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Tropical Biology. The Tropics. “the ‘tropics’ are not a plot of convenient forest in Costa Rica; they are an enormous realm of patchiness, and any theoretical thinking based on presumed general properties is bound to become an in-group exercise in short-lived futility” Paulo Vanzolini.
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The Tropics • “the ‘tropics’ are not a plot of convenient forest in Costa Rica; they are an enormous realm of patchiness, and any theoretical thinking based on presumed general properties is bound to become an in-group exercise in short-lived futility” • Paulo Vanzolini
Paradigm Shift • Temperate View of Tropics – “a place where hummingbirds migrate to escape the harsh winters of the temperate zone” • Tropical View of Temperate Zone – “a place where tropical hummingbirds go to utilize the seasonal abundance of flowers with few competitors”
The Tropicsclimate • Relatively constant temperatures (warm..highs about 31oC and nighttime low of about 22oC) • How much sun does Manus get a yr? How much does NY get? • The tilt and rotation of the earth • The intensity of sunlight
The Tropicsclimate • Relative humidity high (rarely <80%) • Relative constant temperatures (e.g. generally <5oC difference between seasons) • Relatively constant daylength • Can rain almost any day, but seasonality is generally the dominant theme • Annual averages vary dramatically (e.g. Amazon 200cm, western Chile almost 0)
El Niño • There are dramatic events that happen periodically • Originally near Christmas • Unpredictable warming of the eastern Pacific Ocean surface waters near equator • Occurs about every 2-7 years, it destroys the stable weather of westward blowing tradewinds
El Niño • Resulting change in wind can breakdown ocean currents and even reverse flows • Ultimately, not only changes weather patterns in S Am, but all over the globe
Seasonality • Despite the relative ‘constantness’ of so many climatic variables, there is a strong and important seasonality to the tropics
Rainfall Variability Andagoya 709cm 177cm 263cm
Seasonality • Although rain may fall in every month, there is usually a distinct wet/dry season • Sometimes there are additional ‘mini’ wet and dry seasons occurring within each other (e.g. Brazil cerrado-March) • When dry period becomes too pronounced, may shift to a tropical deciduous forest
Seasonality • The seasonality impacts most organisms in the tropics ranging from flowering phenology, seed production, plant germination, timing of breeding, animal migration, fruiting, spawning for riverine species, grazing rates (why and when?), dietary shifts (e.g. ants to termites), behavioral movements
The Importance of Mountains • “a bad earthquake at once destroys out oldest associations: the earth, the very emblem of solidarity, has moved beneath our feet like a thin crust over a fluid; one second of time has created in the mind a strange idea of insecurity, which hours of reflection would not have produced” • Charles Darwin
Mountains • Mountains can impact weather patterns by forming giant walls which act to keep moisture in and prevent it from escaping • For example, up to 75% of precipitation in the central Amazon basin is directly from evapotranspiration from the rainforest itself
Mountains • Rain shadow
Mountains • There can be strong zonation patterns associated with mountains • For example, lowland rainforest transition to deciduous forest, to cloud forest, to an extreme form of elfin forest. After that, it can continue to an alpine shrubland, and an alpine grassland.
Mountain Zones • In general, temperature drops about 1.5oC for every 300m rise in elevation • Tropical forests rarely exceed 1,700m being replaced by subtropical forest (1,700-2,600m) above which only shrubland or grassland habitat persists
Mountain Biology • Mountains also create fantastic opportunities for isolation and localized specialization • Speciation!!
Mountain Biology • Mountains also create fantastic opportunities for isolation and localized specialization • Speciation!! • Consequently, mountain zones have some of the highest biodiversity in the world
Tropical Habitats • Subtropical Arid • Subtropical Moist/Humid • Tropical Arid • Tropical Moist • Savannah • Coastal • What about areas in between? • These are frequently the areas with strong seasonal effects (e.g. tropical deciduous)
Tropical Coastal Ecosystems • Many of the same systems occur in the tropics as temperate (e.g. lakes and rivers), but have very different abiotic influences, which strongly impact the biotic communities inhabiting them • There are also distinctly tropical (or subtropical) systems (e.g. mangrove, coral reef, & seagrasses)
Coastal Ecosystemsmangroves • Forests of mangrove line tropical coasts, lagoons, and offshore islands • Mangrove is not a taxonomic term, but is based upon physical attributes (≈34 sp., 8 sp. in Neotropics) • Tend to exhibit aerial roots, strongly adapted to high salinity, and are taxonomically distinct from terrestrial relatives • Range in size from shrublike to 10-20m tall
Coastal EcosystemsSeagrasses • Closely associated with mangroves, seagrass beds are vast floats that inhabit the clear, shallowsea • True flowering plants, not algae • Spread via rhizomes • System is very productive (higher than most terrestrial or marine systems) • Productivity quickly moves from ‘above water into water’
Coastal EcosystemsSeagrasses • How? Fallen leaves or sticks quickly colonized by bacteria, fungi, and protozoans, concentrating protein • These leaves now ‘grazed’ by shrimp, worms, crabs and various fish (e.g. juvenile snapper and grunts). Process continues again on smaller pieces.
Coastal EcosystemsCoral Reefs • Found in tropical seas surrounding islands and paralleling coastlines • Confined to warm (>20oC, 68oF) waters • Actually an animal (Coelenterata/Cnideria) • Incredibly productive • Lacks large plants, one-celled algaes • Neotropics richness poor (60 vs 700 in Indo-Pacific; 500 Bahamas vs. 1,500 GBR vs. 2000 Philippines) • Alpha diversity vs. beta diversity…similar
Coral Reef vs. Rainforest • High productivity (but low plant diversity) • High S of animals, including predators • Territoriality and sexual selection evident • Extensive examples of co-evolution • E.g. “cleaners” & “false cleaners” • Many cryptic species, warning coloration • Strong importance of periodic disturbance (Connell’s intermediate disturbance hypothesis)
