Ornithology Notes: Biogeography and Convergence
Ornithology: 11:216:323 Spring 2025
Mondays and Thursdays 12:10-1:30pm, Foran Hall 138A, Thomas J. Duchak
Biogeography and Convergence
Biogeography
Definition: Where and Why do you find What?
Determinants of Species Distributions
Biogeographic Regions
Cosmopolitanism and Endemism
Determinants of Biodiversity
Convergence
Definition
Full Convergence (Extant Examples)
Niche Convergence (Extant Examples)
Examples Across Time
Group Discussion Questions (GDQ 10)
Think of any type of animal group. A non-bird example is okay. Be specific but don't choose a monotypic group (i.e., a one species group)!
e.g., marsupials - but don't do this one!
Research and describe your group's geographic distribution.
Hypothesize potential reasons for your group's geographic distribution.
Biogeography Defined
Where and Why do you find What?
Determinants of Species Distributions
Where did the species first evolve?
How far can/could the species get (Dispersal Filter)?
Species' mobility?
Any barriers to dispersal?
Are/were natural colonizations possible?
What are/were the species' physiological tolerances (Abiotic Filter)?
In which regions can/could they survive the abiotic conditions? In which regions can/could they not survive?
e.g., Climate, temperature, water, etc.
What other species/populations can/could the species thrive with (Biotic Filter)?
In which regions can/could they survive the biotic conditions? In which regions can/could they not survive?
e.g., Food, competition, predation, disease, etc.
How did history play a role?
Introductions by humans or potentially other species?
Local extinctions?
Earth's geologic history (i.e., Continental Drift and Vicariance)
Continental Drift
Much of Biogeography can be explained by past and present geologic history
Continental Drift = Movements of the continents over time
Continents are islands of low-density rock floating on denser material of Earth's interior; carried along by convection currents
220 MYA Continents United = Pangaea
Permian Period 250 Ma
Cretaceous Period 100 Mya
Early Tertiary Period 60 Mya
Earth Today: Continents Mostly Divided
Fossil Evidence for Continental Drift
Fossil remains of Cynognathus
Transic land reptile approximately 3m long
Fossil remains of the Freshwater reptile, Mesosaurus
Fossils of the fern Glossopteris, found in all of the southern continents, show that they were once joined
Biogeographic Regions
Alfred Russel Wallace: "Father" of Biogeography
Modern distributions of animals led Alfred Russel Wallace to recognize six major Biogeographic Regions
Regions correspond to landmasses isolated millions of years ago by continental drift
Over the course of isolation, animals and plants of different regions evolved independently and developed distinctive characteristics
Australian - Australia and SP Islands
Longest history of isolation from the rest of the world; few exchanges with Oriental
Oriental - Most of SE Asia
Somewhat isolated from the rest of the tropical world, but had exchanges with Palearctic, Ethiopian, and Australian
Neotropical - South/Central America
Isolated from Nearctic until =3 MYA (Formation of Isthmus of Panama); had many exchanges with Nearctic and few with Ethiopian
Nearctic - North America
Maintained connections to Palearctic since =140 MY until Beringia flooded =11kya; still had many exchanges with Palearctic and Neotropical
Palearctic - Eurasia and North Africa
"Close" to many other regions; had many exchanges with Nearctic, Oriental, and Ethiopian
Ethiopian - Most of Africa
Central location, but somewhat isolated; still had many exchanges with many other regions
Cosmopolitanism and Endemism
Two terms that essentially mean the opposite…
Cosmopolitan Species
Species with very wide distributions (natural or artificial) that encompass a very broad geographic area or many different geographic areas and ecosystems
Distributions are often large and can be disjunct
Usually, generalists who can adapt to a wide range of ecological conditions
Endemic Species
Species whose distributions are restricted/isolated to a specific geographic area and ecosystem
Distributions are often small and generally contiguous (i.e., not disjunct, unless a species is limited to a single archipelago)
However, term can be used at different scales (e.g., Puerto Rican endemic, Caribbean Endemic, Neotropical Endemic, etc.)
Usually, specialists who generally cannot adapt to a wide range of ecological conditions
Endemics are often found (or have been found) on single Islands.
Example: Dodo, Mauritius Island
Endemics Often Need Protection!
Rapoport's Rule
Example is for birds, but trend also exists for other taxa
Regions of High Endemicity = High Biodiversity
Near Equator Highest Endemism & Diversity
Towards Poles Lowest Endemism & Diversity
Tropical Rain Forests
7% Earth's Surface
50% Earth's Species
Tundra and Deserts
Fewest Species
Determinants of Biodiversity
Why do different places vary in Biodiversity?
Ease vs Difficulty of Survival
Hospitable vs Harsh Habitats
Stable vs Unstable Habitats
High vs Low Diversity
High diversity may indicate more food sources and microhabitats; low diversity usually less…
Within temperate zones, bird species richness slightly increases with increasing productivity
However, the principal determinant of bird diversity seems to be structural diversity of vegetation
In areas of 5-20 ha:
6 species in grasslands
14 species in shrublands
17-24 species in forests
Why are some locations more/less diverse than others?
High vs Low Latitudes
For most organisms, tropical conditions appeared on earth much earlier than colder conditions.
Tropical and subtropical zones cover more area than temperate and polar regions
Latitudes towards the poles experienced drastic fluctuations in climate during the Ice Age of the past 2 million years
Tropical climates/ecosystems are generally more stable on a yearly basis than other climates/ecosystems
Landmass Sizes and Distances (e.g., Islands)
Equilibrium Theory of Island Biogeography…
Largest, closest islands should have most species
Smallest, most isolated islands should have fewest species
Convergence Defined
The independent evolutionary development of similar adaptations and/or other derived characters that occurs after two or more species lineages have diverged
Due to geographically separated species being exposed to similar selection pressures (i.e., similar climates, food sources, environmental conditions, niches, etc.), not shared ancestry
Through this process, divergent lineages come to resemble one another more than their ancestors did
Full Convergence: Similar niches and similar appearances
Niche Convergence: Similar niches but different appearances
Example: Toucans in South America and Hornbills in Africa and SE Asia
Full Convergence
Eagles & Hawks, Falcons, and Owls
New World Vultures Old World Vultures
Full Convergence: Flightlessness in Ratites
Full Convergence
Wing Functional Diversity
Wings used for aerial flight only
Wings used for both submarine and aerial flight
Wings used for submarine flight only
Niche Convergence
Limpkin, Snail Kite, Cattle Egret, Brown-headed Cowbird
Honeyeater, Honeycreeper
Sunbird, Hummingbird - Certainly, on their way to full!
Convergence Across Time
Hesperornithines + (100-65 mya)
Common Loon (extant)
At the time when Synapsids and Sauropsids diverged, amniotes had evolved relatively few derived characters associated with terrestrial life…
Both lineages independently evolved many advanced characters that were advantageous for terrestrial life.
Both Lineages Independently Evolved:
Respiratory and excretory systems that conserve water
Respiratory systems that are compatible with more intense physical activity via high rates of lung ventilation
Fast-moving predators that could pursue fleeing prey, as well as fast-moving prey species that can escape predators
Lineages capable of sustained flight
Lineages that became endothermic
Lineages with four-chambered hearts
Extensive parental care and complex social behavior
Fins and fusiform body plans in sharks, dolphins, ichthyosaurs, and penguins