DOCSLIB.ORG

Community Ecology 54

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Community Ecology 54 Community ecology 54 Figure 54.1 Which species benefits from this interaction? Key ConCepts Communities in Motion At first glance, you might think the situation looks dire for this bluestreak cleaner 54.1 Community interactions are classified by whether they help, wrasse, which has ventured into the mouth of the giant moray eel, a voracious preda- harm, or have no effect on the tor in its coral reef habitat (Figure 54.1). With one snap of its jaw, the eel could easily species involved crush the fish and swallow it. However, the wrasse is not in danger of becoming this 54.2 Diversity and trophic structure eel’s dinner. The much larger animal remains still, with its mouth open, and allows characterize biological the smaller fish free passage as it picks out and eats tiny parasites living inside the eel’s communities mouth and on its skin. 54.3 Disturbance influences species In this interaction, both organisms benefit: The cleaner wrasse gains access to a diversity and composition supply of food, and its moray eel client is freed of parasites that might weaken it or spread disease. There are many other examples of such mutually beneficial “cleaner” 54.4 Biogeographic factors affect community diversity and “client” relationships in marine habitats, such as the cleaner shrimp and eel interaction shown below. However, other interactions between species are less benign 54.5 Pathogens alter community for one of the participants, and still other interactions can negatively affect the repro- structure locally and globally duction and survival of both species involved. In Chapter 53, you learned how individuals within a population can affect other individuals of the same species. This chapter will examine ecological interactions between populations of different species. A group of populations of different spe- cies living in close enough proximity to interact is called a biological community. When you see this blue icon, log in to MasteringBiology Get Ready for This Chapter and go to the Study Area for digital resources. Ecologists define the boundaries of a particular community supply on land; most terrestrial species use this resource but to fit their research questions: They might study the com- do not usually compete for it. munity of decomposers and other organisms living on a rotting log, the benthic community in Lake Superior, or the Competitive Exclusion community of trees and shrubs in Sequoia National Park in What happens in a community when two species compete for California. limited resources? In 1934, Russian ecologist G. F. Gause stud- We begin this chapter by exploring the kinds of interac- ied this question using laboratory experiments with two closely tions that occur between species in a community, such as related ciliate species, Paramecium aurelia and Paramecium the cleaner wrasse and eel in Figure 54.1. We’ll then consider caudatum (see Figure 28.17a). He cultured the species under several of the factors that are most significant in structuring stable conditions, adding a constant amount of food each day. a community—in determining how many species there are, When Gause grew the two species separately, each population which particular species are present, and the relative abun- increased rapidly in number and then leveled off at the appar- dance of these species. Finally, we’ll apply some of the prin- ent carrying capacity of the culture (see Figure 53.11a for an ciples of community ecology to the study of human disease. illustration of the logistic growth of a Paramecium population). But when Gause grew the two species together, P. caudatum became extinct in the culture. Gause inferred that P. aurelia ConCept 54.1 had a competitive edge in obtaining food. More generally, his Community interactions results led him to conclude that two species competing for the are classified by whether they same limiting resources cannot coexist permanently in the help, harm, or have no effect same place. In the absence of disturbance, one species will use the resources more efficiently and reproduce more rapidly than on the species involved the other. Even a slight reproductive advantage will eventually Some key relationships in the life of an organism are its inter- lead to local elimination of the inferior competitor, an outcome actions with individuals of other species in the community. called competitive exclusion. These interspecific interactions include competition, predation, herbivory, parasitism, mutualism, and commen- Ecological Niches and Natural Selection salism. In this section, we’ll define and describe each of these evolution Competition for limited resources can cause interactions, grouping them according to whether they have evolutionary change in populations. One way to examine positive (+) or negative (-) effects on the survival and repro- how this occurs is to focus on an organism’s ecological duction of each of the two species engaged in the interaction. niche, the specific set of biotic and abiotic resources that For example, predation is a +/- interaction, with a positive an organism uses in its environment. The niche of a tropical effect on the predator population and a negative effect on the tree lizard, for instance, includes the temperature range it prey population. Mutualism is a +/+ interaction because the tolerates, the size of branches on which it perches, the time survival and reproduction of both species are increased in the of day when it is active, and the sizes and kinds of insects presence of the other. A 0 indicates that a species is not affected it eats. Such factors define the lizard’s niche, or ecological by the interaction in any known way. We’ll consider three role—how it fits into an ecosystem. broad categories of ecological interactions: competition (-/-), We can use the niche concept to restate the principle of exploitation (+/-), and positive interactions (+/+ or +/0). competitive exclusion: Two species cannot coexist perma- Historically, most ecological research has focused on inter- nently in a community if their niches are identical. However, actions that have a negative effect on at least one species, such ecologically similar species can coexist in a community if one as competition and predation. As we’ll see, however, positive or more significant differences in their niches arise through interactions are ubiquitous and have major effects on commu- time. Evolution by natural selection can result in one of the nity structure. species using a different set of resources or similar resources at different times of the day or year. The differentiation of niches that enables similar species to coexist in a community Competition is a -/- interaction that occurs when indi- is called resource partitioning (Figure 54.2). viduals of different species compete for a resource that limits As a result of competition, a species’ fundamental niche, the survival and reproduction of each species. Weeds grow- which is the niche potentially occupied by that species, is ing in a garden compete with garden plants for soil nutrients often different from its realized niche, the portion of its fun- and water. Lynx and foxes in the northern forests of Alaska damental niche that it actually occupies. Ecologists can iden- and Canada compete for prey such as snowshoe hares. In tify the fundamental niche of a species by testing the range contrast, some resources, such as oxygen, are rarely in short of conditions in which it grows and reproduces in the absence chApter 54 Community Ecology 1213 Figure 54.2 Resource partitioning among Dominican Figure 54.3 Republic lizards. Seven species of Anolis lizards live in close proximity, inquiry Can a species’ niche be influenced and all feed on insects and other small arthropods. However, competition for food is reduced because each lizard species has a different preferred by interspecific competition? perch, thus occupying a distinct niche. experiment Ecologist Joseph Connell studied two barnacle species— A. distichus perches A. insolitus usually perches Chthamalus stellatus and Balanus balanoides—that have a stratified on fence posts and on shady branches. distribution on rocks along the coast of Scotland. Chthamalus is usually other sunny surfaces. found higher on the rocks than Balanus. To determine whether the distribution of Chthamalus is the result of interspecific competition with Balanus, Connell removed Balanus from the rocks at several sites. High tide Chthamalus A. ricordii Balanus Chthamalus realized niche Balanus realized niche A. insolitus Ocean Low tide A. aliniger A. christophei A. distichus Results Chthamalus spread into the A. cybotes region formerly occupied by Balanus. High tide A. etheridgei Chthamalus fundamental niche of competitors. They can also test whether a potential competi- tor limits a species’ realized niche by removing the competitor and seeing if the first species expands into the newly available Ocean Low tide space. The classic experiment depicted in Figure 54.3 clearly showed that competition between two barnacle species kept Conclusion Interspecific competition makes the realized niche of one species from occupying part of its fundamental niche. Chthamalus much smaller than its fundamental niche. Species can partition their niches not just in space, as Data from J. H. Connell, The influence of interspecific competition and other factors lizards and barnacles do, but in time as well. The common on the distribution of the barnacle Chthamalus stellatus, Ecology 42:710–723 (1961). spiny mouse (Acomys cahirinus) and the golden spiny mouse Instructors: A related experimental inquiry tutorial (A. russatus) live in rocky habitats of the Middle East and can be assigned in MasteringBiology. Africa, sharing similar microhabitats and food sources. Where WHAt iF? Other observations showed that Balanus cannot survive high on they coexist, A. cahirinus is nocturnal (active at night), while the rocks because it dries out during low tides. How would Balanus’s realized niche compare with its fundamental niche? A. russatus is diurnal (active during the day). Surprisingly, laboratory research showed that A.
Load more

Recommended publications
  • Biogeography, Community Structure and Biological Habitat Types of Subtidal Reefs on the South Island West Coast, New Zealand
    Biogeography, community structure and biological habitat types of subtidal reefs on the South Island West Coast, New Zealand SCIENCE FOR CONSERVATION 281 Biogeography, community structure and biological habitat types of subtidal reefs on the South Island West Coast, New Zealand Nick T. Shears SCIENCE FOR CONSERVATION 281 Published by Science & Technical Publishing Department of Conservation PO Box 10420, The Terrace Wellington 6143, New Zealand Cover: Shallow mixed turfing algal assemblage near Moeraki River, South Westland (2 m depth). Dominant species include Plocamium spp. (yellow-red), Echinothamnium sp. (dark brown), Lophurella hookeriana (green), and Glossophora kunthii (top right). Photo: N.T. Shears Science for Conservation is a scientific monograph series presenting research funded by New Zealand Department of Conservation (DOC). Manuscripts are internally and externally peer-reviewed; resulting publications are considered part of the formal international scientific literature. Individual copies are printed, and are also available from the departmental website in pdf form. Titles are listed in our catalogue on the website, refer www.doc.govt.nz under Publications, then Science & technical. © Copyright December 2007, New Zealand Department of Conservation ISSN 1173–2946 (hardcopy) ISSN 1177–9241 (web PDF) ISBN 978–0–478–14354–6 (hardcopy) ISBN 978–0–478–14355–3 (web PDF) This report was prepared for publication by Science & Technical Publishing; editing and layout by Lynette Clelland. Publication was approved by the Chief Scientist (Research, Development & Improvement Division), Department of Conservation, Wellington, New Zealand. In the interest of forest conservation, we support paperless electronic publishing. When printing, recycled paper is used wherever possible. CONTENTS Abstract 5 1. Introduction 6 2.
    [Show full text]
  • Functional Benefits of Predator Species Diversity Depend on Prey Identity
    Ecological Entomology (2005) 30, 497–501 Functional benefits of predator species diversity depend on prey identity A. WILBY1 , S. C. VILLAREAL2 ,L.P.LAN3 ,K.L.HEONG2 and 1 M. B. THOMAS 1Department of Agricultural Sciences and NERC Centre for Population Biology, Imperial College London, U.K., 2International Rice Research Institute, Metro Manila, Philippines and 3Institute of Agricultural Sciences of South Vietnam, Ho Chi Minh City, Vietnam Abstract. 1. Determining the functional significance of species diversity in nat- ural enemy assemblages is a key step towards prediction of the likely impact of biodiversity loss on natural pest control processes. While the biological control literature contains examples in which increased natural enemy diversity hinders pest control, other studies have highlighted mechanisms where pest suppression is promoted by increased enemy diversity. 2. This study aimed to test whether increased predator species diversity results in higher rates of predation on two key, but contrasting, insect pest species commonly found in the rice ecosystems of south-east Asia. 3. Glasshouse experiments were undertaken in which four life stages of a planthopper (Nilaparvata lugens) and a moth (Marasmia patnalis) were caged with single or three-species combinations of generalist predators. 4. Generally, predation rates of the three-species assemblages exceeded expec- tation when attacking M. patnalis, but not when attacking N. lugens. In addition, a positive effect of increased predator species richness on overall predation rate was found with M. patnalis but not with N. lugens. 5. The results are consistent with theoretical predictions that morphological and behavioural differentiation among prey life stages promotes functional com- plementarity among predator species.
    [Show full text]
  • MS-LS2-1 Ecosystems: Interactions, Energy, and Dynamics
    MS-LS2-1 Ecosystems: Interactions, Energy, and Dynamics Students who demonstrate understanding can: MS-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem. [Clarification Statement: Emphasis is on cause and effect relationships between resources and growth of individual organisms and the numbers of organisms in ecosystems during periods of abundant and scarce resources.] The performance expectation above was developed using the following elements from the NRC document A Framework for K-12 Science Education: Science and Engineering Disciplinary Core Ideas Crosscutting Concepts Practices LS2.A: Interdependent Relationships Cause and Effect in Ecosystems Analyzing and Interpreting Data Cause and effect relationships Analyzing data in 6–8 builds on K–5 Organisms, and populations of may be used to predict experiences and progresses to organisms, are dependent on their phenomena in natural or designed extending quantitative analysis to environmental interactions both with systems. other living things and with nonliving investigations, distinguishing between correlation and causation, and basic factors. statistical techniques of data and error In any ecosystem, organisms and analysis. populations with similar requirements Analyze and interpret data to for food, water, oxygen, or other provide evidence for phenomena. resources may compete with each other for limited resources, access to which consequently constrains their growth and reproduction. Growth of organisms and population increases are limited by access to resources. Observable features of the student performance by the end of the course: 1 Organizing data a Students organize the given data (e.g., using tables, graphs, and charts) to allow for analysis and interpretation of relationships between resource availability and organisms in an ecosystem, including: i.
    [Show full text]
  • Genetic Methods for Estimating the Effective Size of Cetacean Populations
    Genetic Methods for Estimating the Effective Size of Cetacean Populations Robin S. Waples Northwest Fisheries Center, National Marine Fisheries Service, 2725 Montlake Boulevard East, Seattle, Washington 98112, USA ABSTRACT Some indirect (genetic) methods for estimating effective population size (N,) are evaluated for their suitability in studyingcetacean populations. The methodscan be grouped into those that (1) estimate current N,, (2) estimate long-term N, and (3) provide information about recent genetic bottlenecks. The methods that estimate current effective size are best suited for the analysis of small populations. and nonrandom sampling and population subdivision are probably the most serious sources of potential bias. Methods that estimate long-term N, are best suited to the analysis of large populations or entire species, may be more strongly influenced by natural selection and depend on accurate estimates of mutation or DNA base substitution rates. Precision of the estimates of N, is likely to be a limiting factor in many applications of the indirect methods. Keywords: genetics; assessment: cetaceans - general: evolution. INTRODUCTION Population size is one of the most important factors that determine the rate of various evolutionary processes, and it appears as a parameter in many of the fundamental equations of population genetics. However, knowledge merely of the total number of individuals (N) in a population is not sufficient for an accurate description of these evolutionary processes. Because of the influence of demographic parameters, two populations of the same total size may experience very different rates of genetic change. Wright (1931; 1938) developed the concept of effective population size (N,) as a way of summarising relevant demographic information so that one can predict the evolutionary consequences of finite population size (see Fig.
    [Show full text]
  • Species Richness, Species–Area Curves and Simpson's Paradox
    Evolutionary Ecology Research, 2000, 2: 791–802 Species richness, species–area curves and Simpson’s paradox Samuel M. Scheiner,1* Stephen B. Cox,2 Michael Willig,2 Gary G. Mittelbach,3 Craig Osenberg4 and Michael Kaspari5 1Department of Life Sciences (2352), Arizona State University West, P.O. Box 37100, Phoenix, AZ 85069, 2Program in Ecology and Conservation Biology, Department of Biological Sciences and The Museum, Texas Tech University, Lubbock, TX 79409, 3W.K. Kellogg Biological Station, 3700 E. Gull Lake Drive, Michigan State University, Hickory Corners, MI 49060, 4Department of Zoology, University of Florida, Gainesville, FL 32611 and 5Department of Zoology, University of Oklahoma, Norman, OK 73019, USA ABSTRACT A key issue in ecology is how patterns of species diversity differ as a function of scale. The scaling function is the species–area curve. The form of the species–area curve results from patterns of environmental heterogeneity and species dispersal, and may be system-specific. A central concern is how, for a given set of species, the species–area curve varies with respect to a third variable, such as latitude or productivity. Critical is whether the relationship is scale-invariant (i.e. the species–area curves for different levels of the third variable are parallel), rank-invariant (i.e. the curves are non-parallel, but non-crossing within the scales of interest) or neither, in which case the qualitative relationship is scale-dependent. This recognition is critical for the development and testing of theories explaining patterns of species richness because different theories have mechanistic bases at different scales of action.
    [Show full text]
  • Loss of Microsatellite Diversity and Low Effective Population Size in an Overexploited Population of New Zealand Snapper (Pagrus Auratus)
    Loss of microsatellite diversity and low effective population size in an overexploited population of New Zealand snapper (Pagrus auratus) Lorenz Hauser*†, Greg J. Adcock*‡, Peter J. Smith§, Julio H. Bernal Ramı´rez*¶, and Gary R. Carvalho* *Molecular Ecology and Fisheries Genetics Laboratory, Department of Biological Sciences, University of Hull, Hull HU6 7RX, United Kingdom; and §National Institute of Water and Atmospheric Research, P.O. Box 14901, Wellington, New Zealand Edited by John C. Avise, University of Georgia, Athens, GA, and approved June 27, 2002 (received for review April 23, 2002) Although the effects of overfishing on species diversity and abun- ered being in danger of losing genetic diversity (8), and so there dance are well documented, threats to the genetic diversity of appears to be little cause for concern from a genetic perspective. marine fish populations have so far been largely neglected. Indeed, On the other hand, the number of fish in a population (census there seems to be little cause for concern, as even ‘‘collapsed’’ population size, N) is often much larger than the genetically stocks usually consist of several million individuals, whereas pop- effective population size (Ne), which determines the genetic ulation genetics theory suggests that only very small populations properties of a population (12). The long-term evolutionary Ne suffer significant loss of genetic diversity. On the other hand, in is often orders of magnitude smaller than current population many marine species the genetically effective population size (Ne), sizes, probably because of historic population bottlenecks, ‘‘se- which determines the genetic properties of a population, may be lective sweeps,’’ or colonization histories (13).
    [Show full text]
  • European Gradients of Resilience in the Face of Climate Extremes
    EUROPEAN GRADIENTS OF RESILIENCE IN THE FACE OF CLIMATE EXTREMES POLICY BRIEF Field site in Belgium with rainout shelters deployed in 2013 ©Sigi Berwaers This policy brief is based on the results Extreme weather events and the presence of invasive species can act as of the BiodivERsA-funded project pressures threatening biodiversity, resilience and ecosystem services of semi- ‘SIGNAL’ addressing the interaction of three major research areas, combined natural grasslands and drive them beyond thresholds of system integrity in ecology for the first time: biodiversity (tipping points and regime shifts). On the other hand, biodiversity itself may experiments, climate change research, and invasion research. The project made use buffer ecosystem functioning and services against change. Potential stabilising of coordinated experiments in different mechanisms include species richness, presence of key species such as legumes climates across Europe, thereby increasing and within-species diversity. These potential buffers can be promoted by the scope and relevance of the results. conservation management and policy adjustments. K EY POLICY RECOMMENDATIONS • Local biodiversity should be actively stimulated or preserved across European grasslands in order to increase the stability of ecosystem service provisioning, which is especially relevant as climate extremes are expected to become more frequent and intense. • Adjustment of mowing frequency and cutting height can help maintain or increase biodiversity. • More explicit consideration of within-species diversity is warranted, as this component of biodiversity can contribute to stabilising ecosystem functioning in the face of climate extremes. • Ecosystem responses to climate extremes of similar magnitude can vary significantly between climates and regions, suggesting that targeted policy requires tailor-made impact predictions.
    [Show full text]
  • Ecological Principles and Function of Natural Ecosystems by Professor Michel RICARD
    Intensive Programme on Education for sustainable development in Protected Areas Amfissa, Greece, July 2014 ------------------------------------------------------------------------ Ecological principles and function of natural ecosystems By Professor Michel RICARD Summary 1. Hierarchy of living world 2. What is Ecology 3. The Biosphere - Lithosphere - Hydrosphere - Atmosphere 4. What is an ecosystem - Ecozone - Biome - Ecosystem - Ecological community - Habitat/biotope - Ecotone - Niche 5. Biological classification 6. Ecosystem processes - Radiation: heat, temperature and light - Primary production - Secondary production - Food web and trophic levels - Trophic cascade and ecology flow 7. Population ecology and population dynamics 8. Disturbance and resilience - Human impacts on resilience 9. Nutrient cycle, decomposition and mineralization - Nutrient cycle - Decomposition 10. Ecological amplitude 11. Ecology, environmental influences, biological interactions 12. Biodiversity 13. Environmental degradation - Water resources degradation - Climate change - Nutrient pollution - Eutrophication - Other examples of environmental degradation M. Ricard: Summer courses, Amfissa July 2014 1 1. Hierarchy of living world The larger objective of ecology is to understand the nature of environmental influences on individual organisms, populations, communities and ultimately at the level of the biosphere. If ecologists can achieve an understanding of these relationships, they will be well placed to contribute to the development of systems by which humans
    [Show full text]
  • Community Ecology
    Schueller 509: Lecture 12 Community ecology 1. The birds of Guam – e.g. of community interactions 2. What is a community? 3. What can we measure about whole communities? An ecology mystery story If birds on Guam are declining due to… • hunting, then bird populations will be larger on military land where hunting is strictly prohibited. • habitat loss, then the amount of land cleared should be negatively correlated with bird numbers. • competition with introduced black drongo birds, then….prediction? • ……. come up with a different hypothesis and matching prediction! $3 million/yr Why not profitable hunting instead? (Worked for the passenger pigeon: “It was the demographic nightmare of overkill and impaired reproduction. If you’re killing a species far faster than they can reproduce, the end is a mathematical certainty.” http://www.audubon.org/magazine/may-june- 2014/why-passenger-pigeon-went-extinct) Community-wide effects of loss of birds Schueller 509: Lecture 12 Community ecology 1. The birds of Guam – e.g. of community interactions 2. What is a community? 3. What can we measure about whole communities? What is an ecological community? Community Ecology • Collection of populations of different species that occupy a given area. What is a community? e.g. Microbial community of one human “YOUR SKIN HARBORS whole swarming civilizations. Your lips are a zoo teeming with well- fed creatures. In your mouth lives a microbiome so dense —that if you decided to name one organism every second (You’re Barbara, You’re Bob, You’re Brenda), you’d likely need fifty lifetimes to name them all.
    [Show full text]
  • Islands in the Stream 2002: Exploring Underwater Oases
    Islands in the Stream 2002: Exploring Underwater Oases NOAA: Office of Ocean Exploration Mission Three: SUMMARY Discovery of New Resources with Pharmaceutical Potential (Pharmaceutical Discovery) Exploration of Vision and Bioluminescence in Deep-sea Benthos (Vision and Bioluminescence) Microscopic view of a Pachastrellidae sponge (front) and an example of benthic bioluminescence (back). August 16 - August 31, 2002 Shirley Pomponi, Co-Chief Scientist Tammy Frank, Co-Chief Scientist John Reed, Co-Chief Scientist Edie Widder, Co-Chief Scientist Pharmaceutical Discovery Vision and Bioluminescence Harbor Branch Oceanographic Institution Harbor Branch Oceanographic Institution ABSTRACT Harbor Branch Oceanographic Institution (HBOI) scientists continued their cutting-edge exploration searching for untapped sources of new drugs, examining the visual physiology of deep-sea benthos and characterizing the habitat in the South Atlantic Bight aboard the R/V Seaward Johnson from August 16-31, 2002. Over a half-dozen new species of sponges were recorded, which may provide scientists with information leading to the development of compounds used to study, treat, or diagnose human diseases. In addition, wondrous examples of bioluminescence and emission spectra were recorded, providing scientists with more data to help them understand how benthic organisms visualize their environment. New and creative Table of Contents ways to outreach and educate the public also Key Findings and Outcomes................................2 Rationale and Objectives ....................................4
    [Show full text]
  • Improving Habitat and Connectivity Model Predictions with Multi-Scale Resource Selection Functions from Two Geographic Areas
    Landscape Ecol (2019) 34:503–519 https://doi.org/10.1007/s10980-019-00788-w (0123456789().,-volV)(0123456789().,-volV) RESEARCH ARTICLE Improving habitat and connectivity model predictions with multi-scale resource selection functions from two geographic areas Ho Yi Wan . Samuel A. Cushman . Joseph L. Ganey Received: 22 May 2018 / Accepted: 18 February 2019 / Published online: 4 March 2019 Ó This is a U.S. government work and its text is not subject to copyright protection in the United States; however, its text may be subject to foreign copyright protection 2019 Abstract converted the models into landscape resistance sur- Context Habitat loss and fragmentation are the most faces and used simulations to model connectivity pressing threats to biodiversity, yet assessing their corridors for the species, and created composite impacts across broad landscapes is challenging. habitat and connectivity models by averaging the Information on habitat suitability is sometimes avail- local and non-local models. able in the form of a resource selection function model Results While the local and the non-local models developed from a different geographical area, but its both performed well, the local model performed best applicability is unknown until tested. in the part of the study area where it was built, but Objectives We used the Mexican spotted owl as a performed worse in areas that are beyond the extent of case study to demonstrate how models developed from the data used to train it. The composite habitat model different geographic areas affect our predictions for improved performances over both models in most habitat suitability, landscape resistance, and connec- cases.
    [Show full text]
  • Interactions Between Organisms . and Environment
    INTERACTIONS BETWEEN ORGANISMS . AND ENVIRONMENT 2·1 FUNCTIONAL RELATIONSHIPS An understanding of the relationships between an organism and its environment can be attained only when the environmental factors that can be experienced by the organism are considered. This is difficult because it is first necessary for the ecologist to have some knowledge of the neurological and physiological detection abilities of the organism. Sound, for example, should be measured with an instrument that responds to sound energy in the same way that the organism being studied does. Snow depths should be measured in a manner that reflects their effect on the animal. If six inches of snow has no more effect on an animal than three inches, a distinction between the two depths is meaningless. Six inches is not twice three inches in terms of its effect on the animal! Lower animals differ from man in their response to environmental stimuli. Color vision, for example, is characteristic of man, monkeys, apes, most birds, some domesticated animals, squirrels, and, undoubtedly, others. Deer and other wild ungulates probably detect only shades of grey. Until definite data are ob­ tained on the nature of color vision in an animal, any measurement based on color distinctions could be misleading. Infrared energy given off by any object warmer than absolute zero (-273°C) is detected by thermal receptors on some animals. Ticks are sensitive to infrared radiation, and pit vipers detect warm prey with thermal receptors located on the anterior dorsal portion of the skull. Man can detect different levels of infrared radiation with receptors on the skin, but they are not directional nor are they as sensitive as those of ticks and vipers.
    [Show full text]