Biogeography Flashcards
Where do forests not grow?
Everywhere except:
- when it’s too dry
- when it’s too cold
- when it was destroyed by humans
Boreal forest or northern coniferous forest
Long, cold winter and short grwoing seaason (90 - 120 days)
Dominated by evergreen, needle-leaved trees
Temperate deciduous forest
Southern Finland, Sweden, Norway
Europe, parts of USA, Asia
Broad leaved trees, lose leaves in winter
not only in temperate zone also in tropical zone
Longer grwoing season makes it possible to grow cheap new leaves every spring and discard them every autumn / fall
Types of forests in the tropics
Tropical rainforest
Tropical moist forest
Tropical dry forest
Tropical rainforest - definition
Also known as:
- Tropical broad-leaved evergreen rainforest
- Tropical moist forest
Strictest definition is
- minimum precipitation of ca. 2000 mm per year, AND
- No months with precipitation < 100 mm
Year-round growth, so trees are evergreen
What are characteristics of Tropical forests?
highest structural complexity of all forest types
contain most of earth’s biodiversity - they are truly remarkable ecosystems that warrant appreciation, study and conservation
Origins of tropical rainforests
Most modern tropical rainforests are on fragments of the Mesozoic southern supercontinent of Gondwana. Angiosperms arose some time during the Mesozoic (as early as 180 Ma).
Most modern groups of rainforest organisms evolved after Gondwana had broken up and the fragments were widely separated.
Age of Mammals - 65 Ma
The basic argument is that most plants and animals that now inhabit the tropical rainforests did not arise until after the breakup of Gondwana. Therefore, both vicariance and dispersal have played essential roles in shaping the distribution of tropical plants and animals.
Page 15
Phylogenetic patterns reflect earth’s tectonic history
p. 15
Exception Mangrove
globally distributed forest type with species that are very closely related, which contrasts with terrestrial patterns
a unique terrestrially-derived forest type that inhabits tropical low wave energy intertidal zones
Mangroves have evolved water-dispersed propagules - can disperse much further
Global mangrove diversity
Approximately 80 species in 21 plant families
Mangrove forests are defined by trees, dominated globally by the three terrestrial families Rhizophoraceae, Acanthaceae and Lythraceae
Two broad biogeographic regions:
Eastern mangroves - indo west pacific
Indonesia and Australasia
Western mangroves - Atlantic east pacific
Middle and south america
What controls distribution of vegetation?
Temperature and precipitation two major factors affecting distribution
See also page 24
Climate diagrams
Show seasonality of rainfall and temperature in a standard format for ease of comparison between sites.
The rainfall and temperature scales are chosen so that when the rainfall curve is above the temperature curve the climate is wet and when it is below the climate is dry.
See page 25 - 29
Equatorial-type climate
hot and wet all year - no dry or cold season
natural vegetation is tropical rainforest - dominated by evergreen, broad-leaved trees
diagrams: rainfall lines do not cross temperature lines (no dry season)
Tropical wet-and-dry climate = tropical monsoon climate
alternating wet season and 2-6 month dry season
natural vegetation is semi-evergreen or dry-season deciduous forest
Length of dry season is the key environmental variable associated with level of deciduousness in the foerst
diagram: dry season of few month, line is below temperature, temperature line is rather constant
Subtropical climate
Both rainfall and temperature seasonal
natural vegetation is subtropical broad-leaved evergreen forest, as cool dry-season reduces water stress
diagram: Temperature cahnges over season, rainfall not under temperature
Vertical, altitudinal gradient in forest types
Temperatures decline consistently with altitude above sea-level, c. 0.6°C per 100 m
Rainfall varies less consistently, bit usually increases to a maximum and then decreases
All other environmental factors also change with altitude, e.g.
- soil organic carbon content increases
- proportion of UV-B in sunlight increases
-etc.
Forest changes with increasing altitude
Forest becomes shorter and the tree heights are more even
Tree crowns and leaves become smaller
Cold-sensitive tropical plants drop out, while (fewer) cold-tolerant species replace them, leading to an overall drop in plant diversity.
Animal communities also change, e.g. ant number and diversity declines to zero, earthworms replace termites as the dominant soil organisms, bird communities change etc.
Zones along different altitudes
Alpine (above tree-line, > 4000 m)
Subalpine (just below tree-line)
Upper montane
Lower montane
Lowland (up to c.1000 m, from 700 m we start to see change)
-> Changes are often gradual.
What factors affect type of tropical dry forest that will occur?
Soil
fire regime
rainfall
Soil type in lowland forest
sandy, nutrient-poor soils
dominated by small, pole-like trees with small leaves and is known as heath forest or kerangas
Soil type of montane forest
Ultrabasic rock
shorter than forest on other rocks
dominated by one species of gymnosperm
Forest on limestone
tends to be shorter adn have fewer and different species than on other rock types in same area
Peat swamp forests
partly decomposed organic matter has built up above the local water table
peat domes are never flooded so the only nutrient input comes from the rain
see also page 37
Peat is organic matter, so when peat swamp forests are logged and/or drained, they become very susceptible to fire in dry periods, accounting for the regional ‘haze’ episodes and about 3% of total global carbon emissions
5 major rainforest regions today for animal groups
Neotropics - south and central America
Africa - central and west Africa
Asia - SE Asia + NE India, Western Ghats, wet zone fo Sri Lanka
New Guinea + Australia
Madagascar
(plus a sixth region consisting of small areas on many oceanic islands)
Neotropical rainforests
Largest area of rainforest today
Most diverse for plants, birds, butterflies and many other groups
in many ways the most distinctive
From which three main elements was the neotropical rainforest fauna derived?
Groups of possible Gondwanic origin that radiated in S. America during its long period od isolation
Examples:
Groups which arrived (from Africa?) furing the period of isolation (c. 30 m years ago)
Examples: New World primates, Caviomorph rodents
-> probably by “rafting” on massive islands of vegetation washed out to sea during severe storms
Groups which wrrived (from North America) only after the formation of the Panama land bridge, c. 3 million years ago
Examples: Carnivores, Deer, also tapirs, squirrels, mice, shrews among others
Other charasteristic groups (of neotropics) include:
Leaf-cutter ants
Euglossine bees
New World Fruit bats
Hummingbirds
Tanagers
Neotropical rainforests have no
Really large mammals, such as elephants and rhinos
no apes
no honeybees (until recently)
African rainforests
Intermittent connections to Eurasia have reduced their distinctiveness
Drying of the continent has reduced their diversity
Today mostly drier, lower, more open, and less diverse than
other regions (Exceptions: termites, primates very diverse).
Most major rainforest families of animals are shared with Asian rainforests.
Fauna in African Rainforests
most distinctive feature is abundance and diversity of small, medium and very large, ground-living herbivores
(Elephant, Gorilla, Okapi etc.)
Asian Rainforests
Asia and Africa share: bulbuls, pteropodid fruit bats, cercopithecine monkeys, civets, hornbills, apes and elephants
Mammals only in Asia:
Hylobatidae – gibbons
Tarsiidae – tarsiers
Scandentia - treeshrews Dermoptera – colugos (flying lemurs)
Only Asia has forest rhinoceroses
-> only about 65 Javan rhinos and <80 Sumatran rhinos survive
ew Guinean rainforests + Australia
Rainforest covered much of northern Australia in the early to middle Miocene (23-15 million years ago), but has since become restricted to a tiny area in the northeast.
Rainforest in New Guinea is very recent, uplifted above sea-level 10-15 MYA.
By this time, the nearest source of TRF plants and animals was Asia, but only taxa that could cross > 40 km of sea could get there.
As a result:
The lowland rainforest FLORA of New Guinea is largely Asian, although it lacks many typical Asian plant groups.
Fauna of New Guinea
largely non-asian
rats and bats are the only native placental mammals
there are no primates, deer, placental carnivores etc.
marsupials fill the mammalian herbivore, frugivore and small carnivore niches
there are no large mammalian carnivores
bird fauna includes asian groups but also some endeic groups, such as birds of paradise
Madagascan rainforest
Iolated for 90 million years from Africa by a deep ocean barrier
The entire non-flying mammal fauna of 101 species has resulted from only 4 colonization events
The same is true for birds, amphibians and reptiles in Madagascar: few colonization events, adaptive radiation
The tree and shrub flora is about 96% endemic, but most families shared with Africa
Convergent evolution
It is often suggested that convergent evolution of species ensures that niches are filled from whatever lineages are available
-> unrelated species that are similar in different regions and serve same purpose
