LARGE-SCALE ECOLOGY UNIT
Chapter 21: Landscape Ecology:
Landscape Structure
Patch Size and Fragmentation of habitat
Examples:
Six landscapes in Ohio (pgs. 447- 450) – comparison of forested versus deforested
habitat
Important concepts: individual patch size; patch shape; proximity of
other patches
Ecotones and the edge effect
Patch Size
and the Glanville Fritillary (Melitaea
cinxia) in Finland (pgs. 452-453)
Increasing patch size increases numbers of butterflies on the patch, but
the density decreases
The
decreasing density is NOT a general trend for all species in relation to patch
size
(see just below)
Habitat Corridors – connectors between patches; natural or manmade
corridors (a management practice
that is
used to connect patches, and effectively make for larger patches) (pgs. 453-454)
Example: the Buckeye Butterfly (Junonia
coenia) and Variegated Fritillary (Euptoieta
claudia)
in
South Carolina. Corridors cut in
pine forest connected patches, resulting in higher densities
for
both butterflies in such open habitats connected by corridors
Further
studies in the same area indicated higher rates of pollination and higher rates
of seed
dispersal (by birds) of plants growing in these connected patches
The discussion of Patches is a perfect lead in to discuss island biogeography in
chapter 22
Chapter
22: Geographic Ecology
Area, Isolation, and Species Richness:
Island Biogeography (pgs. 470-475; and our last lab)
Remember
that islands can be land surrounded by water, but also separate lakes in a
landscape
separate mountaintops in
chain, etc.
Important
concepts: Area (size) of the
island, proximity of the island to source areas (for
immigrants), age of the island, including whether the island was
connected in the past to the
source area or other islands.
The discussion could also include the age of the group of
organisms from an evolutionary standpoint, which effects how long the group of
organisms has
had to colonize various islands (see Azore Islands data, Fig. 22.6, bottom of
pg. 472).
Examples:
Area -- birds on Caribbean Islands, ground beetles (carabids) on islands
in a Swedish lake,
mammals on mountains in the American SW, fish in lakes in northern
Wisconsin
Distance from mainland – bird species richness on islands at various
distances from the large island of
New Guinea; and again mammal species on mountains in the American SW
(Fig. 22.7, pg. 473)
The Equilibrium Model – with Immigration/Extinction curves; predictive value for
indicating total number
of species an island can have based on area and proximity to source area (Fig.
22.8, pg. 474)
Latitudinal (and Altitudinal) Gradients in Species Richness:
See pages 478-480
For
overall richness of communities, there is no question that the most diverse
terrestrial
communities are tropical rainforests, and coral reefs for aquatic.
There is a general trend of decreasing
species richness as you move away from the equator either toward the south or
the north. This trend is
apparent in specific groups of species as well, such as several plant groups,
birds, etc. But this trend is
NOT true for all species groups.
Examples include salamanders (richer in the temperate zone and highest
in diversity in our own Great Smokey Mountain Nat’l Park), and ichneumonid
wasps, also with the highest
diversity in temperate zones. Can
you think of others??