interactions between organisms in tropical rainforests (lecture 5) Flashcards
(18 cards)
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
What differences did Coley et al., (2005) find between the defence strategies of closely related Inga species?
- suffered similar levels of herbivore damage
- but done by different herbivore communities
- 3 herbivore species restricted to I. goldmanii, 6 to I. umbellifera
- Homoptera, Orthoptera & leaf cutting ants found on I. umbellifera but not I. goldmanii
- differences in classes of secondary defence compounds (non protein amino acids, flavanoids) in leaves of two species
- I. goldmanii flavanoids more bioactive against herbivores
I. goldmanii
- higher levels of biotic defences
- more extra floral nectaries per leaflet
- attracting more ants than I. umbellifera
I. umbellifera
- fewer but more synchronous flushed
- expanded faster
- delayed greening/low chlorophyll in young leaves
What did Coley et al., (2005) conclude were the defence strategy differences in closely related inga plants?
I. umbellifera: escape strategy
- leaves produced in fewer but more synchronous flushes
- more rapid expansion of young leaves
- delayed greening
- fewer chemical defences
- no ant defences
I. goldmanii: defence strategy
- little synchronous leaf production
- slow leaf expansion
- normal chloroplast development
- more bioactive chemical defences
- plant protected by ants
What did Coley et al., (2005) summarise about defence strategy differences in closely related inga plants?
- closely related but diverged in terms of defence adaptations
- evolutionary trade off
- energy devoted either to defence or growth for rapid escape
- each defence strategy gives similar result
- why neither strategy competitively excluded
- allows these two closely related species to co exist in same habitat
- two other closely related Inga species in Amazon (Coley & Kursar, 2014)
