Allanblackia: my hypotheses

A few weeks ago, I shared some background information about a project I am working on with the Allanblackia tree species and invited you to make your own hypotheses about how seed dispersal and the tree population might change over time if there are fewer seeds in the forest.

I have two main hypotheses about what will happen to seed dispersal:

1) Allanblackia seeds will be carried further by rodents if there are fewer seeds.

2) Seeds moved by rodents are more likely to get eaten before they are able to germinate.

I think the seeds will be moved further because the rodents want to reduce the risk of other rodents finding "their" seeds and eating them. If there are lots of seeds around, then they can be a bit lazy and just hide them nearby. If there aren't many seeds though, they carry them farther away so other rodents going to the source are less likely to find them.

Any individual seed has a chance of getting eaten or being forgotten by a rodent. If it's forgotten, then the seed might germinate and sprout into a seedling. I think that if there are fewer seeds around, the chance of any one seed getting eaten is much higher. The rats have to eat!

In order to test my hypotheses, I'm putting groups of 16 seeds in different places in the forest, but I need to come up with a way to:

1) Find where the seeds are being moved and how far they are going

2) Revisit the seed over several weeks or months to see if it germinates.

What would you do? How would you track these seeds in the forest? They are roughly the size of a walnut. How would you know if the seed you find is one from the experiment?

Soon I'll let you know how I'm tracking the seeds, but I would love to hear your ideas!

Mystery photo #3 revealed

The last mystery photo was a close up of a caterpillar covered in parasitoid wasp cocoons! Here's the full size photo.

This is one caterpillar that won't ever be a butterfly (or moth). Why not? And what is a parasitoid wasp? The adult female wasps search for particular species of caterpillars and deposit the eggs inside the caterpillars' body. Then the wasp live inside the caterpillar and slowly eat it from the inside out. When the little buggers are finished, they make cocoons on the caterpillars' back and pupate. Then the next generation of wasps will emerge from the cocoons on the back! The caterpillar will die before it is able to pupate, and so it will never reach adulthood or reproduce.

Some insects like parasitoid wasps can be very beneficial for farmers if they lay eggs on caterpillar species that damage crops. You don't have to go to Africa to see parasitoid wasps! You can find them if you grow tomatoes in Chicago! Large, green caterpillars called tomato hornworms eat tomato plants, but also have their own parasitoid wasp species. The cocoons are very similar to these and will appear on the parasitized caterpillars (from a distance they look like they would be white oblong eggs, but if you look closely you can see the little threads of the cocoon).

One of the reasons I love studying biology is because I get to learn about fascinating relationships between different organisms. Would you ever have guessed that some wasps grow up inside a caterpillar!?

Mystery photo #3

This week's photo has nothing to do with seeds! There are two different animals in this photo. Can you describe them? Do you know what they are?

If I see something interesting in the forest, I try to take a photo and write a note about it even if it isn't directly related to my research, which is the case with this photo. Maybe my observation will help someone else with their research!

Mystery photo #2 revealed

Last week's mystery photo was a picture of a giant pouched rat. These large rats have cheek pouches like hamsters, which distinguishes them from many other rats (including the rats that are common in cities). The rat in the photo has really stuffed his cheeks full of seeds! Then they hide the seeds somewhere else in the forest (like squirrels with acorns) or bring it back to their burrow.

Here is another photo of a giant rat with his cheek pouches empty. He looks a bit more rat-like in this pose.

These rats are hunted and eaten in many places in Africa, but some people in the U.S. and Europe keep this species as pets. Unfortunately, some have escaped in Florida and they are now an invasive species. But here in Tanzania, they play an important role as seed dispersers.