WK12: Geographic or Global Ecology - Part 1

Emerged from natural history observations.
Early origins linked to natural historians of the late 1700s and 1800s:
- Joseph Banks (Australia).
- Von Humboldt and Von Plante (South America).
- Charles Darwin (South America and Australia).
- Alfred Russell Wallace (Indonesia).
Wallace's Line: A biogeographic boundary distinguishing between Asian and Australian fauna in the Indonesian archipelago.
- North and west: predominantly Asian fauna.
- South and east: predominantly Austro-Papuan fauna.
- The underlying land areas in the Pleistocene were more connected due to lower sea levels.
- Land bridges facilitated fauna movement. For example, Borneo, Sumatra, and Java were linked to Southeast Asia, and Papua New Guinea was linked to Australia via the Sahul Shelf.
- The deep water straight now known as Wallace's Line acted as a barrier, preventing fauna exchange between Southeast Asia and the Austro-Papuan region.

Possibly the most consistent generalization in ecology.
Species richness varies with the total area available.
- Applies to continents, islands, remnant habitats, and aquatic systems like lakes.
- Positive relationship between land area and the number of mammal species (log scales).

Number of mammal species vs. area of continents and large islands.
Number of plant species vs. area of islands in the Galapagos (log scale).
Jim Brown's study using mountain peaks as habitat patches:
- Mountain peaks treated as islands due to isolation by intervening valleys.
- Positive relationship found between land area and the number of mammal species on mountain peaks (log scale).

$S = cA^z$
- S = species richness.
- A = area.
- c = constant.
- z = constant (slope of the line when the equation is logged).
Solving the equation by logging:
- $log(S) = log(c) + z * log(A)$
A plot of species richness vs. log area yields a straight line.
The slope of the line (z) measures how quickly richness increases with area.
If $z = 0.3$ , species richness doubles for every tenfold increase in area.

Jim Brown's work on mountain peaks:
- Compared birds and mammals.
- Found a steeper slope (higher z value) for mammals (0.326) than for birds (0.165).
- Explanation: Birds' higher mobility allows them to move between mountain peaks more easily, reducing the influence of isolation on species richness changes.

Developed by MacArthur and Wilson.
Species richness on islands is determined by an equilibrium between colonization and local extinction events.
Colonization: Arrival and persistence of a species on an island.
Extinction: Loss of a species from a single patch or island (not necessarily global extinction).

Number of species present (x-axis) vs. rate of immigration or extinction (y-axis).
Immigration rate decreases as the number of species increases.
Extinction rate increases as the number of species increases.
The intersection of the immigration and extinction curves indicates the equilibrium number of species.

Distance and area affect the equilibrium species richness.
Empirical evidence from bird colonization of satellite islands around New Guinea:
- Species-area relationship observed.
- Distance effect: Colonization curve is shifted upwards for near islands due to higher dispersal ability.
- Extinction curve is shifted upwards for smaller islands due to increased susceptibility to stochastic events and less area to support species.

The theory postulates a dynamic equilibrium, not a static response.
Species richness fluctuates around a mean due to ongoing species colonizations and extinctions.

Jared Diamond's work on Californian islands:
- Compared species lists of birds from 50 years prior to his study.
- Found that species richness was broadly the same, but species composition had changed.
- Evidence of species extinctions and colonizations occurred, demonstrating a dynamic interaction.