Ecology : An Introduction

By

Feliciano G. Calora Jr., PhDAssociate Professor

College of Forestry,

Benguet State University

ECOLOGY

The study of the interactions between organisms and their environment. The environment is a combination of the physical environment (temperature, water available, etc) and any influences on an organism exerted by other organisms – the biotic environment

• Ecology can be considered on a wide scale, moving from an individual molecule to the entire global ecosystem, however four (4) identifiable subdivisions of scale are of particular interest

•INDIVIDUALS

•POPULATIONS

•COMMUNTIES

•ECOSYSTEMS

•At the INDIVIDUAL level, the response of individuals to their environment (biotic and abiotic) is the key issue

•At the POPULATION level of a single species, the determinants of abundance and population fluctuations dominate

• COMMUNITIES are the mixture of populations of different species in a defined area

•ECOSYSTEMS comprise the biotic community in conjunction with the associated complex of physical factors that characterize the physical environment.

Ten Rules of Ecology

• Ecology is a Science - this is a scientific discipline which aims to understand the relationships between organisms and their wide environment.

• Ecology is only understandable in the light of Evolution – the huge diversity of organisms and the wealth of variety in their morphologies, physiologies and behavior are all the result of many millions of years of evolution.

Ten Rules of Ecology

3. Nothing happens for the “good of the species” - a common misconception is the notion that patterns of behavior in organisms which appear to be costly to an individual are for the good of the species. Natural selection will favor those genes which are assessed on to the most offspring. If the genes for suicidal behavior in ants or early death in octopuses were good for the species but bad for the individuals carrying them, evolution would favor their replacement with other genes.

Ten Rules of Ecology• Genes and Environment are both important –

environmental conditions will define the birth rate, growth rate and level of mortality of a species. The genes which define an organisms make-up are also of fundamental importance. The emergent phenotype of an organism is a joint product of genetic code and the environmental stimuli

• Understanding complexity requires Models – at first glance ecology might appear incomprehensible , millions of species each with varying numbers and ever changing behaviors set in the context of a structurally complex and dynamic environment. These can be understood thru models e.g. mathematical model

Ten Rules of Ecology

6. Story-telling is Dangerous – in attempting to explain ecological patterns or relationships, it is easy to slip into a make-believe world where every observation is readily explained by some ad hoc assertion such as the classic “examination blunder” – polar bears are white so they are hidden from predators in the snow

7. There are Hierarchies of explanations – For any observation there is always an immediate cause that can be diagnosed. Often the causal explanation is insufficiently informative and we need to probe deeper to reach a fuller grasp of the situation

Ten Rules of Ecology.

8. There are Multiple Constraints on Organisms – the total diversity of form, function and environmental resilience exhibited by organisms are awe-inspiring, each individual operates within a relatively narrow range of constraints. Constraints fundamentally take 2 forms (1) physical and (2) evolutionary.

9. Chance is important - chance events play a critical role in ecology. The opening of a gap in a forest canopy will have major impact on the ecology of local fauna and flora

10. The Boundaries of Ecology are in the mind of the Ecologists – mathematics, chemistry, physics, statistics and other natural sciences are tools essential to the understanding of ecology

Adaptation to the Environments

• Fitness – The fitness of an individual will be high if that individual gives rise to many offspring which themselves are reproductively successful , fitness will not necessarily be maximized by producing the most offspring – it may be better to produce fewer, larger offspring which will have better survivorship.

•Natural Selection - survival of the fittest

• Adaptation – Any heritable trait possessed by an organism which aids survival or reproduction is an adaptation. Such traits may be physiological, morphological or behavioral.

•Genotype and Phenotype – The genotype is the genetic composition of an individual, the phenotype is the organism and how it looks like

The Niche• Niche – the position an organism fills in its environment, comprising the conditions under which it is found, the resources it utilizes and the time it occurs..

• Habitat – the physical environment where an organism is found

• Multidimensional Niche Space – each condition or resource which defines the niche of an organism contributes one dimension to the space in which the organism can occur. Considering all dimensions together defines fully the organisms niche.

• Fundamental Niche – the niche space an organism can fill in the absence of competition or predation is known

• Realized Niche – the niche space occupied by an organism when competition and predation occur , this is the realized niche which is always a subset of the fundamental niche

Solar Radiation – solar energy drives climatic processes. Energy from the sun strikes the earth where high energy wavelengths of light are absorbed and re-emitted in the form of radiant heat.

Rain – rain falls when moist air cools. Warm air can hold more water than cool air, so cooling causes water droplets t o condense and fall as rain.

Global Wind Patterns – The major systems of the earth from the upward movements of warm air around the equator, which is replaced by cooler air coming from the north and south forming the trade winds. The Coriolus effect (cause by the earths rotation) deflects moving air to the right of the northern hemisphere and to the left of the southern hemisphere. The trade winds meet just to the of the equator in the inter tropical convergence zone (ITCZ)

Circulation of Oceans – The worlds oceans are stirred by winds. Trade winds pile up water against continents, causing an imbalance in sea levels.

Solar Radiation

Cloud and Rain on Windward Slope

Rising air cools before condensation

Above the condensation level cooling takes place

Air is no longer saturated once descent commences and therefore warms

20o

10o

4o

24o

Condensation Level

Sea Level

Precipitation along Mountain Ranges

Microclimate – this is the climate in which plants and animals live, and is scaled to the organism in that the microclimate of a tree is different in scale to the microclimate of beetle larvae in the soil. Microclimate differs from climate which prevails above the first few meters over the ground, primarily in the intensity of the c of the changes with elevation and the change with time

Soil Water – for terrestrial plants the main source of water is the soil which serves as a reservoir. Water enters the reservoir as rain or melting snow and passes through the soil pores. The upper limit of the water holding capacity is called the field capacity. This is the amount of water which can be held by soil pores against the force of gravity. Plants cannot extract all the water held in the soil pores as they cannot exert sufficient suction force to extract water from the narrow soil pores. The lower limit of water availability is thus determined by the physiology of the plant species and is known as the permanent wilting point, this is the soil water content at which plats wilt and are unable to recover.

Micro-climate

Water Drains Freely Water unavailable to plantsAvailable Water

Rootlet Diameters

Field Capacity

Permanent wilting Point

Pore Size (microns)

1000 100 10 1 0.1 0.01 0.001

The status of water in the soil as measured by the diameter of soil pores that remain water –filled.

Homeotherms and Poikilotherms - As environmental temperature rises, Homeotherms maintain an approximately constant body temperature, while the body temperature of Poikilotherms varies with environmental temperature

Ectotherms and endotherms – ectotherms are organisms such as plants, reptiles which are largely reliant on external sources of heat to raise their body temperature. Endotherms are organism capable of generating heat internally in order to raise their body temperature.

Heat Exchange – all organisms gain heat from and lose heat to their environment as well a producing heat. A variety of physiological and behavioral mechanisms are used to regulate heat.

Temperature thresholds – There are 3 main temperature ranges of interest; very low, very high and the temperature between. The most dangerous thing about high temperature is that they lie only a few degrees above the animal’s metabolic optimum a result of the physico-chemical properties of their enzymes. The frequent effect of high temperature is dehydration.

Temperature

Radiation from atmosphere

Conduction exchange

Radiation exchange

Evaporative exchange

Reflected sunlight

Re-radiation

Reflected

radiation

Direct radiation

Avenues of Heat Exchange between Ectotherm and physical environment

Nutrients•Nutrient Sources – Nutrients are gained and lost by communities in a variety of ways. Mechanical weathering, chemical weathering, particularly carbonation are important processes.Simple dissolution of minerals in water also makes nutrients available from rock and soil. Water may carry nutrients in watercourses providing an important source too, in downstream areas. Atmospheric gases provide nutrient sources too, particularly CO2 and nitrogen. Other nutrient from the atmosphere become available to communities as Wet fall (rain, fog) or Dry fall (setting of particles during dry periods).

•Nutrient budgets in Terrestrial Communities – a particular nutrient atom taken by an organism may cycle continuously until eventually the nutrient will be lost through any one of a number of processes that remove nutrients from the system. Release may be direct to the atmosphere or via bacterial action. For many elements the most substantial pathway of loss is in Streamflow. Other pathways of nutrient loss include fire, the harvesting of crops and deforestation.

•Geochemistry – the pools of chemical elements on earth exit in various compartments: in rocks (the lithosphere) and soil water, streams,lakes or oceans. In all these cases the chemical elements exist in inorganic form.

Global Biogeochemical Cycles – Nutrients can be moved over vast areas by the atmosphere or by water current. There are no boundaries to this movement. Terrestrial plants utilize atmospheric CO2 as their carbon source for photosynthesis, whereas aquatic plants use dissolved carbonates. Respiration releases the carbon locked in photosynthetic products back to the atmospheric and hydrospheric carbon compartments. The atmospheric phase is predominant in the global nitrogen cycle in which nitrogen fixation and denitrification by microorganisms is of particular importance.

Atmosphere

Ocean SedimentsRock

Water in Rivers, lakes, soil + oceans

Aquatic Communities

Terrestrial Communities Human Activities

Biotic uptake Run-off

Streamflow

Biotic Uptake

Major Global Pathway of Nutrients between hydrosphere, Lithosphere and biotic reservoir

Sedimentation

Increased Emission

Weathering

Precipitation

Gaseous and Aerosol Uptake Land Clearance,

Forestry, Agriculture

Plants and ConsumersThe Fate of Matter in the Community – The main elemental component of living matter is carbon. C enters the trophic structure of a community when CO2 is fixed through photosynthesis, the utilization of the energy of sunlight to combine CO2 and water into sugars.

Producers – Autotrophs, the main producers in most terrestrial ecosystems, use energy from the sun or from the oxidation of inorganic substances to produce organic molecules from inorganic ones. Plants are the main producers in terrestrial systems.

Consumers – plants are eaten by primary consumers such as grazing mammals and insects. These primary producers are in turn eaten by secondary consumers, carnivores such as mammals and spiders.

Decomposers – the organic material that composes living organisms in an ecosystem is eventually recycled, broken down and returned to the abiotic environment in forms that can be used by pants. The most important decomposers are bacteria and fungi

InteractionsCompetition – Interaction among individuals utilizing a limited resource,

resulting in reduced fitness in the competing individuals.

Predation – Consumption of all or part of another individual (the prey). This wide definition encompasses

(1) True predators, which kill their prey soon after attacking them

(2) Grazers, which consume only part of prey

(3) Parasites,which live in vary close association with a single prey(the host) often inside the host;s tissues.

Mutualism – a positive reciprocal relationship between two individuals of different species which results in increased fitness of both parties. Mutualism may be symbiotic, in which the organisms live together in close physical association

Components and ProcessesThe Concept of Ecosystem – This concept was proposed by Tansley in 1935 and was originally defined to include all the animals, plants and physical interactions of a defined space. Modern ecologists think of the ecosystem in terms of energy flow or nutrient cycles.

Ecosystem components – The bodies of living organisms within a unit area constitute a standing crop of biomass; the mass of organisms per unit area of ground (or water) usually expressed in units of energy or dry organic matter (e.g. tons per hectare).

Ecosystem and Laws of Thermodynamics – the first law of thermodynamics states that “energy can neither be created nor destroyed. The second law of thermodynamics states that every transformation results in a reduction of the free energy of the system.

Transfer Efficiencies – the proportion of net primary production that flows through trophic levels depends on transfer efficiencies in the way energy is used and passed from one step to the next.

A general model of trophic structure and energy flow for a terrestrial community

Respiration

Carnivore II

Carnivore I

Detrivore

Net Primary Production

Bodies

and

Feces

Carnivore II

Carnivore I

Herbivore

Respiration

Dead Organic Matter

Primary and Secondary Production

Primary production Global net primary productivity is approximately 120x109 tons dry weight per year on land and 50 x 109 tons per year in the sea. The most productive systems are found amongst marshland, estuaries, reefs and cultivated land. Productivity decreases moving away from the equator indicating the importance of temperature and radiation.

Secondary production – is defined as the rate of production of new biomass by heterotrophic organisms,.

The Pattern of Energy Flow through a trophic compartment

Productivity at Trophic Level N

Energy intake at trophic level n

Respiratory heat loss at trophic

level n

Productivity available for consumption from trophic level

Dead Organic Matter Compartment

Not consumed

Fecal energy loss at trophic level n

Diagram to show relationship between energy flow and nutrient cycling

Grazing System

Net Primary Production

Decomposer System

Dean Organic matter

Respiratory Heat Loss

Radiant Energy

Respiratory Heat Loss

Food Chains

Pathways of Nutrient Flow – autotrophic organisms assimilate inorganic resources into packages of organic molecules. These become the resources of heterotrophs which then become a resource for another consumer. At each link in this food chain we can recognize three (3) pathways to the next trophic level: decomposition, parasitism and predation.

Interaction between Trophic Levels – a characteristic of an ecosystem is the number and nature of the species that occupy its various trophic levels. The relationship and constituents of adjacent trophic levels may be described by a food chain. This is a chain of eating and being eaten.

Top-down or bottom-up – It has been argued that the earth is green and vegetated because herbivore numbers are regulated by their predators (top-down) while all other trophic levels are regulated by competition for resources (bottom-up control)

A Diagrammatic representation of a Food Web from Wytham Wood near Oxford UK, from Ecology 2nd ed. King 1989

herbs

Herbivorous insects

Spiders

Mice

Owl

Blue & great tits (bird)

Trees and Bushes

Weasels

Winter moth

Cyzenis (parasite)

Totrix

Oak Trees

Other Leaf feeders

Ground Beetles

Litter

Soil Insect and mites

Earthworm

Fungi

Shrew Moles

Grazing Food Web

Rice Forage grasses Atis

Bug

MouseGrasshopper Aphids

Praying mantisChicken

Cow

Hawk

Man

Bird

Ant

Cat Snake

Community, Structure and Stability

Community – an an assemblage of species populations that occur together in the same place at the same time. It has properties determined by the interactions among individuals such as competition and parasitism. The community can also be viewed in terms of species diversity, food-webs, energy flow and the interactions among guilds of species.

Community Structure – Species diversity of a community depends on the number of different species it contains (the species richness) and the evenness of species abundance across species.

Guilds – these are groups of species that occupy similar niches such as insects feeding on broad-leaved trees form one guild.

Community Stability – There are 2 components of stability, these are resilience and resistance, which describe the communities ability to recover from disturbance and to resist change.

Community Patterns, Competition and Predation

Community Assembly - The concept of assembly rules attempts to explain how natural communities vary from random assemblage derived from the range of available species. Community assembly may be influenced by habitat type, species colonization, parasitism and establishment or interspecific relationships such as parasitism and competition

Competition – can be an important force shaping community structure but is not necessarily significant at the time of investigation. The ghost of competition past can leave a strong imprint on a community (e.g. niche differentiation)

Grazers – grazing animals have 2 effects on plat communities (a)their selective feeding affects species abundance in the community and (b) grazing suppresses the growth of competitive species thus enhancing and maintaining the diversity of less competitive species.

Carnivores – Selective predation and prey switching can leave rarer species unpredated. This behavior can lead to the co-existence of a large number of relatively rare species in the same communities

Keystone species - this term is applied to any species whose removal would have a significant effect on community structure

Succession

The Classical Concept – Ecological succession is defined as a continuous unidirectional sequential change in the species composition of a natural community. The sequence of community is termed a “sere” and culminates in the climax.

Autogenic Succession – this is self driven, resulting from the interaction between organisms and their environment. Primary succession occurs on a newly formed substrate such as glacial till. Secondary succession follows disturbance

Degradative Succession – this is a type of autogenic succession involving colonization and subsequent decomposition of dead organic matter. Different species invade and disappear in turn, as the degradation of the organic mater uses up some resources and makes others available. This process leads to the production of humus and is important in soil formation.

Allogenic Succession – this results from external environmental factors such as long term climatic change (e.g. ice ages) or environmental change over a short time (e.g. sediment accretion). Changes in community structure over time are apparent from pollen analysis of sediment cores.

Successional Process : succession is influenced by 3 processes

•Facilitation - changes in the environment that are imposed by the developing community and allow other species to invade

•Inhibition – species of one stage resist invasion by later successional species such that invasion is only possible following disturbance or death

•Tolerance – late successional species invade because they are able to tolerate lower resource levels and can out compete early successional species.

Ecosystem Patterns

Vegetation and Climate – The earth’s vegetation is divided into distinct blocks or formations which broadly reflect climatic conditions. This pattern arises as a result of the adaptation of plat form to temperature and water availability.

Ecotones – On the local and regional scale communities vary as the individual species respond to environmental gradients. The physical and biological structure of a community will change in response o conditions such as moisture, altitude and soil type. This type of variation is known as zonation. Biomes are large areas of approximately uniform habitat that merge into each other along ecotones

Biomes

Grasslands – these biomes occur when rainfall is intermediate between that of deserts and forests. There are 2 major types of grasslands depending on temperature : tropical grasslands (savannah) and temperate grasslands (steppe -Europe, prairie – north America and pampas-south America)

• Tropical grasslands receive up to 1200 mm (60 in) of rain in the wet season but none during the prolonged dry season

•Temperate grasslands are moderately dry, having 250-600 mm (10-30 in) of rainfall per annum, but amount of available water will depend on the temperature, seasonal distribution of rainfall and water holding capacity of soil

Tundra – The arctic tundra forms a circumpolar band between the arctic ocean and the polar ice caps to the north and the coniferous forest of the south. Smaller but ecologically similar regions found above the tree line on high mountain re alpine tundra. These ecosystems have low productivity.

Forests – These ecosystems tend to have high net productivity and also a high biomass. The clearing of tropical rainforest result in biodiversity loss, depletes the soil and may lead to erosion.

Desert – these ecosystems are found around latitudes 30oN and 30oS, they have less that 50mm of annual rainfall, hot days and cold nights, soils are nutrient poor, thin and freely drained

Saltwater Biomes – these are open oceans, continental shelves, the inter-tidal zone and coral reefs, salt march, mudflats and mangroves. Physical factors namely tides, currents, temperature, pressure(depth) and light intensity determine the make-up of biological salt water communities

Freshwater Biomes – these include lakes, rivers, bogs, marshes and swamps. These systems are fed by water and nutrients leaching from surrounding catchments.

ConservationRare Species – the type of rarity depends on 3 attributes of the species in question

•Size of geographical range

•Habitat specificity

•Local population size

Any species for which one or more of these attributes is low demonstrates some form of rarity.

Genetic Diversity – A species which has declined to low numbers will suffer from a loss of genetic diversity and inbreeding depression

Habitat Loss and fragmentation – numerous habitats, such as wetlands, grasslands and forests have been either drastically reduced in area, modified or destroyed,usually for agriculture.

Extinction – this is a natural process. Although its pace and incidence have been increased through human activity.

Conservation StrategiesBiodiversity - a term encompassing the variety of organisms at all levels from genetic variants belonging to the same species to species diversity and including the variety of ecosystems.

The Earth Summit , Rio de Janeiro –The importance of biodiversity has been promoted by the International Convention on Biological Diversity, part of the earth summit in 1992. In addition Agenda 21 is a blue print to encourage sustainable development socially, economically and environmentally

Strategies for Conservation – Conservation strategies exist in a range of different levels of details and scale, global, national, regional and local to accommodate the markedly different political scales at which conservation objectives are directed.

• World Conservation Union

• The Convention on International Trade in Endangered Species

The Design of Nature Reserves – In general the larger the reserve, the greater the number of species in it,. However, many small areas may contain more species in total than one reserve of the same area. The debate over the relative merits of a single large or several small reserves is known as the “SLOSS” argument. The best compromise may be a network of small linked reserves which allow dispersal and genetic interchange to take place between areas.

Environmental Assessment – is the means by which the conservation value of a site may be assessed without detailed and time consuming surveys of its entire biodiversity.

TheEnd