Thursday, 13 February 2014

Costa Rica: Reflections

In the primary rain forest

We had a holiday in Costa Rica in January and I described some of the things we did in posts about La Paz Waterfall Garden, Selva Verde, Arenal Volcano and Selvatura. Here I want to reflect on what we learned from the experience and what impact it had on us.

Costa Rica is a small country. Its population is 4.5 million and it covers an area of 20,000 square miles - compare England with its 53 million population (the population of the whole UK is 63 million, both figures from the 2011 Census) and 50,000 square mile area.

We were intrigued to learn that the country is officially neutral and abolished its armed forces in 1948, using the money to provide comprehensive education and health systems. (Certain armed forces functions reside in the Police however.)  This is evidence of the visionary leadership which seems to be something of a national characteristic.

Tourism is the number one industry and Costa Rica is well known as a destination for eco tourism. After a long period of deforestation, the first national park was set up in 1963 and there are now over 190 national parks, biological reserves, wildlife refuges and similar entities. This means that an incredible 30% of the land is now protected.

 Scarlet macaws

We learned that the next big step in nature conservation is now being taken: the creation of biological corridors on a national scale linking together the numerous separate parks and reserves. This is very impressive. The Making Space for Nature report for DEFRA (the Lawton report) concluded in 2010 that "the essence of what needs to be done to enhance the resilience and coherence of England’s ecological network can be summarised in four words: more, bigger, better and joined." But unlike in Costa Rica, nothing much has yet happened.

Costa Rica can claim to be home to almost 5% of the identified living species on the plant. Our tour guides were all very proud of the number of species of butterflies, birds etc - even if the numbers quoted were a bit variable. (They were also notably well-informed and passionate about their subject, and proud of their country.) To take a single example, there are generally accepted to be about 18, 000 species of butterfly in the world and Costa Rica has 1600-2000 of them. This is more species than are found in the USA or the whole of Africa.

 A white-faced monkey

There seem to be two main reasons for this incredible richness of wildlife. Firstly, there is its geological history. About 3 million years ago the evolution of the earth's land mass had reached a point where north and south America were separate land masses with a gap between them. At that point, a movement of tectonic plates pushed up the land bridge that now exists as Nicaragua, Costa Rica and Panama. Plants and wildlife have been dispersing across that bridge from north and south ever since. And bird migrations continue in both directions.

Secondly, the country contains a wide range of different habitats: lowland rainforest and montane cloud forest on both sides of the central chain of mountain, montane and sub-alpine zones at higher altitudes, tropical dry forest in the north, wetlands and coastal zones.

 Roseate Spoonbills and other wetland birds

We found however that it was surprisingly difficult to see butterflies in the wild and we spent some time wondering why this was. It became fairly clear that there are not a lot of wild flowers in most of the habitats we visited and we read that gardens, rather than the wild, were often good places to see butterflies. Secondly, we learned that the very best time for butterflies was in the rainy season when many of them breed. We went in the more popular (with tourists anyway) dry season. This is in fact only truly dry in the north, the Guanacaste region; elsewhere it rains all year round and is simply a bit less wet at this time of year.

But probably the main reason was that the diversity of wildlife already noted means that there are a great variety of predators for butterflies at each stage of their life cycle. So there are plenty of species, but not many of each of one. And finally, many are only found in specialised habitats or times of year, so you would never be able to see all species in a short period of time spent in a few places. Now we understood something that had puzzled us when we were planning our trip: why were there so many butterfly houses? I had in a rather purist way insisted that I didn't want to visit any of them, but it didn't take too long to realised that this would be self-defeating and I succumbed. I am glad I did! At least, unlike butterfly houses in other countries, there were only native species.

A Blue Morpho in the Monteverde butterfly house

Predation of butterflies leads me to a rather banal, but important, overall conclusion. With so many species there is a much more complex hierarchy of predation or food chain. At the top level for example, there are the big cats, jaguars, cougars and pumas.  Nature has a much more raw, tooth and claw, fight for survival quality than we are used to in England.

Green poison-dart frog

This in turn leads to a truly incredible array of symbiotic and parasitical relationships, elaborate defence systems based on toxins of various kinds on the one hand and disguise and mimicry on the other.

Here are just a few examples:

Some trees have a symbiotic relationship with species of ant: the tree provides food for the ant, while the ants fight off any other species which tries to attack the tree.

There are a number of brightly coloured poison-dart frogs, including the tiny Blue-jeans frog (bright red with blue legs). This is an example of the aposematism in which markings are indicative of unpalatability. (Incidentally, the poison-dart frog does not in fact shoot poison darts as one might imagine: its secretions were allegedly used by Amerindians to coat the tips of their blow-darts.)

When palm trees are attacked by insects they secrete toxins at the eaten edges of leaves. At least one palm tree has evolved to have leaves which look as though they have been previously attacked.

Finally, consider these two butterflies: the Postman on the left and the False Postman (same colours, different arrangement) on the right.

This is another example of mimicry. The Postman is poisonous and if the False Postman was not it would be an example of Batesian mimicry, where a non-toxic species evolves to take on the look of a toxic one as a means of defence. Alternatively, in Mullerian mimicry, a number of similar species are all poisonous and have evolved a similar colour scheme. This is thought to increase their collective safety by making it easier for predators to learn what not to eat. (To be honest I am not sure which type is being displayed by this pair of butterflies.)

We also learned the answer to one of the great nature questions: what are wasps for? In Costa Rica at least, species of small parasitic wasps have a complex symbiotic relationship with certain fig plants, in which they are central to the plants' ability to reproduce.

In conclusion then, understanding something about these interdependencies and mechanisms was more interesting and enlightening than simply spotting various exotic species and was the real pay-off of our trip. 

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