herbivore (terrestrial lecture 12) Flashcards
Why is the world green?
- green world implies plant populations limited by resource availability, not herbivory, disturbance
Effect of herbivores in Savannahs
- what is greater than in other ecosystems?
- what do large animals reduce, how, how much? Mahli et al 2016
what do large bodied grazers do?
Savannah
- consumption in herbivores is greater in savannahs than other ecosystems
- large animals reduce woody plant cover 15-95% through herbivory, trampling and plant breakage (Malhi et al., 2016)
- large bodied grazers can open up poor quality tall grasslands to short grass lawns
Plant functional traits and community characteristics of grazing lawns?
Plant functional traits:
- nutrient rich & palatable
- grow fast in wet season
- leaves rather than stems
- tolerate grazing
Community characteristics:
- highly productive
- some evidence of enhanced nutrient cycling
What are herbivore functional traits? What do they feed on? What do their mouths look like? Teeth? Salivary glands? Examples?
- grazers
- browsers
- many bovids/elephants are what
- grazers = grass feeders
- “lawn mowers” = wide muzzle, small mouth openings, stiff lips
- high crowned teeth, abrasive wear from ingesting grit
- small salivary glands and liver, grasses aren’t chemically defended
(e. g. bison, white rhino)
Browsers = feed on woody plant foliage
- narrow muzzle, largemouth opening, long tongue and prehensile lips
- avoid structural defences and select leaves
- low crowned teeth bc woody plat foliage non abrasive
- large salivary glands and liver bc woody plants are chemically defended
(e. g. giraffe, black rhino)
many bovids (e.g. antelopes) and elephants are mixed feeders
What are spiny woody savannah plants associated with?
- medium-sized mixed feeders (e.g. bovids)
- large-bodied browsers (e.g. giraffes)
- open vegetation
- dry fertile environments
- low fire frequency
Did herbivores and resistance co-evolve?
Spiny plant diversification corresponds to colonisation of Africa and diversification by bovids (Charles-Dominique, 2016)
What is the trade-off between fire and herbivory?
Pole vs cage architecture
Pole architecture:
- fire adapted
- unbranched
- frequent fires
- topkill trees
- thin bark
- starch storage
- rapid sprouting
Cage architecture:
- herbivore resistant
- highly branched
- deters browsers
- infrequent fires
- thick bark
- non-flammable
Why are large herbivores less selective feeders?
- can obtain larger proportion of their energy requirements from abundant low quality plants than small bodied (e.g. elephants vs mice)
large animals
- ingest more food relative to gut length
- have longer guts and food retention = greater digestive efficiency
- have a lower metabolic rate
SO
- large animals have greater energy intake relative to requirements but need large quantities & therefore productive ecosystems
Plant quality-quantity relationships
- large herbivores can consume poor quality but need high quantity
- small herbivores need higher quality but smallers quantities
- quality decreases w higher rainfall but biomass higher w higher rainfall
- greatest herbivore diversity at intermediate rainfall
What structures herbivore communities at large scales?
plant-herbivore interactions
Functional traits:
- plant and animal functional traits interact to structure communities
Body size:
- functional interactions modified by animal body size
Climate and soil:
- environmental gradients of rainfall, soil fertility interact with plant quality and quantity to set large-scale distributions of herbivores.
Herbivore response to predator presence
Estes et al., 2011:
- Venezuelan mainland vs Lago Guri island
- Yellowstone national park
(Estes et al., 2011)
- Venezuelan mainland forests - remain green, herbivores controlled
- Lago Guri island forests, no predators, herbivore populations erupted, foliage reduced
- Yellowstone national park
- before wolves reintroduced, elk heavily browsed willow
- after, elk avoided open habitats, fear of predation
Disease impacts (parasites) on herbivore populations and fire
Estes et al., 2011:
(Estes et al., 2011)
- East Africa
- rinderpest reduced wildebeest populations
- woody plants invaded, increasing fire intensity/frequency
Predator impacts on soil nutrients
Estes et al., 2011:
(Estes et al. 2011)
- Aleutian Islands without Arctic Foxes have richer greenery
- foxes prey on seabirds which export nutrients especially phosphorous from sea to land
How do predators and parasites structure herbivore communities at large scales? (top down control)
Trophic cascades
Indirect effects
Trophic cascades:
- predators and parasites (e.g. diseases) limit herbivore populations with cascading effects to plant populations
Indirect effects:
- predators and parasites can have unexpected indirect effects on ecosystem function (e.g. fires and soil nutrients)
