Good Things Come in Small Packages
Enhanced Video Resource

The island of Cuba is home to many diverse and unique species.  This video from NATURE introduces the smallest bird in the world, the smallest frog in the Northern hemisphere, and the country’s famous painted snails.  The video explores how these distinctive animals interact with Cuba’s wildlife and ecosystems.

Discussion Questions:

  • Observe and note the different ecosystems present on the island of Cuba.  How do all of these different ecosystems function together on the relatively small island?
  • How do you think the bee hummingbird finds enough food to consume up to half of its body weight each day?
  • What do you think the advantages and disadvantages might be of the polymitas brightly colored shells?  Explain.
  • Why do you think Cuba is home to so many of the smallest animals in the world?

Background Essay:

Cuba’s wildlife is varied and unlike wildlife anywhere else in the world.  This is no coincidence – the island, while close to its North and South American neighbors, has been evolving in isolation for thousands of years.  Extraordinary things tend to happen to species evolving in isolation; the unique combination of predators and competition for resources – or, often times, the lack thereof – allows species to adapt in ways they never would on the mainland.  Species adopt new characteristics, behaviors, or patterns that distinguish them from their mainland counterparts.

In some cases, island species move in the direction of gigantism, as the lack of competition and predators allows them to use all available resources and grow as large as possible.  In other cases, such as in Cuba, species will tend toward dwarfism, becoming smaller and conserving resources.  Dwarfism has its advantages, as it enables organisms to absorb nutrients and energy more efficiently, hide from predators more easily, and ably cope with stressful environmental conditions.  This drastic evolutionary size change in species is known as Foster’s rule, or the island rule (as the phenomenon is a core principle of island biogeography).  Furthermore, the size change in species can happen very quickly on islands, much more quickly than evolutionary changes in mainland species.  Mutations and adaptions spread through generations rapidly since there is a much smaller gene pool in the isolated island environment.

Thanks to the special evolution that has taken place on Cuba, the island is now home to some of the smallest and most interesting species on Earth.  The bee hummingbird, known locally as the zuzuncito, is the smallest bird in the world – named because it is no bigger than a honeybee!  This tiny bird is often mistaken for an insect, and is thus prey for larger birds, frogs, fish, and tropical spiders.  Cuba is also home to the second smallest frog in the world, the Mount Iberia Eleuth.  This miniscule frog, only half the size of a dime, lives in two relatively small regions of the country and requires a great deal of humidity to survive.  Other dwarfed species endemic to Cuba include the world’s smallest scorpion, one of the world’s smallest owls, and extremely small varieties of bats.

The unusual evolutionary trends of Cuba extend not only to dwarfed species, but to animals with other unique characteristics.  Perhaps the greatest example of this are the polymitas, or Cuba’s painted snails.  These snails are known for their vibrantly colored shells, which come in a variety of dazzling hues and, of course, are found nowhere else in the world.

Unfortunately, several of Cuba’s distinctive endemic species are becoming or are already threatened.  This is due to a variety of factors, many of them caused by human activity: habitat loss, deforestation, agricultural development and mining, and tourism.  The polymitas are also “hunted” for their shells, popular as jewelry and as collectors’ items, which seriously threatens their populations.  As Cuba continues to open its doors to the world, its great diversity of plant, reptile, bird, and mammal species will be further threatened by human interference.

National Science Education Standards:

Life Science

Content Standard C

BIOLOGICAL EVOLUTION

[See Unifying Concepts and Processes]

  • Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuring selection by the environment of those offspring better able to survive and leave offspring.

The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.

THE INTERDEPENDENCE OF ORGANISMS

Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.

Human beings live within the world’s ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and if not addressed, ecosystems will be irreversibly affected.

Tags: , , ,

Inside This Lesson

Produced by THIRTEEN    ©2014 Educational Broadcasting Corporation. All rights reserved.

PBS is a 501(c)(3) not-for-profit organization.