Jumping in Dutch Red Dirt   2 comments


Philip Davison Nature Diaries. Bosque del Cabo Rain Forest Lodge.

The days are now consistently sunny, hot and dry.  Changes are happening in the observable flora and fauna.  Butterfly numbers are increasing in terms of both the number of species and the number of individuals.  But the numbers are still very much lower than would be expected for this time of year.  It could well be that the extended and intense rains of November resulted in the death of many larvae and pupae.  It may take time for those numbers to recover, especially considering the continuing decline seen over the recent two decades.

This time of year is usually noteworthy for the trees and other rain forest plants coming into flower.  There is some visual evidence of several trees coming into bloom but once again not in the number or variety associated with the onset of the dry season.

One other creature notable by its absence at the moment are the cicadas.  January is regarded as the start of a three month period when, during the day at least, your eyes are subject to a continual sonic bombardment of an indescribable intensity.  The larval stage of the cicada is spent below the ground where they feed on sap from plant roots.  It is not beyond the bounds of possibility that many of the larvae were drowned thereby reducing the number of emerging adults which are generally to found in millions this time of year.  For many people that aural attack will not be missed but the ramifications on the ecosystem may have long lasting effects.

Red Alert

One feature of the transition from the wet into the dry season that is very evident as you walk through the forest at this time of year is the production of new leaf.  The feature that makes the new leaf so obvious is the color – red.  Cabo Matapalo is on the South West tip of the Osa Peninsula, Costa Rica.  The location is only 8⁰ North of the Equator.  Any sunlight hitting the earth’s surface at this latitude is therefore intense sunlight and significantly high in ultra violet radiation.  Ultra violet radiation damages developing tissue.  The plants produce a red pigment called anthocyanin which is deposited over the developing chloroplasts and protects them from irradiation.

Anthocyanin

Red is the Color of New Leaf in the Rain Forest

As the chloroplasts mature the plant reabsorbs the anthocyanin and now lays it down as a layer on the bottom of the leaf surface.  Light hitting the forest floor is only 1% of that hitting the canopy so light is of a premium.  Light hitting the leaf will pass through and be bounced off the underlying red layer and reflected back up through the leaf surface so that any light required by the plant to carry out photosynthesis it missed on the way down it will pick up on the way back through.

Many of the young leaves hang droopily facing down.  Those that have no anthocyanin and not having developed much chlorophyll, look pale and ghostly in the in the gloom beneath the canopy.  At this point they are flaccid and not until water is absorbed by the cells do they become turgid and assume their horizontal light gathering aspect.

Fatima Fiesta

One of the butterflies that exhibits very profound seasonal fluctuations is the White Banded Fatima, (Anartia fatima).  It is one of the commonest Costa Rica butterflies.  It is hard to miss with the white bands on the wings contrasting starkly with the dark brown ground color as it flies in open sunny areas such as gardens and disturbed ground.  It can be seen visiting a wide variety of nectar plants.

Whtie-banded Fatima. Nymphalidae. Nymphalinae

White-banded Fatima, (Anartia fatima)

White-banded Fatimas can be found throughout the year in greater or lesser numbers.  This week the numbers started to increase very rapidly.  In some locations there were dozens of them, all looking fresh and new.  But once they reach a peak in numbers and the short-lived reproductive frenzy is over then it will not take long for them to start to take on a tattier appearance and finally within a couple of weeks they will have more or less all gone again.  But later in the year the cycle will repeat.

Dirty Frogs

As the dry season progresses then the creatures that live on the forest floor take shelter in the moister damp conditions beneath the leaves that litter the ground during the heat of the day.  As you walk on the trails and your feet disturb those leaves that disturbance will flush the smaller creatures from their hiding places.  You will see displaced skinks, beetles and frogs seeking safe refuge from your footfall and the sunlight.

Rough-skinned Dirt Frog. Anura. Craugastoridae

Rough-skinned Dirt Frog, (Craugastor rugosus)

There are several small frogs that inhabit the forest floor.  These are the rain frogs mostly in the genus: Craugastoridae.  On the forest trails there are two species in particular that you may come across, the Rough-skinned Dirt Frog, (Craugastor rugosus), and Stejneger’s Dirt Frog, (Craugastor stejnegerianus).  The Rough-skinned Dirt Frog, as the name suggests, has a skin covered in many protuberances.  Stejneger’s Dirt Frog on the other hand has a smoother skin and a generally darker area behind the eye.

Stejneger's Dirt Frog. Frogs

Stejneger’s Dirt Frog, (Craugastor stejnegerianus)

Both these species have life histories that have allowed them to decrease their dependency on water and become more terrestrial in habit, certainly in respect to reproduction.  Whereas most amphibians must return to the water to breed, the rain frogs pair up and lay their eggs amongst the leaf litter on the forest floor.  The microclimate beneath the leaves is damper than that above which suits both the frogs and their eggs, it stops them from drying up.  Aquatic egg-laying frogs face the problem of having many predators in the water that will feed on the eggs and the tadpoles.  Rain frogs do not face the same intense predation pressure and can therefore produce fewer but larger eggs.  The larger size of the egg allows full development of the tadpole within a protective gelatinous coating.  A larger amount of yolk is provided which supplies enough sustenance for the frog to complete development and emerge four or five weeks later as a tiny copy of the adult.

Craugastor stejnegerianus. Amphibia.

Stejneger’s Dirt Frog – One too many flashes and It’s Away.

Jumping in Color

Moments after photographing Stejnegers’ Dirt Frog I noticed a tiny black speck of a leaf which moved in a very distinctive and familiar fashion.  The almost indiscernible black dot was a jumping spider.  It had turned to look at me which is how it gave away its presence.  I had to turn the camera lens on it and take same photographs to truly appreciate the amazing little creature I had in front of me.

Jumping spiders belong to the most diverse spider family: Salticidae of which there are more than 5,000 named species around the world.  In Costa Rica there is not a wealth of reference material you can consult in an effort to make an identification.  Sometimes family level is about as far as you can go.

Jumping Spider. Osa Peninsula.

Unidentified Jumping Spider, (Salticidae).

The most distinctive feature of the jumping spiders is the large anterior forward facing eyes.  These give the spider the ability to see things at close range.  They can be seen orientating themselves to watch you.  That is what this one was doing with me.  Unlike their web-building relatives, the jumping spiders hunt their prey down.  Once they identify a potential meal they will pursue it and at the last moment pounce on it, deliver the venomous bite and consume it.

Their visual abilities allow them to use coloration as a cue in mating.  The males may have brightly colored legs and pedipalps to court the females.  This species had bright blue legs and yellow pedipalps.  When a male sees a female he performs a series a ritual dance moves which include lifting his legs in a certain sequence as well as moving in a series of set maneuvers in front of her.  All the while the female is watching, scrutinizing the performance.  One blunder and she will leave having no further interest.  Each species of jumping spider has a very specific dance routine thereby negating the change of courting the wrong type of girl.

Salticidae. Spiders.

Unidentified Jumping Spider. Look at Those Eyes.

Dutch Piper

One of the most distinctive flowers of the forest understory is that of the Aristolochia vines otherwise known as the Dutchman’s Pipe Vine.  As with most flowers the sole purpose is the achieve reproduction through pollination.  Many plants have evolved ingenious means by which to use the flowers as a means to this end.  The Dutchman’s Pipe is one of them.

The flowers are named after their resemble to the carved tobacco smoking pipes used in Holland.  But to a carrion fly they look somewhat different.  Carrion flies are attracted to the fetid odor of rotting flesh.  The flowers of this species of Dutchman’s Pipe, (Aristolochia gaudotii).   give off a scent which mimics the stench of a putrefying body.  The pale yellow base color reticulated with maroon blotches visually emphasize the illusion.

Dutchman's Pipe. Aristolochiaceae.

Dutchman’s Pipe, (Aristolochia gaudotii)

The flies land but find themselves incapable of maintaining a footing on the slippery oily inner surface of the flower and slip down into the interior.  They are unable to make an immediate escape as their exit is blocked by a barrage of downward pointing stiff hairs.  They are trapped.  During the period of vegetative incarceration, the fly struggles violently in order to gain its freedom.  This results in the body becoming covered in pollen.  The following day the stiff hairs wither and the fly finds its exit clear only to fly off and respond to the same trickery.  This time it transfers the pollen thereby pollinating the flower after which it will be released from its temporary floral prison with a fresh coating of pollen.

Aristolochia gaudotii. Carrion Fly.

Dutchman’s Pipe. Looking Down Through the Prison Bars.

Philip Davison is a Biologist, Writer and Photographer Based in Costa Rica

 

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2 responses to “Jumping in Dutch Red Dirt

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  1. Fun read, especially since we never visit this time of year. You’d be proud of me, Phillip. I waylaid Fred from placing a giant house spider from our living room out in the 32 degree weather and suggested he put it in the garage. Most of the time I can ignore them, where in the past I would vacate the house until someone killed it. I’ve learned through you and others to never kill spiders, esp. non-poisonous ones. Baby steps.

    Like

  2. Ugh. I misspelled your first name. Bad Jen.

    Like

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