GEOL388
6-9-04

The terrestrial community



John Merck

Energy flow: Yesterday we neglected a major ecological topic - the flow of energy within an ecosystem. To address this, we need to consider more than just plants, although they are an essential component for it is they who capture the energy of sunlight, by means of photosynthesis, and make it available to other organisms. We think of energy flow in terms of:

For the purposes of our presentation, the terrestrial commnity consists of land plants and all of the critters that get their energy from them. Thus, for this presentation, creatures like sea birds and marine iguanas don't count, even though they often hang out on land. Emphasizing this disconnect is the fact that climatic episodes like El Niño effect the marine and land realms differently.

El Niño spells starvation for sea creatures and happy time for land animals Jackson organizs the major members of the terrestrial ecosystem into a food web. Below is my embellished version:

A couple of comments:

A brief orientation to the more familiar land animals:

Primary consumers

Insects: As anywhere, there is a great diversity, but not so many that a person can't keep track of the important ones. Many of the conspicuous herbivorous insects are nectar-feeding pollinators:

Reptiles: We have two lizards and the tortoise:

Birds: The seed eating and folivorous members of Darwin's finches play the primary consumer part. Without belaboring the issue, the finches we will most often encounter are:

Secondary consumers

Insects: Yeah, predatory insects. A couple worth noting:

Arachnids:

Centipede: The Galápagos centipede, Scolopendra galapagensis is interesting in that it occupies a position in the Galápagos food web analogous to that of a small mammalian predator on the mainland. Indeed, the Galápagos are odd in that the near absence of native mammals has enabled unlikely criters to step into their place.

Insectivorous birds: This encompasses a wide range of endemic, native, and exotic species. Of particular note:

Higher-order consumers

Mockingbirds: When Darwin visited the islands, these were the birds whose island-to-island variation most struck him. Like the North American mockingbird, these creatures are surprisingly bright ecological generalists. They are also capable of hunting young lava lizards, centipedes, and nestling land birds, as well as insects. They are likely to investigate us and, if they are desparate, beg for food or water from us. Their species distribution mirrors that of the lava lizards, with one species each for the old islands, Española and San Cristóbal, and one for the central and western isles:

  • Galápagos snakes: Never seen one of these. Sure would like to. There are three very similar species in two genera. Alsophis slevini and Alsophis dorsalis are spread throughout the central and wester isles while the older islands of Española, San Cristóbal, and Floreana are inhabited by Philodryas biserialis. All species are brown with dull yellow stripes, feed on small reptiles, and are mildly venomous. Like the finches, these snakes are next to impossible to identify in the field.

    Top of the food chain: The ultimate consumers are birds of prey, foremost, the hawk