Energy flow Flashcards
Two approaches to energy flow
Hierarchical
Primary producers/autotrophs, “green plants” -> Herbivores -> 1st carnivores -> 2nd carnivores -> top carnivores
all lead to decomposer
Network
Not linear relationship but somewhat hierarchical
In both models, energy is captured by photosynthesis and flows through the ecosystem in the form of carbon-carbon bonds until ultimately released as heat
How is carbon a ecological “currency”
Ecological costs (growth, reproduction, defense)
Energy is a limiting factor: light (trees / forests), food
Energy is used only once and not received
Gross Primary Production (GPP)
GPP = rate of fixation of C or energy by photosynthesis
Units = g C /m2 / month (year)
in the lowland tropics, monthly GPP corresponds water availability
Lowere dry-season GPP is balanced by higher wet-season GPP, so the annual total is similar for deciduous and evergreen forest in the tropics
Net ecosystem productivity (NEP)
GPP - Total ecosystem respiration = NEP
Total ecosystem respiration includes not only what is respired by plants but also what is respired by soil organisms
NEP estimates vary widely based on the analytical methods used. But consistently, evergreen broadleaf forests are expected to have the highest NEP values, followed by savannah
NEP is highest but also most variable in the tropics, meaning current NEP estimates are reather unreliable
What is the result of NEP in forests?
Stored in Biomass
Lowland dipterocarp forests have abouve ground biomass > 400 Mg / ha
90% of biomass is contained in large trees, which can be remnoved by logging
Post-logging recovery of carbon stocks is slow
Similar to NEP, biomass is also highly variable across tropical ecosystems
Reasons for carbon accumulation (sink)
CO2 fertilization
Growing season extension
Sisturbance recovery
Reforestation
Nitrogen deposition
Soil organic matter accumulation
Mineral bonding
from strong to weak from short to long duration
Reasons for carbon emissions (source)
Fire
Heatwaves
Windthrow
Drought
Warming-induced respiration
Pest infestation
Permafrost thaw
Slide ??? violest with circles
carbon flows
Carbon sequestration by global foerst and coastal systems
Tropical forests
Boreal forests
temperate forests
-> all below 10 g C / m2 / yr
Salt marshes
Mangroves
Mangroves
-> over 100
Herbivory: taking advantage of the most available resource
Leaves are vulnerable because:
they must be thin
they mus be high protein for the photosynthetic machinery
they must be exposed
they must be replaced at intervals, which requires going through a softer, more nutritious, young-leaf stage
Thus, leaf herbivory is widespread and dynamic; the plant-herbivore interface is widely studied by ecologists
Most herbivory is by insects
But some mammals specialize on foliage (leaf monkeys, elephants)
Carnivores (vertebrate carnivores) - Invertebrate-specialist carnivores:
all < 15 kg body wight and mostly < 5kg
This is because maximum rate for harvesting small items of food does not increase as the animal gets bigger, so a tiger cannot specialize on insects
Examples in SE Asia: tarsiers, pangolins, shrews
Aerial insectivores
Bats dominate at night, birds during the day. bats also take some insects from leaf surfaces, while different bird species have specialized on different surface types
Vertebrate-feeding carnivores
Killing adult vertebrates is a difficult task, particularly if the prey is a similar size to the predator
In Asia this niche is dominated by:
members of the mammalian order Carnivora
snakes
Diurnal and nocturnal birds of prey
Minor groups include crocodiles (near water) and large monitor lizards, plus non-Carnivora mammals and other bird groups, such as hornbills
Limits to carnivores
Carnivore density is controlled largely by prey availability
Endotherms (mammals, birds) need c. 10’000 kg of prey to support c. 100 kg of a carnivore species
Ectotherms (snakes etc) need far less, as they do not use food to maintain body temperature
Ectothermy allows more flexible body form, while year-round warmth in the tropics reduces the advantages of endothermy
scavenger
eat prey that are already dead
Benefit: prey already dead, no size constraint on prey, so theoretically widely available food
risk: competition with microbes and other scavengers
Vultures
obligate vertebrate scavengers
Neotropics: vultures acavenge on dead vertebrates in forest, which they detect by smnell
Old world vultures: find prey visually
flight: soaring is the only sufficient way to cover enough ground to find carrion
Coprophages
Consumers of vertebrate feces
Herbivore feces are chemically similar to detritus but physically very different. They are dominate by specialized “dung beetles” which rear their young in it
“Rollers” roll a ball of dung away from the dung pile before burying it
Detritivores
Detritus is cycled through detritivores multiple times, losing any recognizable plant structure and eventually ending up as decay- and digestion-resistant humic compounds
Detritivores specialize along this “humification gradient” from fresh litter or wood to humic compounds dispersed in the soil
Note: many invertebrates in the litter layer are not detritivores, but feed either on microorganisms or on the detritivores
Most dominant detritivore
Termites
Appear to be the most improtant detritivores in lowland tropical forests, in part because they are very diverse
Different species specialize on different parts of the gradient
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How are relationships described and quantified in food-web?
Observational
Direct measurements (experimental)
Indirect evidence
Indirect evidence
Given two isotopes of Carbon (13C and 12C) plants will fix 12C more than 13C, therby fractionating it in the plant cells. THis is a
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Are food webs and ecosystems controlled by top-down or bottom-up processes?
Much of the early ecological literature emphasized bottom up (productivity) controls on ecosystem stability (perhaps because energy flows up the chain?)
Recent literature emphasize the importance of top-down (predation) controls the ecosystem stability
