Resource Acquisition & Allocation Ecological events and their outcomes, such as growth,...

Resource Acquisition & Allocation

• Ecological events and their outcomes, such as growth, reproduction, primary production and population size, are often regulated by the availability of one or a few factors or requisites in short supply, whereas other resources and raw materials present in excess may go partially unused


• This has become known as the ‘law of the minimum’

• E.g. in arid environments, water is general limiting…other systems?


• At the population level, we frequently see food, predator or climate, limiting them

• However, there may be other factors as well• E.g. increasing nestboxes doubled the blue tit

population in Britain

http://www.pbase.com/tirc/image/54151593


• However, more often than not a single factor is not limiting but contributing and acting synergetically with other factors to limit distribution and/or abundance


• A similar concept is known as the ‘law of tolerance’ in which too much or too little of anything can be detrimental to an organism

• Think of how that may apply to a lizard?


• Consider the relationship between jumping distance and temperature in a frog


• Organisms can be viewed as a simple input-output systems, with foraging or photosynthesis providing an input of materials and energy that are turned into offspring


• In OFT, the ‘goal’ is usually assumed to be maximized is energy uptake per unit time (LRS vs. fitness, but fitness is typically used)

• For species without parental care, reproductive effort has been estimated by the ratio of calories devoted to eggs or offspring compared to the females caloric intake


• However, most studies do not do a great job of correlating ‘input’ with ‘output’

• Similarly, few population biologists have paid any attention to the ‘input’ side of the equation

http://www.ajkids.com/


• Any organism has a limited amount of resources available to devote to foraging, growth, maintenance, and reproduction

• The way in which it makes those decisions is of fundamental interest to evolutionary ecologists as they represent a gradient of life-history strategies


• Being stressed on any one environmental variable are consequently less able to tolerate conditions along other variable gradients

• Various tolerance and performance curves (Fig. 5.2) are presumably subject to certain constraints

• For example, the breadth of a tolerance curve cannot be increased without a subsequent reduction in height (hence, trade-offs)


• For example, consider a predators mouth

• There is an optimal prey size• In a super-productive

environment, a utilization curve might be a single spike with little or no variance…why?

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• Optimal foraging for a wagtail may not be what you think


• It is certainly true that a generalist predator is not as efficient as a specialist

• So which is better?

• More later…


• Time, matter, and energy budgets vary widely among organisms

• E.g. iteroparous vs. semelparous


• Even within a species, it varies seasonally as well as annually

• Male songbirds and territory defense varies widely throughout the year

• Parental-offspring conflict• E.g. red squirrels


• Parental-offspring conflict• E.g. red squirrels, lactating females spend 323

kc/day vs. 117 kc/day for males


• In plants we see some species ‘go to seed’ while still small in bad years (others may skip it entirely) compared to rapid growth in others


• Time and energy budgets can provide a useful transition between foraging influences and reproduction

• Some trade-offs are obvious: as long as foraging is profitable, it provides additional energy for everything else, but it does come at the expense of time


• Thus profits of time spent foraging are measure in matter and energy while costs take on units of time lost

• Conversely, increased time spent on nonforaging activities confers profits in time while costs take the form of decreased energy availability


• Thus, it may be that the optimal allocation of time and energy ultimately depends on how costs in each currency vary with profits in the opposite (however, they need to be converted into a common currency to better understand trade-offs)

• Costs and profits in the time might be measured empirically in energetic units by estimate the net gain in energy per unity of foraging time


• E.g. if all potential foraging time is equivalent, profits would vary linearly with costs; the loss associated with nonforaging activities would be directly proportional to the amount of time devoted to such activity


• It is also important to remember certain time periods favorable to foraging return greater gains in energy gathered per unit time than other periods (consider the risk of a predator)

• Ideally, we would like to measure an animal’s foraging efficiency and its success at budgeting time and energy into LRS


• Foraging and reproductive activities interact in another important way

• During periods of plenty or when reproduction in unlikely or unfavorable, they gather and store materials and energy (which can they be utilized for other activities)


• Prey density can strongly affect an animal’s time and energy budget

• Rock Pipit: a mild winter spent 6.5 hrs feeding, 1.75 hr resting, 0.75 defending

• Harsh winter spent 8.25 foraging, 0.65 hr resting, 0.1 hr in defense


• Harsh winters demand more food • Also, low density food is not worth defending!


• Time and energy budgets are influenced by a multitude of other ecological factors including body size, mode of foraging, mode of locomotion, vagility, trophic level, prey size, resource density, environmental heterogeneity, rarefaction, competition, risk of predation and reproductive tactics


• Leaf tactics: a wide array of sizes and shapes, simple and compound, deciduous or coniferous, and more


• However, some leaves are much more costly to produce than others

• What influences the type of leaf an organism should produce?

• Influence of location? (ht., light, water, temperature)

• Tropical leaves lacking lobes?• The repeating nature of leaves throughout the

world suggests what?


• The end…

Resource Acquisition & Allocation Ecological events and their outcomes, such as growth,...

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