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Lecture 3

BIO120H1 Lecture Notes - Lecture 3: Daniel H. Janzen, Temperate Climate, Her Majesty'S Ship

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Spencer Barrett

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Lecture 3 What Darwin Saw on the Beagle; A Geographical Perspective on
Biodiversity and Adaptation
1. Contrasts between tropical & temperate ecosystems
2. The role of biotic and abiotic interactions in temperate and tropical ecosystems,
3. Galapagos islands as evolutionary laboratories
4. Australia’s isolation and its unique biota
Charles Darwin’s Voyage on H.M.S. Beagle (1831-1836)
- Age 22, ships naturalist (collects life)
- Most time spent in South America
- Observations of fossils, geographical distribution of plants and animals, and flora and
fauna of oceanic islands
H.M.S. Beagle sails to Brazil (tropical forests in Brazil):
- Very high species diversity of plant and animal groups compared with temperate zone
- Many more biotic interactions, especially coevolved mutualisms between plants and
- Year-round warmth results in rapid growth of insect and microbial populations. Pest and
disease pressures on plants are more intense
- Creates a greater chance for natural selection
Problem with Diversity:
- Species become isolated and unable to reproduce and survive (too many different
- E.g. trees (animals now help trees as the dominate form of pollination)
Tropical trees are largely animal-pollinated whereas temperate trees are mostly wind pollinated:
- Tropical forests have high species diversity and individuals of the same species are
widely separated; unlike temperate forests
- Tropical forests are also largely evergreen (non-deciduous) unlike most temperate forests
- Dense canopies and long-distances between trees make wind a poor agent of pollen
dispersal; animals are more effective pollinators
- Bees, butterflies, moths, birds, and bats pollinate most tropical trees; most temperate tree
wind pollinated
Euglossine Bees as long-distance pollinators of tropical plants
- Daniel Janzen (1971) used mark-recapture techniques to demonstrate that bees travel up
to 23 km during a day
- Today widely recognized that bees, moths, and hummingbirds travel long distances
during “trapline” (following a specific path) foraging
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