Si-Chong Chen (@SichongChen), Wuhan Botanical Garden of the Chinese Academy of Sciences, discusses her article: Large seeds as a defensive strategy against partial granivory in the Fagaceae
Imagine you are an acorn. You’re packed with nutrients and a perfect meal for animals like squirrels and birds. But you’re not just food; you’re also a seed with the mission to grow into a mighty oak. How do you survive being eaten? Our recent research offers fascinating insights into how big seeds like acorns balance the risks and rewards of their size.
The Challenge of Being Large and Nutritious
Large seeds, such as those from oak trees, pack a lot of resources to kickstart their growth, but this also makes them a target for animals that see them as a convenient snack. In a unique twist, animals that eat seeds can also help disperse them. This dual role – as both predator and disperser – is a key feature of a seed dispersal strategy called synzoochory. Scatter-hoarding animals like squirrels often bury seeds and forget about them, giving the seeds a chance to germinate and grow in new locations.
But what happens when animals eat part of the seed? Does losing some of their nutrient reserves hurt the seed’s chances of survival?
A Closer Look at Partial Predation
Our latest study tested this question using acorns from 20 species in the oak and beech family (Fagaceae). We simulated what happens when seeds lose parts of their nutrient reserves due to animal feeding by carefully cutting away up to 96% of the acorns’ reserves without damaging the embryo. These seeds were then planted and their progress was tracked from germination to seedling growth.
Resilience Against the Odds
The results were surprising. Despite losing a significant portion of their reserves, most seeds still managed to germinate. This suggests that seeds are equipped with more nutrients than just what they need for germination – a built-in buffer against partial consumption.
However, while germination was not greatly affected, seedling growth was another story. Seedlings from heavily damaged seeds were smaller and had fewer leaves and less total biomass. To make up for their limited resources, these seedlings grew thinner leaves, maximising surface area for photosynthesis. It is a clever strategy but comes with a trade-off: thinner leaves are more vulnerable to herbivores.
Why Are Big Seeds So Successful?
Our study suggests that large seeds have evolved their size not just to provide extra resources for the growing seedling but also as a defence mechanism. By tolerating partial predation, these seeds can survive and germinate while still benefiting from being dispersed by animals. Interestingly, the larger the seed, the more likely it is to survive partial consumption. This makes large seed size an effective adaptation for balancing the competing demands of dispersal and predation.
Implications for Conservation and Forestry
Our findings could have practical applications. For instance, seeds that are partially damaged but still viable could be used in reforestation projects, particularly during years when seed supplies are low. Understanding how different species cope with partial predation can also guide conservation efforts for forests and other ecosystems.
The Big Picture
This research sheds light on why plants invest so much energy into producing large seeds. It turns out that being big isn’t just about growth potential – it’s also about resilience and survival. Large seeds like acorns are a remarkable example of how plants adapt to their environment, working with – and sometimes against – the animals around them to ensure their success.
So the next time you see an acorn, take a moment to appreciate its clever design. It’s more than just a snack for squirrels; it’s a testament to the intricate strategies of nature.
