of your offspring got eaten and didn’t survive? You subtract the number you get from the number of offspring alive. (Random events affecting surviving offspring)
Fourth round: The world of unpredictable events – winter can be harsh or a predator can chase you. The number that you get by rolling a dice is subtracted from your life points. No points – the game is over. (Random events affecting your survival and thereby your chances of reproducing during the next round)
Fifth round: Reproduction again (subtract from life points). (If you reproduced early you have fewer points to reproduce now – early-late reproduction trade-off)
Sixth round: Progeny eaten (subtract from the number of offspring).
Seventh round: Unpredictable events (subtract from life points) and so on until the last participant has no points. Participants have to keep track of their life points as well as the number of offspring alive (We will think further on how to keep track of that in a fun interactive way). At the end the participant with the highest number of offspring alive wins (fitness!).

Bonus activities:

  1. A general Poster of the topic we have introduced with the activities and one or two more posters with additional topics (e.g. sex-differences in life history trade-offs and strategies) that can guide discussions with adults who want to know more
  2. We will bring examples from nature for the visitors to see (unless if we can borrow or use things from the museum). For example in the first activity (quality Vs quantity of offspring) we were thinking of bringing avocado seeds and vanilla seeds etc.
  3. Videos and parts of documentaries for more example of species with different life history strategies (we will have to make sure abour the copywrite licencies though)

 

Members

 

Resources of interest

 

 

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