The Species On The Globe Go Round And Round

Today we associate lions with Africa, but they used to be widespread around the northern hemisphere (Image Credit: MLbay, Pixabay licence, Image Cropped)

While I continuously hear my little one’s nursery rhyme about a certain stuff going round and round, I think, what else moves round and round in my field? Species! 

They move around as they are looking for a mate, food, to avoid cold weather, the list goes on. They occupy a reasonable range that can be handled by their bodily functions, and either stay in that range or move when the environment changes. A species’ historical movement is one of the most important aspects of its natural history.

Species Movement Across The Globe

When we look at species on their evolutionary scale, we can see that their ranges change during their evolutionary lifetime. The largest lizard thought to ever have existed was thought to have lived nowhere other than the islands of Nusa Tenggara Timur, Indonesia. Until recently, when it was actually found in Australia… in the form of an Ice Age fossil. Rhinoceroses, I thought, were a group of species only inhabiting Indonesia’s western islands and Africa, but apparently they were quite widespread a million years ago. My ignorant self was surprised to discover there were rhinos in Europe as recently as 40,000 years ago!

There are a lot of animals that were found around the globe for quite some time before becoming associated with a distinct region. Around 500,000 years ago, lions were present in North America and Eurasia, but now they can only be found in Sub-saharan Africa and parts of South Asia. The ratites – the family of birds that the ostrich and emu belong to–were once widespread in Eurasia but now can only be found in the southern hemisphere. 

When species can move to occupy more habitat and get more resources, they will. So what can prevent them from doing so? 

Firstly, their mode of locomotion – elephants can’t fly from island to island, no matter how hard you cling to Dumbo. But even if they can move, certain aspects of an environment might prevent this. And even if the environment is fine, the native species might not let the newcomers gain a foothold. 

But if those three barriers aren’t present, new habitat is always a boost for a species. This is why the ratites have become bigger in certain areas where there are less competitors, and why smaller species tend to become larger when they disperse to islands. It is the natural tendency of species to move and occupy more habitat when resources are available.

How about when humans started to move around?

The Movement Is Even Older

There are various cases where humans have moved biodiversity around the globe. Early humans migrated with livestock as their food, for example, while accidentally bringing other animals that are not their food with them. Later on, exotic animals were sought and transported across the globe for the collections of aristocrats, while voyages also distributed various marine invertebrates as ballast or stowaways. As humans populate more of the world, some areas become more inaccessible to the local critters, and the scarcity of space affects the local population in different aspects.

When we look at our planet’s current biodiversity, we are also looking at the remnants of the activities of our ancestors. In my own home country in Indonesia, for example, many of the dogs, cats, trees, and fruits are recent arrivals to the 60 million year-old islands. Our domestic cats and dogs are likely to be from around Central Asia. Plants, despite being relatively sessile, also change their distribution. Our culinary culture consists of plenty of plant species not initially native to our region.

Gray cuscus (Phalanger orientalis) picture taken near an area in Mount Mutis, Timor Island, called Kasliu (Source: Tropenmuseum, 1937, CC-BY-SA 3.0). It is thought to be naturally distributed in Oceania and the eastern part of Indonesia. Knowing early humans brought them, did they naturally disperse though?

Wilder plant and animal species are also not settling on the islands entirely on their own. There is a hypothesis that the current distribution of our famous gray cuscus (Phalanger orientalis) were a product of early humans migrating around the Pacific islands about 20,000 years ago. We know this from the bone remains in the ancient Pleistocene caves where human remains and animal remains are both found. I trust the paleozoologists and archeologists on this one.

Another amazing story about humans accidentally bringing animals around the globe is about how a certain mollusc (the aptly-named shipworm) attacked past wooden ships. I first read it on a Twitter thread here, but apparently this story is not that new. If you have trypophobia, it is not recommended to look about their habitat further (also why no picture is included in this blog post).

Does this mean moving species around is okay? Can our activities in moving species be considered natural?

Behind The Release 

In a previous post, I mentioned how important it is to evaluate the genetic diversity of a population before you move new individuals to that population. This is important when the goal is to increase the wild population’s chances of survival through increasing their genetic diversity. Also importantly, the individual that will be moved should not be too different from the recipient population in genetic variation or they will risk getting their genetic makeup disrupted. The latter is dangerous when the population has a certain mode of adaptation already embedded in their genes. The arrival of a newcomer not having this advantageous adaptation will just ruin the hard evolutionary work done over thousands of generations.

The idea of saving distinct population genetic diversity is neat, but also problematic when taken to extremes. Many conservation projects that could benefit from the addition of new individuals from a supposedly healthier population usually are against such translocation for the exact reason of preserving local genetic diversity. Such concerns are only justified when the harm well outweighs the benefit, and this needs thorough scientific investigation rather than endless ethical debate. An article about the history of many intended translocations in the U.S. might give you an idea on how much we should worry about moving species around.

We are fortunately increasingly more thoughtful about how and where we  move species. Zoonotic disease monitoring is ongoing, quarantining animals and plants moving across borders is more commonplace nowadays, and a certain pigeon thought to come from another continent makes a headline. I’ll be happy if more people can appreciate that this moving business is as old as life itself, and separating humans from the whole process will mess up the big picture of our interaction with biodiversity. We cannot avoid our relationship with nature in time and space, but we can at least control some aspects as we know more about the impact of some of our activities.

Sabhrina Gita Aninta is a conservation geneticist currently pursuing her PhD at Queen Mary University of London to understand how genome-wide variation of the endemic pigs and buffalos from Southeast Asia could assist their conservation. Follow her Twitter here for an update of her work, along with a mix of conservation, biodiversity, evolution, but mostly various rants and random stuffs in Indonesian and English. You can find more of her work at Ecology for the Masses at her profile.

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