interactions between organisms in tropical rainforests (lecture 5) Flashcards
How did herbivores differentially affect growth and survival of three dominant species in African tropical rainforests in gaps and understorey?
- Norghauer & Newberry, 2013
- What were the aims of the study?
- set out to examine 3 hypotheses:
- most light demanding species, Microberlinia bisulcata is eaten and has its growth in gaps impacted to a greater extent than either Tetraberliner species (T. bifoliolata; T. korupensis)
- leaves of all three species damaged to a greater extent in gaps than understorey
- protection from insect herbivores enhances seedling survival of all three species more in understorey than gaps
- implications for competitive ability of 3 species and their survival when gaps open
How did herbivores differentially affect growth and survival of three dominant species in African tropical rainforests in gaps and understorey?
- Norghauer & Newberry, 2013
- What was the experimental design?
- three closely related canopy tree species (T. bifoliolata, T. korupensis & M. bisulcata
- M. bisulcata is the least shade tolerant (most light demanding)
- 320 gaps & paired understorey sites containing seedlings of the three species
- species with less than 5% herbivory marked
- closed mesh cage to exclude herbivores placed over half of seedlings
- open mesh cage over remainder (control)
- height, leaf number, herbivore damage assessed
How did herbivores differentially affect growth and survival of three dominant species in African tropical rainforests in gaps and understorey?
- Norghauer & Newberry, 2013
- What were the results of the study?
- height growth rate greater for all species in gaps than shade with or without herbivory
- relative growth rate low in the understorey
- seedlings persisted in shade
- M. bisulcata had a higher RGR height than other two species in gaps in absence of herbivores
- no difference between species when herbivores present
- herbivores reduced number of leaves of M. in gap but neither T. species
- in understorey herbivores reduced leaves of M. & T. bifoliolata but not T. korupensis
How did herbivores differentially affect growth and survival of three dominant species in African tropical rainforests in gaps and understorey?
- Norghauer & Newberry, 2013
- What were the conclusions of the study?
- in understorey light in limited supply compared to gaps
- exposure to herbivory which reduces leaf area for light capture
- more detrimental under low than high light conditions for M. bisulcata/T. korupensis
- T. bifoliolata survived equally well in both treatments in both light environments
- suggests resistance to being eaten
- suggests seedling leaf physiology of its seedlings confers strong ability to persist under low light conditions
Why have plants evolved defences against herbivory?
- plants evolved array of biotic, chemical, mechanical & phenological ways to attack/poison/starve or avoid herbivores
- interaction of herbivores & young leaves of seedlings important in regulating trophic dynamics
- determines herbivore population sizes/seedling persistence
- insects most important leaf material consumers in tropical forests
- vertebrates, fungi, pathogens have effect also
tropical gap specialists - insect herbivores v diverse
- impacts on plants obvious or hidden
How do plants defend themselves?
physical defence:
- e.g. spines on stems of rattans/bamboos/acacias
- e.g. stinging plants like seed pods of Mucuna climbers
- both deter vertebrate herbivores
chemical defence:
- e.g. trees w toxic bark to deter elephants in Ugandan forests (like Antiaris toxicaria)
How much damage is inflicted by herbivores in tropical forests?
- average annual - herbivory in temperate forests 7%
- 11% in tropical shade plants, 48% in sun plants
- invertebrates most herbivory
- major damage window when leaves young & expanding
- 75% lifetime damage of long lived sade plants in a few weeks when leaves expanding
- species lose 12-74% of area during lead expansion
Why are different species damaged differently by herbivores?
- plants invest in range of leaf defences
chemical defences:
- alkoloids/tannins/phenols
mature leaves:
- toughness, fibre content, other physical defences
expanding leaves:
- rapid expansion to minimise damage
- synchronous leaf production so herbivores satiated
- delayed greening of young leaves
- extra-floral nectaries, ant defence
Why do young leaves of many tropical species exhibit delayed greening?
- delayed development of chloroplasts
- energy & nitrogen losses reduced
- young expanding leaves look white or varying shades of red/purple (anthocyanins)
- leaves w delayed greening
- less nutritious
- less attractive to herbivores
but
- reduces photosynthesis
- prevalent among understorey plants where photosynthesis is limited by shade anyway
How do ant-plant mutualisms protect leaves?
- plants provide extra floral necctaries, food bodies, nesting sites called domatia
- ants will in return agrressively attack herbivores (invertebrate & vertebrate)
- Crecopia plants
- protected by Azteca in Neotropics
- Macaranga plants
- protected by Crematogaster in Asia
How are Macaranga bancana colonised with Heart Gaster ants?
- obligatory relationship
- usually colonised as saplings
- queen chews through shoot to enter young plant
- seals self inside, lays eggs
- cares for larvae until they become worker ants
- workers look after subsequent batches of eggs
What do Macaranga bancana plants provide to Heart Gaster ants?
- stipules
- brownish red structures along stem
- white starchy bodies on underside of stipules
- food for ants
- ants farm insects of Coccus genus in stem hollows
- feed on honeydew that sapsuckers secrete
What do Heart Gaster ants provide to Macaranga bancana plants?
- ants protect plant against herbivores, insects, pathogenic fungi
- vibrations when insects/other large organism lands
- alerts ants
- swarm out of tiny holes on stem surface
- raise gaster (rear portion) attack intruders with formic acid
What did Kursar and Coley (2003) study?
- survey of defensive traits of young leaves
- over 200 related species Africa, S.E. Asia, Neotropics
- traits classified into 2 syndromes
- defense syndrome: well-defended young leaves
- escape syndrome: rely on rapid expansion to minimise young vulnerable leaf stage
- not always discrete classes
- continuum
- defenses organised in suites of traits
- suggestive of convergent evolution
How did Coley et al., (2005) study defence of closely related Inga species?
- Inga goldmanii
- Inga umbellifera
- Barro Colorado Island, Panama
- 1-3m tall saplings
measured:
- ant visitation to extra floral nectaries
- change in leaf size
- rate of growth
- concentration/bioassays of leaf secondary metabolism (measure of potential defence compounds)
- herbivore communities feeding on each species
