|Marine organisms face a variety of challenges in their
quest for life and reproduction. They must obtain food for growth and survival,
avoid being food for other organisms, cope with the physical environment,
and have an effective strategy for bringing forth reproducing offspring.
First we will look at Foraging Ecology, the quest for food. Obtaining food is necessary for an organisms survival, growth and offspring reproduction. Without food, almost nothing else about an organisms relation to the world will matter for long.
I. Obtaining food, necessary for: -survival -growth -offspring reproduction
There are many different strategies for obtaining the
necessary food. Organisms generally follow two basic strategies, being
either a generalist or a specialist. A specialist will prefer only a single
or few food types and a generalist will gladly eat many different food
types. Both of the strategies have their advantages and disadvantages.
A specialist may concentrate on a very nutritious food type; when it finds
it favored food, it will be able to obtain most of its nutritional requirements,
but it may have a hard time finding its favored food. A generalist may
be surrounded by many different edible food, but like spinach, it may not
be that good for the organisms, or it may take a long time to process the
food, such as eating barnacles with their hard shells.
Preference: Indication of foods chosen by a predator
given equal access to choices Average population preference study in food
choices of a sea urchin algal abundance avoidance preference Field Diet
**Equal Access to different algae, the sea urchin has preferred and avoided
Food preference in a gastropod with varying food abundances. Nucella % mussels eaten NO SWITCHING % mussels offered Acanthina barnacles food preference mussels SWITCHING relative food abundance *Strong food preferences may prevent food switching regardless of abundance.
Problem, under a given set of circumstances, how should a predator forage? How should a predator respond to variation in environment, such as patchiness of food supply. In such a case, what path should the predator follow.
To solve this problem, ecologists have come up with a model known as the Optimal Foraging Theory, in this model the predator will completely avoid the unprofitable, and completely pursue the profitable.
The model has four assumptions: 1. Foraging behavior is variable, and heritable. 2. Possible responses to prey are constrained 3. Most efficient foragers will be favored by natural selection 4. Efficiency determined by maximizing energy gained in a set amount of time
Two types of consumers are defined by their Energy/Time ratio (E/T).
2. Time Minimizer: Fixed energy goal -minimize time needed to obtain particular energy amount
The foragers face their first dilemma when they must decide
on the quality of the food item it will eat.
Optimal prey is the one where searching time and handling time is minimized
**assume energy is the same, cost is time consumed
Energy Gained VS Time Handling for five prey species E A D
Energy B Gained C
Time required to obtain and handle A--Best prey, most energy gained per unit of timeE--Worst prey, least energy gained per unit of time
Predictions from Model 1. Highest rank prey should always be eaten. 2. Lower rank prey should be pursued and eaten only if this increases net energy gain. Gains>Costs 3. Exception to 2, -Take lower rank prey if recognition time is low low rank prey may be eaten if frequently encountered. 4. Predators should be more selective when prey are abundant and less selective when prey are scarce. Search Time VS Handling Time of Scarce and Abundant Prey scarce prey handling time Time abundant prey A B CPrey Species D E Optimal shifts to the left when a prey species become abundant**assume energy is the same, cost is time consumed
Energy Gained VS Time Obtaining + Handling 5 prey species E D A Energy C Gained B Time required to obtain and handle prey Optimal prey shifts to the right with increasing abundance 5. Inclusion of lower ranked prey is independent of its own abundance and dependant on high ranked prey abundance.
Crab Caranus mearas eating mussel mytilus edulus Optimal size prey?energy obtained/ time spent handlingpreyUnlimited food#eaten/crab/dayLimited Food#eaten/crab/day 1 2 3 4mussel size 5 6cm 1 2 3 4mussel size 5 6cm 1 2 3 4mussel size 5 6cm
** This study shows that the snail will eat the best prey first, and save the lousy prey for last. Inclusion of the lower ranked prey is independent of its abundance and dependant on the abundance of the highest ranked prey.
The foragers second dilemma: How long should a forager stay within a patch? If it stays too long it will be spending too much time for the amount of energy it is accumulating.
Rate of energy extraction Time
Cumulative rate of energy extracted energy extracted predicted time spent in patch t t t t p o TIME assumption- patches all same size, equally spaced
Patch Quality Cumulative average energy high extracted low TIME
**A predator should leave quicker in a low quality patch than in a higher quality patch
Patch Quality Cumulative energy extracted t t t1 t2
**Time spent in a patch increases if travel time is long.
Reproduction is one of the primary goals of any organisms. In order to keep a species from becoming extinct, its members must reproduce at least enough offspring to replace themselves. Organisms invest a considerable amount of time and energy into reproducing. The eggs and sperm they produce are costly cells to make, and their only use is for reproduction. Some organisms also invest a great deal of energy in mate selection and nest preparation. In the case of the higher organisms, parental care may take place, and the organisms will be investing its resources into its offspring for even years to come. If an organism did not have to invest all of this energy into producing and nurturing offspring, they would have more energy available for investing into more complex organs allowing them to possibly be better competitors in its environment. But reproduction is an absolute necessity for organisms that are not immortal, and I do not know any that are. Without reproduction, the species would be gone after just one generation. Reproduction is not necessarily the most important thing to a particular creature, it may be happy to just spend its time swimming and eating, but it is the primary goal of the genes within the creature. The genes (the instructions for creating an organism) are the only level that evolution takes place. Good instructions for creating an organism that is good at reproducing get passed on to further generations. If the instructions were poor, the organism will not reproduce, and the instructions will be lost. Only the good instructions get passed on. Natural selection is very much at work at filtering out successful instructional strategies. One could say that an organism is only the means to continue the flow of genes. That is what natural selection has programmed the genes to do; to creature organisms that deal with the environment well and reproduce. A gene that programmed its organism to be poor at dealing with the environment would probably not be passed on to the next generation. Only those genes that create organisms that are successful in the environment get passed on. This filtering process (natural selection) soon leaves only genes that are good at producing fit organisms. If the environment stayed constant, then evolution would have finished millions of years ago, but the environment is not constant. The genes mutate every once in a few million reproductions. Most of these mutations will be deleterious to the organisms that is created, but some may actually benefit the organisms. Natural selection will work at filtering out the good from the bad mutations. If the mutation is bad, the gene will probably not be passed on (such as a mutation that hindered an organisms ability to eat, the organisms starves to death and does not reproduce). A few of the mutations may actually help the created organisms (such as a gene that allowed for better sight, the organisms may be able to see food that others were missing, or to avoid predation, giving the organisms an advantage). A good mutation would quickly be passed on throughout the species population, and this is evolution! Evolution selects for the best adaptive traits to insure that each female replaces herself within her lifetime, ideally, she should replace herself and then add some.
Evolution selects for the best adaptive traits to insure that each female replaces herself within her lifetime, ideally, she should replace herself and then add some.
Problems in the evolution of life history.
2. How many times should an individual reproduce?
3. How many eggs should there be per clutch?
4. How large should the eggs be?
5. When in the year should reproduction occur?
6. How to locate a mate?
7. How can young locate an appropriate habitat?
Factors influencing the production of maximum number of reproducing offspring.
I. Biology of Individual
1. Planktotrophy: very small and numerous eggs with little yolk. Eggs are of low cost to make, so many can be made. The larvae must feed in plankton column after hatching.
2. Lecithotrophy: relatively large, few, yolky,
and costly eggs. Some nursed. Larvae are non-feeding, simple in form. Found
in plankton, demersal, or benthic environments.
Marine Biology resources by Odyssey Expeditions Tropical Marine Biology Voyages