Download Ecology and Evolution: Principles and Adaptations - Prof. Cagay and more Summaries Life Sciences in PDF only on Docsity!
BIO 107
Ecology Credits: 3 Units Credit Hours: 54 What is Ecology? The study of the interactions between organisms and their environment. Realm of Ecology – Levels of Biological Organization Sub disciplines in Ecology Auto ecology – the interactions between an individual organism and its environment. And it focuses on the physiological response of the individual to the abiotic environment. Population ecology – it examines interactions that occur between a population and its environment. Community ecology – it studies interactions among the populations of all species living in an area at a particular time, which together constitute the community. Sub disciplines in Ecology Ecosystem ecology – the study of the most inclusive interactions, those among all the biotic and abiotic components of the system. An ecosystem thus includes both the community and its physical environment. Physiological ecology – it examines the ways that the bodily processes of organisms are adapted to the physical environment Subdiciplines in Ecology Genetic ecology – the study of the ways in which organism’s ecology shapes its heredity and the ways in which genes influence ecological processes. Systems ecology – it emphasizes mathematical modeling of the interactions among components of an ecological system, particularly the movement of energy and materials among the abiotic and biotic components of an ecosystem. Landscape ecology – it focuses on the spatial patterns of ecological processes. Sciences Allied to Ecology
Natural history – the study of the habits, behaviors, and interactions of organisms in their natural environments. Modern ecologists generally attempt to test an explicit hypothesis. Natural historians tend to focus on the descriptive study of natural phenomena Environmental science – the study of the ecological effects of human activities on the environment. Environmental toxicology – it focuses on the direct ecological effects of pollutants. Conservation biology – it uses the principles of ecology to maintain and manage biological diversity in both relatively natural systems and those more altered by human activity. Subdiciplines in Ecology Wildlife management – the science of the control and manipulation of game and nongame wildlife populations to provide adequate numbers for hunters and other wildlife enthusiasts, as well as to ensure the long-term health of the populations and their habitats The Interaction of Ecology and Evolution Evolution – the genetic change in a population of organisms over time. Ecology and evolution are intimately related because an organism’s ecological situation directs evolution, and the organism’s response to its ecological situation. Adaptation – a genetically determined characteristic (behavioral, morphological, or physiological) that improves an organism’s ability to survive and reproduce in a particular environment. Genetic Variation For any given character, different individuals exhibit different traits. The visible manifestation of a character in an organism is called the phenotype. Variability of traits are the result of differences in the genotype, or genetic constitution, of the individuals being measured, and other traits develop differently among individuals because differences in their environment. The variability among individuals is a result of inherited differences, and some environmentally induced. Fundamentals of Population Genetics
- There must be no net immigration of genotypes into, and no net emigration of genotypes from the population.
- There must be no different mortality or reproduction of the different genotypes.
- There must be no new mutations. Mechanisms of Evolutionary Change
- Genetic Drift – it is the stochastic (random) shifts in allele frequencies. If the population is small, the genotype frequencies expected from Mendel’s laws and the laws of probability may not be achieved. Chance events take on greater importance. Drift occurs in both small and large populations but that the effect is exaggerated in smaller populations. Mechanisms of Evolutionary Change Drift may ultimately result in the complete loss of an allele or its increases to a frequency of 1.0. When several separate populations are undergoing the effects of drift, differences in allele frequencies gradually increase as chance loss and fixation occur in the separate populations. The effects of genetic drift are more pronounced in small populations than in large populations. Mechanisms of Evolutionary Change The key variable in this phenomenon is the effective population size, Ne , which is defined as the number of individuals participating in random mating. Any factor that limits the number of of interbreeding individuals in a population decreases, Ne. Factors that decrease Ne include few males in the population actually mate, fluctuations in population size, variation in the umber of offspring per parent, and overlap of generations; each decreases the actual number of randomly mating individuals relative to the total population size. Mechanisms of Evolutionary Change
- Gene Flow Evolution can also proceed by the loss or gain of alleles via emigration or immigration, a process called gene flow. The movement of alleles can occur by various means.
- Dissemination of plant propagules such as spores and seeds.
- When animals establish themselves in a new population and successfully breed there. Mechanisms of Evolutionary Change
- Natural Selection The differential representation of genotypes in future generations, resulting from heritable differences among them in survival and reproduction. Mechanisms of Evolutionary Change Darwin’s original formulation of the process of evolution by natural selection: a. Inherited variation exists among individuals in the population – not all individuals have the same phenotype. b. Resources are limiting. c. Individuals whose phenotypes make better able to garner scarce resources will, o average, leave more offspring than the other members of the population. Mechanisms of Evolutionary Change The third tenet of Darwin’s arguments leads to the concept of fitness, the relative genetic contribution by an individual’s descendants to future generations. Population geneticists distinguish between fitness measured in absolute and in relative terms. Absolute fitness is the expected number of offspring produced by a particular genotype. This measure incorporates both the survival ability and its fecundity. Relative fitness is based on the relative ability of a genotype to obtain representation in the next generation. Mechanisms of Evolutionary Change Three important properties of fitness
- Fitness is a property of a genotype, not of an individual or a population.
- Fitness is specific to a particular environment.
- Fitness is measured over one generation or more. Modes of Natural Selection
Mimicry Mimicry is the physical resemblance of two or more species resulting from inherent advantages of similar appearance. Batesian mimicry – a benign species resembles a noxious or dangerous one. Mullerian mimicry – the resemblance of several noxious species. Aggressive mimicry – a noxious or dangerous species comes to resemble a benign one. CHAPTER 3 Abiotic Factors and Limits Physical Resources and Limiting Factors Physical resources are those abiotic factors that an organism must assimilate if it is to live and prosper. Plant must assimilate light energy, water, and carbon dioxide if it is to photosynthesize. Animal must consume oxygen and water if it is to survive. Physical factor denotes other kinds of abiotic parameters (such as salinity, pH, or temperature) whose physical or chemical effects may delimit a zone in which life is possible. When factors such as these determine the presence or absence of a species, we refer to them as limiting factors. Two Important Aspects of Physical Resources
- their ecological effects
- their importance as selective forces on organisms. Abiotic factors rarely operate on an organism independently of one another. The importance of the abiotic environment was codified more than 150 years ago. In 1840, the physiologist Justus von Liebeg proposed his law of minimum, which states that the success of an organism is determined by the one crucial ingredient in the environment that is in short supply. The ability of an organism to live and reproduce depends on many abiotic factors. In 1913, Victor Shelford extended this concept by proposing his law of tolerance.
Accordingly, there are upper and lower bounds to the physical factors an organism can tolerate. For example, for any organism there is a maximum temperature that can be tolerated; higher temperature are lethal. Similarly, there is a lower temperature bound, below which life is also impossible. No organism can live everywhere. Tolerance of abiotic conditions can take two nonexclusive forms. The Effects of Abiotic Factors on Species Distribution and Abundance The effects of abiotic factors occur in ecological time – a change in the physical environment manifests itself in effects on the distribution and abundance of the current generation of plants and animals. The range of a species may expand or contract, or the abundance of the species may change locally. Physical Factors that Determine where Species can Live
- Temperature – one of the most important determinants of species distribution
- Water – it also influence the distribution and abundance of many organisms
- Soil salinity – it affects plant distribution In habitats where water is scarce, moisture gradients are likely to have profound effects on plant distribution. In such locales, slight changes in water availability have exaggerated effects on the vegetation. In the deserts of the southern United States, many valleys formed from lakes that dried up at the end of the Pleistocene; salts were concentrated in the basins as the lakes receded. Often a gradient occurs from a relatively nonsaline substrate at higher elevations to highly saline soils in the valley bottoms. Abundance is often greatly reduced in the saltier valley bottoms. Salt marsh habitats provide an example of the combined effects of water and salinity on plant distributions. The zonation of plants in a salt marsh is often determined by the salinity gradient that occurs where freshwater meets seawater.
- Nutritional factors can have important ecological effects.
Other organisms have evolved resistant life cycle stages that are unaffected by temperature extremes. Other animals avoid stressful conditions by migrating to more benign environments. Avoidance Strategies Some organisms’ behavioral adaptations allow them to avoid certain stressful environments by carefully selecting a narrow range of sites that they inhabit or in which they concentrate their activities. The Effects of and Adaptation to Thermal Stress Life on Earth is limited to a remarkably narrow range of temperatures. The temperature range of active life-forms extends from approximately -50 degrees Celsius to near the boiling point of water (100 degrees Celsius). The Effects of Temperature on Organisms As an organism’s temperature increases, death eventually results. The lethal maximum temperature varies widely across taxa and habitats; for some organisms it is as low as 6 degrees Celsius, whereas some bacteria can survive in hot springs above 100 degrees Celsius. High temperatures can have a number of ultimately lethal effects on organisms. Proteins and DNA denature at temperatures above 40 degrees Celsius; the exact temperature depends on the chemical and physical structure of the molecule. An increase in temperature increases the rate of oxygen consumption. If the demand for oxygen outstrips an organism’s ability to supply it to the tissues, death may occur. High temperatures may also disrupt normal cell membrane structure and function. Low temperature may also be lethal. The temperature below which death occurs is as variable across taxa and habitats as upper lethal temperature. Tissues that freeze are in jeopardy. Biochemical processes cease or slow greatly. Ice crystals cause physical damage to membranes and organelles.
For plants, frozen water in the soil is effectively unavailable for uptake by the roots, and death may occur via desiccation. Freezing is not the only cause of death associated with cold temperatures, death apparently results from depression of the respiratory center by low temperature. Principles of Heat Transfer Heat is transferred from one body to another by three processes: conduction, radiation, and evaporation of water. Heat transfer between two objects occurs only if there is a temperature differential between them. Principles of Heat Transfer An organism loses heat to the environment only if its temperature is higher than that of its surroundings, and it gains heat only if its temperature is lower. Conduction is the transfer of heat between two bodies that are in physical contact with one another. Principles of Heat Transfer Conduction is dependent on several factors including each body’s thermal conductivity, the area of contact, and the temperatures of the two bodies. Heat can be transported in fluids by convection, the mass movement of fluids of different temperatures. Principles of Heat Transfer Movement of warm fluid away from the surface of the object causes replacement by cooler fluid, which, in turn, is heated and also moves away. Radiation is the transfer of heat between two objects that are not in physical contact. Principles of Heat Transfer Any object with a temperature above absolute zero Kelvin emits electromagnetic radiation, which can pass through a vacuum. The temperature of the surface is very important in determining the rate of emission. The emissivity of an object is its propensity to emit radiation; absorptivity is its tendency to absorb the radiation that strikes it. Principles of Heat Transfer
The metabolic rate remains essentially constant over a range of ambient temperatures referred to as the thermal neutral zone. Homeothermy and Poikilothermy At temperature below the lower critical temperature, energy must be expended to maintain body temperature. Adaptations to Hot Environments The two primary modes of evaporative water loss in animals are panting and sweating. Mammals (carnivores) coll by panting. One advantage of panting is that animal facilitates evaporation by generating air flow over the moist nasal and oral surfaces. Adaptations to Hot Environments One disadvantage is that the excess respiration associated with panting can deplete the lungs of carbon dioxide, and its loss can leave the blood excessively alkaline. Panting requires muscular movement and thus involves the expenditure of energy. Adaptations to Hot Environments The elasticity of the respiratory tract greatly reduces the energetic cost of panting. Bird also pant to regulate their temperature and they increase evaporation by rapid oscillations of portions of the throat, an action called gular fluttering. Adaptations to Hot Environments Sweating is common in humans and in many ungulates, including horses, cattle, sheep, goats, and some antelope. Even in heavily furred mammals such as the camel, sweating is an effective heat loss mechanism because the dry desert air facilitates rapid evaporation. A few homeotherms are able to inhabit very hot environments because of their ability to store heat. Adaptations to Cold Environments Increasing internal heat production and decreasing heat loss via conduction and radiation are the most important processes for animals in the cold. Adaptations to Cold Environments
One option that accounts for much of the increase in metabolic rate at temperatures below the thermal neutral zone is increased heat production by the animal. Muscular activity, exercise, and shivering contribute to metabolic heat production. Adaptations to Cold Environments In nonshivering thermogenesis, animals store energy in the form of brown fat. This adipose tissue is high in cytochrome c and can consume oxygen at a high rate, making it useful in the generation of heat. Adaptations to Cold Environments Increasing insulation by decreasing conductance is another strategy for maintaining high body temperatures in cold regions. Fur is an excellent insulator whose value for that purpose increases linearly with thickness. Layers of subcutaneous fat constitute important insulation. Adaptations to Cold Environments Another adaptive option suggested by the heat balance equation is adjustment of radiative heat loss. Radiative heat loss is proportional to the size of the radiative surface, one morphological adaptation available to an animal in a cold habitats is to reduce the relative size of its surface area. Adaptations to Cold Environments Radiative heat loss works in two ways: body shape and body size. Animals in cold environment tend to have bodies and extremities that are thick and stock. Animals in hot environments are more slender, with longer, thinner extremities that increase the relative surface area and facilitate radiative heat loss. Adaptations to Cold Environments Body size also affects the radiative heat loss. Heat production is proportional to body mass whereas radiative heat loss is proportional to surface area. Small animal will have a higher surface-to-volume ratio than a large animal.
Migration is also a means of avoiding temperature extremes. Migration is inextricably linked to avoiding energy shortages associated with winter. Plant Adaptation to Thermal Stress Plants are incapable of fleeing temperature extremes; options such as behavioral thermoregulation and migration are unavailable to them. Plants can face thermal stress by maintaining temperature differentials between their tissues and the environment. Plant Adaptation to Thermal Stress The temperature of shoots and leaves may differ markedly from the ambient temperature. If they are in direct sunlight, their temperature may be several degrees higher than the air temperature. If they are transpiring rapidly, evaporative water loss may decrease plant temperatures relative to ambient temperature. Plant Adaptation to Thermal Stress The thickness of leaves can also be an important and adaptive temperature modulator. Thick leaves can be as much as 30 degrees Celsius than the air, thin leaves 15 degrees Celsius cooler. The presence of small hairs on the plant surface modulates tissue temperatures by trapping a layer of air that buffers the plant from changes in air temperature. ADAPTATION FOR WATER BALANCE Water is essential for all life and it is the most crucial limiting abiotic factors. Water plays a key role in many metabolic pathways. All organisms must have sufficient amounts of water available to carry out their life functions. The Physiological Ecology of Water Water have profound effects on its role in physiological and ecological processes because of its unique chemical and physical properties. (1) Water always contains gases, salts, and other compounds in solution. (2) Water has both an extremely high heat capacity and a high heat of vaporization.
The Physiological Ecology of Water (3) Water molecules are polar thus it is cohesive. The cohesive propety of water plays an important physiological ecology of water balance in plants because it provides a mechanism by which water across can be drawn up the vascular tissue of plants. The Physiological Ecology of Water Osmotic effects are one of the most important aspects of the physiological ecology of water. Osmosis is the movement of water across a semipermeable membrane in relation to solute concentration. Water flows from regions of lower solute concentration to regions of higher solute concentration. The Physiological Ecology of Water If the internal contents of an organism are more concentrated than the medium in which it lives, then it is hypertonic relative to its medium. If the internal contents are less concentrated than the medium, then the organism is hypotonic relative to its medium. The Physiological Ecology of Water In a highly saline environment, the organism is hypotonic. Water will tend to flow from the tissues of organism. In a low-salinity environment, water will tend to flow into the organism. In both cases, there must be physiological adaptations to modify these flows. The Physiological Ecology of Water Organisms that can tolerate variation in the salt content of the water they inhabit are termed euryhaline : organisms that require a narrow range of salt concentrations are stenohaline. The Physiological Ecology of Water Species respond to the osmotic problems presented by salt concentrations in two general ways. (1) Osmoconformers if they allow the osmotic conditions of their tissues to change in response to the environment.
(1) Hagfish which are hypertonic or isotonic relative to seawater. These animals experience little osmotic flow into or out of their tissues. Animal Adaptations for Water Balance (2) Teleost fishes that are hypotonic relative to seawater, drink seawater to counteract the inevitable loss of water from their tissues. Active transport is required to move the salts against the concentration gradient from the tissue to the seawater. Animal Adaptations for Water Balance Freshwater animals face different set of problems. Because the tissues of these organisms are hypertonic relative to their surroundings, the animals tend to gain water from the environment. Animal Adaptations for Water Balance Freshwater teleost have evolved a set of adaptations to cope these problems. (1) They eliminate large volumes of high a highly dilute urine, excreting up to 1/3 of their body weight in water each day. (2) Their gills actively transport ions from the water into the body to accommodate the loss of certain critical ions caused by the tremendous rate of urine excretion. Animal Adaptations for Water Balance Aside from excretion, terrestrial animals losses water by means of evaporation. Evaporation occurs through respiration or directly from the body surface if the organism sweats or has a water-permeable exterior. Animal Adaptations for Water Balance Other animals evolved integuments that are impervious to water to reduce the rate of evaporation; the keratinized skin of reptiles and the chitinous exoskeleton that covers many invertebrates are two examples. Animal Adaptations for Water Balance Some animals adopt behavioral strategies, such as nocturnality. Fossorial animals such as moles and gophers live underground in burrow systems in which the relative humidity is so high that evaporation is greatly reduced. Animal Adaptations for Water Balance
Some mammals and birds reduce evaporative water loss by recovering moisture from the air they exhale from the lungs. The other major source of water loss for terrestrial animals is urine and feces. Desert animals generally have long digestive tracts that absorb as much water from the feces as possible before it is excreted. Plant Adaptation for Water Balance Plants absorb water primarily via roots. The important factors in determining the water intake of a plant are the amount and availability of water in the soil and it also depends on the nature and size of the soil particles and on the osmotic environment. Plant Adaptation for Water Balance Root morphology and physiology constitute an important set of adaptations that determine a plant’s water requirements. Plants in dry environments are called xerophytes and can adopt one of two strategies to ensure that they obtain sufficient water. Plant Adaptation for Water Balance (1) Some produce taproots that penetrate deep into the soil, where they pick up water pulled to lower strata by gravity. (2) Others, like the grasses, produce highly branched, shallow, fibrous roots. Plant Adaptation for Water Balance Having many highly branched roots near the surface accomplishes two things for a plant. (1) It helps ensure that the root will locate a region of soil that contains moisture above the permanent wilting point. (2) The plants has the opportunity to capture water soon after it reaches the ground-before it can evaporate and before other plants absorb it. Plant Adaptation for Water Balance In the leaves and stems, loss of internal water occurs by evaporation. Most plants have a waxy covering on the surface of the leaves and stems, called the cuticle, that reduces the evaporative loss of water directly from the plant tissues.
