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Leaf Tactics. Light Water availability Prevailing winds Herbivores Costs and Profits of Leaf Size, Shape, and Placement. Leaf Tactics. Similar types of leaves have evolved independently in different plant lineages subjected to comparable climatic conditions
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Leaf Tactics • Light • Water availability • Prevailing winds • Herbivores • Costs and Profits of Leaf Size, Shape, and Placement
Leaf Tactics Similar types of leaves have evolved independently in different plant lineages subjected to comparable climatic conditions Compound leaves conserve woody tissue Small leaflets in hot dry regions, but larger under warm moist conditions Shade tolerant understory species usually have larger and less lobed leaves than canopy species Lobed leaves do not cast as dense and solid a shadow as do leaves with continuous margins
In lowland wet tropical rainforest,trees tend to have large evergreen leaves In chaparral, plants tend to have small sclerophyllous evergreen leaves Arid regions tend to support leafless stem succulents such as cacti or plants with entire leaf margins Cold wet climates tend to support plants with notched or lobed leaf margins
Plant Life FormsEvergreen vs. DeciduousMonolayered vs Multilayered plantsShade ToleranceXerophytic vs. Mesophytic leavesAlso Hydrophytes (water lilies)
Foraging Tactics and Feeding EfficiencyCosts and Profits of ForagingAn optimal foraging tactic maximizes the difference betweenforaging profits and their costsFood = matter and energy for maintenance and reproductionHazards: exposure to predators, loss of time for other activitiesSit-and-Wait ambush predators (e.g. spiders at webs)Widely foraging active hunters (go out and find prey)Search Time (per item eaten) versus Pursuit Time (per item eaten)Search for all possible prey items, but pursue them one at a time Prey items can be ranked from most preferred to least desirable
“Economics of Consumer Choice” Assumptions:a) Environmental structure is repeatable, with statistical expectation of finding a given resource (habitat, microhabitat, or prey item)b) Food items can be arranged along a continuous spectrum, such as by size or energy rewardc) Similar phenotypes are closely equivalent in harvesting abilitiesd) Principle of Allocation applies: no one phenotype can be maximally efficient on all prey typese) An individual’s economic “goal” is to maximize its total intake of food resources Robert MacArthur
“Economics of Consumer Choice”Four Phases of Foraging: 1) deciding where to search 2) searching for palatable food items 3) upon locating a potential food item, deciding whether or not to pursue it 4) pursuit itself, with possible capture and eatingSearch and pursuit efficiencies for each food type in each habitat are entirely determined by preceding assumptions about morphology and environmental repeatability. These efficiencies dictate probabilities associated with search and pursuit (phases 2 and 4) . Thus, need to consider only the two decisions: where to forage and which prey items to pursue (phases 1 and 3 above) Robert MacArthur
“Economics of Consumer Choice” (R. H. MacArthur)Clearly, an optimal consumer should forage where its expectationof yield is greatest — an easy decision to make, given knowledge of efficiency probabilities and the structure of the environment (of course, in reality, animals are not omniscient and must make decisions based on incomplete information).The decision as to which prey items to pursue is also simple. Upon finding a potential prey item, a consumer has just two options: either pursue it or go on searching for a better item and pursue that one instead. Both decisions end in the forager beginning a new search, so the best choice is clearly the one that returns the greatest yield per unit time.An optimal consumer should opt to pursue an item only when it cannot expect to locate, catch and eat a better item during the time required to capture and ingest the first prey item.
Physiological EcologyHomeostasis: maintenance of a relatively stable internal state under a much wider range of external environmental conditionsTemperature regulation (thermoregulation)Physiological Optima and Tolerance CurvesAcclimation
Energetics of Metabolism and Movement Ingestion = Assimilation + Egestion Assimilation = Productivity + Respiration Productivity = Growth + Reproduction Ingestion = Egestion + {Respiration + Growth + Reproduction} {Assimilation}------------------------------------------------Homeotherm versus Poikilotherm Ectotherm versus Endotherm
