ESS W1 L2 - biogeography and biomes

biogeography and biomes

Biogeography definition 1:

•   ‘the science that attempts to document and understand spatial patterns of biodiversity’

  • Brown and lomolino, 1998

Biogeography definition 1:

•   the study of the distribution of organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living things’

  •   Ibid

Biogeography: what explains the uneven distribution of species across the planet:

More biodiversity in the tropics (red etc. colours)

Biogeography: what explains the uneven distribution of species across the planet: example

Mediterranean type ecosystems

Mediterranean type ecosystems

• Common traits:

  • Seasonal climate – wet winter, dry summer

  • Influence of fire (wildfires)

  • Similar vegetation

  •   Species rich

• these common ecological factors lead to dominance by evergreen shrubs and thick leaved (sclerophyll) trees – adapted to fire and retain water

• We need to understand ecology to do biogeography

   Mediterranean type ecosystems (5)

• chaparral - california

• fynbos - cape

• maquis - med basin

• matorral - central chile

• kwongan - australia

role of history in med ecosystems

•   do mediterranean type ecosystems share a common origin and evolutionary history?

• Seems unlikely as their floras are comprised of different genera and species

• But there are a few plant families (e.g. Rhamnaceae (buckthorns), and Proteaceae (proteas) ) that are common to more than one MTE

• How did they get there – tectonics or dispersal

 

Plate tectonics: vicariance:

• Vicariance refers to some kind of event (continents breaking apart, mountain ranges uplifting) physically separating population

• Ancestral population - geographic isolation -speciation

• Leads to genetic divergence – become different species and wouldn’t be able to reproduce

Dispersal:

• Refers to the movement of animals and plants moving across land or water to reach new areas

• Ancestral population - geographic isolation - speciation

• Leads to genetic divergence – become different species and wouldn’t be able to reproduce

Zoogeographic maps:

•   1876 – Wallace created a map of the difference in animal species throughout the globe

• Divided the globe into terrestrial zones with homogenous fauna (animal life)

• Match up with the continental plates

• Not so different to recent maps produced using phylogenetic data (holt et al 2013)

modern maps

• use information from phylogenetic trees

• Phylogenetic trees use molecular (DNA or protein sequences) techniques to understand evolutionary lineage between species or taxa

•   Biogeographic realms reflect broad distributions of terrestrial species

Map of evolutionary uniqueness:

• How unique species are to a particular place

• Based on data for 21, 037 species of vertebrates

• Regions coloured in dark red are the most evolutionary unique

• Antarctica isn’t included in the analyses

Unique animals of Australia: marsupials

maternal pouch

• koala

• kangaroo

• wallaby

• sugar glider

• tasmanian devil

Unique animals of Australia: monotremes

egg laying animals

• platypus

• echidna

Plate tectonics:

• Supercontinent Pangea- separated over 250 mil years

• Gondwana breaking into smaller continents over 180 mil years

• Australia – approx. 140 mil years ago – one of the first continents to separate from Gondwana

• Life started to evolve when all the continents were connected

• About 60 mil years ago – most continents isolated

Legume family phylogeny:

• Legumes (pea and bean) dominate in tropical forests of South America and Africa

• High diversity: 20,000 species

• Originally thought legumes originated together when Africa and South America were joined as part of the super continent Gondwana.

• Africa separated from S America (when part of Gondwana) 100 - 140 million years ago.

•   This vicariance instigated the diversity in species.

• However, with new molecular techniques we have a greater insight in to the phylogeny (evolutionary relationships) of species in Africa and South America

legumes continued

• Molecular clock technique identifies the timing of evolutionary splits

• Commonality in legume species between Africa and S America occurred until 10 million years ago.

• This is ~90 million years after Gondwana separated.

• Dispersal must have been happening across major oceans

dispersal

• The spread, isolation and disjunction of organisms reflect long-distance dispersal

• Species had reached newly formed volcanic islands never connected to land

•   via ocean currents, winds, or carried by traveling animals, most recently by humans

anthropogenic dispersal:

• The movement of animals, plants, fungi, or microorganisms by humans across biogeographic barriers to an environment where they are not native (transport and trade).

• Factor in global biodiversity loss – as introduce non-native species

  • Homogenization of habitat and species composition

• Anthropogenic dispersal is accelerating

• Linked to international travel and tourism

• E.g. Hawaii – high level of non-native plants

Conservation:

• Biogeography helps to predict how biodiversity will change over time and to develop solutions to help biodiversity respond to future environmental threats

• Helps us understand:

  • Diversity pattern overlaps

  •    Landscape ecology

  • Conservation assessments

  •   Future predictions

  • Extinction risk

Biome definition:

• Continually evolving definition

• ‘biomes are major vegetation formations with distinct physical forms (physiognomies) and ecological processes that can be characterised at a global scale’         

  • Pennigton, lehmann, and Rowland 2018

• Ecological processes – mechanisms that sustain life

  • Energy flow, nutrient cycling (biogeochemical cycles), primary production (photosynthesis), decomposition (soils), water cycle, population dynamics (competition, dispersal ecological succession)

Terrestrial biomes – oversimplified:

Controls on biomes distribution:

• Is it all climate?

• Since 1830s, the major driver of vegetation patterns/ zones has been understood to be climate

• diagram = whittakers biome scheme

Species inventory from tropical lowlands:

• Biomes aren’t just climate controlled

• Different species in savannas on different continents – S, America and Africa, and in different moist forest – Africa and Asia

What are biomes:

• Dexter, pennington et al 2015

• The same biogeographic realm/ region can contain different biomes

• This suggests a key role for independent evolution of adaptations required in different ecological settings in different places

• SDTF = seasonally dry topical forest

How to define a biome:

• Alexander von Humboldt (18^th-19^th C)

• Recognised that vegetations in different locations may look similar but are taxonomically different

• Environmentally similar but isolated regions have distinct biotas. So cannot use taxonomic composition to define biomes at global scale

• Need to think about ecological processes

 

Climatic variables are an important control of biome distribution:

• Air temperature

•   Precipitation

• Net radiation

Bioclimatic variables are important controls in biome distribution:

•   More than climate

• Precipitation – evaporation

• Run off/ water surplus

• Soil moisture

• Other key variable often neglected:

  • Soil fertility/ pH factors (edaphic factors)

  •    Presence of regular, natural fire

Focus on south America:

• Tropical Rain forest, seasonally dry tropical forest and tropical savanna

• Neotropical realm - diagram

Biome 1: tropical rain forest:

• Characterised by:

  •   High (>25m), closed (continuous) evergreen canopies – dense forests

  • Annual precipitation >2000mm approx.

  •   Little to no dry season

Biome 2: tropical savanna:

• Grassy woodlands:    

  • Open canopies, tree cover from 0-80%

  •    Continuous ground layer of grasses (>50%)

  •   Dry seasons (3-6 months)

  • Rainfall:

    • 800-2500mm south America

    • 300-1500 mm Africa

    • 350- 2000mm Australia

  • Nutrient poor, acid soils in neotropics

  • Evergreen tress

  • Natural fire prevents forest – fire adaptations

 

Biome 3: seasonally dry tropical forest:

• Often closed canopy

• Deciduous trees

• Few grasses

• Seasonally dry (same climate as savannas)

• But richer soils

• No fire

• Dominance of succulent plants (cacti in neotropics) not adapted to fire

 

Lowland tropical biomes in Latin America:

• Fire and soil are key controls in the distribution of dry biomes in latin America

• It’s not all about the climate

• As savanna and dry forests grow in the same place

Biomes and bacteria:

• Different global biomes (different vegetation and climate) have different bacterial diversity and biomass

• Bacteria are important for ecosystem functions:

  • Nutrient recycling (carbon, nitrogen and phosphorous)

  •    Decomposing dead material

  •   Plant growth

  • Water recycling

Anthromes:

• Human biomes or anthrome

• Global ecological patterns shaped by human interactions with ecosystems

• Mosaic of different land uses and covers

• Terrestrial: managed forests, pasters, crops, plantations, villages, dense urban settlements

Anthropogenic biome transformation

Human impact on biomes:

•   Human impact via:

  • habitat loss

  • Deforestation

  • Pollution

  •   Climate change

  • Invasive species

  • Hunting

  • Farming/ crops

  • Controlled burning

• Human induced climate change set to impact biomes further

 

Summary:

• Biogeography – understanding the spatial patterns of biodiversity across the planet

• Biogeographic regions = diversity in relation to evolutionary lineages – dispersal and vicariance

• Biomes – how to define them

• Biome = species diversity in relation to ecological (not just climate) processes

• Factors like soil condition and fore occurrence are important and will be examined more