Ecological Niches and Energy Systems

Ecological Niches

  • Definition: An ecological niche describes the functional position and role of an organism within its environment.

    • It includes all abiotic and biotic interactions that contribute to an organism's survival.

Components of an Ecological Niche:

  • Abiotic: The habitat and associated resources such as sunlight, temperature, and oxygen levels.

  • Biotic: An organism's activity patterns and interactions, including its mode of nutrition and competition.

  • Example Bird Niche components: Habitat, Resources, Food Source, Predators, Activity

Competition and Niche Uniqueness

  • Niches are unique; no two species can share the exact same niche.

  • Sharing the exact niche would lead to direct competition for space and resources, resulting in a struggle for survival.

  • Competition can lead to two possible outcomes:

    • Competitive Exclusion: One species uses resources more efficiently, driving the other to local extinction.

    • Resource Partitioning: Species alter their habitat usage to divide available resources.

Fundamental vs. Realized Niches

  • Competition may restrict a species from occupying its entire potential niche.

  • Fundamental Niche:

    • The entire set of conditions under which an organism can survive and reproduce (where it could live).

    • It represents the theoretical habitat (e.g., the entirety of a tree).

  • Realized Niche:

    • The set of conditions utilized by an organism after interactions with other species (where it does live).

    • It represents the actual habitat (e.g., specific branches of a tree).

Modes of Nutrition

  • An organism's niche is also defined by how it obtains food for metabolism (nutrition).

  • Two primary modes of nutrition exist:

    • Autotrophic (Self-Feeding): Manufacturing organic molecules from CO2CO_2 and an energy source.

    • Heterotrophic (Feeding on Others): Obtaining organic compounds from other organisms via digestion.

Types of Nutrition

  • Photosynthesis:

    • Utilizes energy from light absorption to synthesize food.

    • Performed by plants, algae, and some prokaryotes (Autotrophs).

  • Chemosynthesis:

    • Utilizes energy from chemical reactions to synthesize food.

  • Saprotrophic:

    • Secreting enzymes to break down organic material externally (Decomposers).

  • Holozoic:

    • Consuming food and breaking down organic material internally (Consumers).

    • Food is ingested, digested internally, then absorbed and assimilated.

Autotrophic Nutrition

  • Autotrophs synthesize organic compounds (food) from inorganic substances (e.g., CO2 , H2O)

  • Most autotrophs use photosynthesis, where light serves as the initial energy source.

  • Examples include plants, most algae, and certain bacteria like cyanobacteria and green algae.

Holozoic Nutrition

  • Heterotrophs obtain organic nutrients by feeding on other organisms.

  • Involves ingestion, internal digestion, absorption, and assimilation.

  • Includes consumers (feed on living organisms), scavengers (feed on carrion), and detritivores (feed on detritus).

Saprotrophic Nutrition

  • Saprotrophs are heterotrophs that live on or inside non-living organic matter.

  • They secrete digestive enzymes to break down the material externally before absorption.

  • Referred to as decomposers, including bacteria, fungi, and molds.

Mixotrophic Nutrition

  • Mixotrophs use both autotrophic and heterotrophic nutrition.

    • Obligate Mixotrophs: Must use both forms of nutrition.

    • Facultative Mixotrophs: Can survive using either form.

  • Examples:

    • Euglena (freshwater protist) possesses chlorophyll (autotrophic) and feeds on detritus (heterotrophic).

    • Dinoflagellates (mixotrophic marine plankton).

    • Coral make organic compounds via their symbiotic algae

    • Insectivorous plants (e.g., Venus flytraps) feed on small insects for nutrients in waterlogged soil (low nitrogen).

Nutritional Adaptations

  • Organisms possess specific adaptations based on nutritional requirements.

    • Plants: Adapted for harvesting light and resisting herbivores.

    • Herbivores: Adapted for feeding on plant matter and resisting predation.

    • Carnivores: Adapted for finding, catching, and killing prey.

    • Omnivores: Adapted for consuming both plant and animal matter.

Ecosystems as Open Systems

  • Energy systems are classified as open or closed based on exchanges with surroundings.

    • Open Systems: Exchange both energy and matter with their surroundings.

    • Closed Systems: Exchange energy but not matter with their surroundings.

  • Ecosystems are open systems involving interactions between organisms and their environment.

Energy Sources

  • Ecosystems require a continuous energy influx to sustain life and metabolic activity.

  • Sunlight is the primary energy source for most ecosystems; light converts into chemical energy via photosynthesis, then released by cellular respiration.

  • Communities without sunlight (e.g., deep sea, underground caves) derive energy from oxidizing inorganic molecules via Chemosynthesis.

Photosynthesis

  • Photoautotrophs convert light energy to chemical energy through photosynthesis.

  • Chemical energy is stored in carbon compounds (organic molecules).

  • These organic compounds serve as building blocks for macromolecules.

  • All green plants, certain algae, and some prokaryotes are photosynthetic.

  • CO2 + H2O — Light + Chlorophyll —> Glucose + O2
    *Note: Some phototrophs convert light to chemical energy without synthesizing carbon compounds. These organisms do not undertake photosynthesis and gain organic compounds via feeding

Chemosynthesis

  • Chemoautotrophs derive energy from oxidation reactions involving inorganic compounds.

  • These compounds include ammonia, hydrogen gas, hydrogen sulfide, or iron oxide.

  • Organisms are found where light cannot penetrate (deep sea or underground).

  • Iron-oxidizing soil bacteria are a common example.

  • CO2 + H2S + O2 + \rightarrow Glucose + S + H2O

Cell Respiration

  • Living organisms release energy from organic compounds via cell respiration.

  • Energy is produced by oxidation reactions (high energy electrons are released & transferred to ATP).

  • ATP hydrolysis (to ADP + Pi) releases energy to power cell activity.

  • Glucose + O2 \rightarrow CO2 + H_2O + ATP</p></li></ul><h3id="41c8784b−4f2f−45b0−b142−9dc6f2f863c4"data−toc−id="41c8784b−4f2f−45b0−b142−9dc6f2f863c4"collapsed="false"seolevelmigrated="true">TrophicLevels</h3><ul><li><p>Heterotrophsacquireorganiccompoundsviafeedingonotherorganisms.</p></li><li><p>Anorganism′srelativepositioninafeedingsequenceisitstrophiclevel.</p><ul><li><p>Level1:Producers(e.g.,plankton)</p></li><li><p>Level2:PrimaryConsumers(e.g.,shrimp)</p></li><li><p>Level3:SecondaryConsumers(e.g.,crab)</p></li><li><p>Level4:TertiaryConsumers(e.g.,shark)</p></li></ul></li><li><p>ProducerscanbePHOTO(usingsunlight)orCHEMO(usingchemicalreactions).</p></li></ul><h3id="3aee5eb4−aa1f−4052−b0fc−65777951e60e"data−toc−id="3aee5eb4−aa1f−4052−b0fc−65777951e60e"collapsed="false"seolevelmigrated="true">Producers</h3><ul><li><p>Autotrophssynthesizeorganiccompounds(glucose)fromsimpleinorganicsubstances(e.g.,</p></li></ul><h3 id="41c8784b-4f2f-45b0-b142-9dc6f2f863c4" data-toc-id="41c8784b-4f2f-45b0-b142-9dc6f2f863c4" collapsed="false" seolevelmigrated="true">Trophic Levels</h3><ul><li><p>Heterotrophs acquire organic compounds via feeding on other organisms.</p></li><li><p>An organism's relative position in a feeding sequence is its trophic level.</p><ul><li><p>Level 1: Producers (e.g., plankton)</p></li><li><p>Level 2: Primary Consumers (e.g., shrimp)</p></li><li><p>Level 3: Secondary Consumers (e.g., crab)</p></li><li><p>Level 4: Tertiary Consumers (e.g., shark)</p></li></ul></li><li><p>Producers can be PHOTO(using sunlight) or CHEMO(using chemical reactions).</p></li></ul><h3 id="3aee5eb4-aa1f-4052-b0fc-65777951e60e" data-toc-id="3aee5eb4-aa1f-4052-b0fc-65777951e60e" collapsed="false" seolevelmigrated="true">Producers</h3><ul><li><p>Autotrophs synthesize organic compounds (glucose) from simple inorganic substances (e.g.,CO2andandH2O).</p></li><li><p>Energycomesexternallyfromsunlight(phototrophs)oroxidationreactions(chemotrophs).</p></li><li><p>Autotrophsarecalledproducersastheymaketheirownorganiccompounds.</p></li><li><p>Producersoccupythefirstlevelofafeedingpathwayandincludeplants,algae,andsomebacteria.</p></li></ul><h3id="2bd446de−4e17−46e6−8300−cbab3df4ec99"data−toc−id="2bd446de−4e17−46e6−8300−cbab3df4ec99"collapsed="false"seolevelmigrated="true">Consumers</h3><ul><li><p>Heterotrophsusecarboncompoundsfromotherorganismstosynthesizeorganicmolecules.</p></li><li><p>Heterotrophsthatuseinternaldigestionareconsumers.</p></li><li><p>Consumersoccupyallbutthefirstleveloffeedingpathways.</p></li><li><p>Consumersarecategorizedbyfoodsource:</p><ul><li><p>Herbivores:Feedonvegetation.</p></li><li><p>Carnivores:Feedonanimalmatter.</p></li><li><p>Omnivores:Feedonplantandanimalmatter.</p></li></ul></li></ul><h3id="fda37e1c−a185−4f13−881c−4ab941ff84ee"data−toc−id="fda37e1c−a185−4f13−881c−4ab941ff84ee"collapsed="false"seolevelmigrated="true">Decomposers</h3><ul><li><p>Saprotrophsareheterotrophicorganismsobtainingorganicnutrientsfromdeadorganismsviaexternaldigestion.</p></li><li><p>Theyliveon/insidenon−livingorganicmaterial,secretedigestiveenzymes,andabsorbproducts.</p></li><li><p>Theybreakdowncarboncompoundsofdeceasedmaterialand,therefore,arecalleddecomposers.</p></li><li><p>Includebacteria,fungi,andmoldsbutarenottypicallyshowninthefeedingpathway.</p></li></ul><h3id="b0773cd5−3b21−4af7−a11f−e96921e50949"data−toc−id="b0773cd5−3b21−4af7−a11f−e96921e50949"collapsed="false"seolevelmigrated="true">FoodChains</h3><ul><li><p>Foodchainsdemonstratelinearfeedingrelationshipsbetweenorganisms.</p></li><li><p>Arrowsrepresentenergyandmattertransferasorganismsareeaten.</p></li><li><p>Example:Producer→1ºConsumer→2ºConsumer→3ºConsumer→4ºConsumer</p></li></ul><h3id="41092ae0−9244−49cd−bf42−f9def8eadb24"data−toc−id="41092ae0−9244−49cd−bf42−f9def8eadb24"collapsed="false"seolevelmigrated="true">FoodWebs</h3><ul><li><p>Foodwebsdemonstrateinterrelatedfeedingpathwayswithmultiplefoodsources.</p></li><li><p>Organismsmayoccupymorethanonetrophiclevel.</p></li></ul><h3id="66048601−2542−4134−bded−8ce2ef6778bd"data−toc−id="66048601−2542−4134−bded−8ce2ef6778bd"collapsed="false"seolevelmigrated="true">FeedingRestrictions</h3><ul><li><p>Energyislostbetweentrophiclevels,reducingenergyobtainedfromfeeding.</p></li><li><p>Highertrophiclevelsmusteatlargerquantitiesofpreyandexpendmoreenergyhuntingwhichmakesitunviabletokeepaddinglevels.</p></li><li><p>Theconstantenergylosslimitsthenumberoftrophiclevels.</p></li><li><p>Energycontentpermassisconstant,soasenergyislostthetotalmassofatrophiclevel(biomass)willalsobereduced.Thisleadstofewerorsmallerorganismsathigherlevels.</p></li></ul><h3id="fe83e8ad−4167−4ae5−9a0f−b86b56189652"data−toc−id="fe83e8ad−4167−4ae5−9a0f−b86b56189652"collapsed="false"seolevelmigrated="true">EnergyLoss</h3><ul><li><p>Energyavailabilityreducesateachfoodchainstageduetoenergylossesbetweentrophiclevels.</p></li><li><p>Storedchemicalenergylostvia:</p><ul><li><p>Cellrespiration(metabolism).</p></li><li><p>Remainingunconsumed(bones).</p></li><li><p>Undigested(feces).</p></li><li><p>Convertedintothermalenergy(heat).<br>∗Note:Saprotrophswilldecomposeundigestedmaterial</p></li></ul></li></ul><h3id="f9cd4408−675b−4e6e−8955−33418283e489"data−toc−id="f9cd4408−675b−4e6e−8955−33418283e489"collapsed="false"seolevelmigrated="true">EnergyEfficiency</h3><ul><li><p>Organismsreleasethermalenergy(heat)whenproducingATPviacellrespiration.</p></li><li><p>Livingorganismscannotconvertheatenergyintootherusableforms.</p></li><li><p>Energyisalwayslostfromanecosystemandmustbeconstantlyreplaced.</p></li><li><p>Energytransformationsinlivingorganismsarebetween5−20).</p></li><li><p>Energy comes externally from sunlight (phototrophs) or oxidation reactions (chemotrophs).</p></li><li><p>Autotrophs are called producers as they make their own organic compounds.</p></li><li><p>Producers occupy the first level of a feeding pathway and include plants, algae, and some bacteria.</p></li></ul><h3 id="2bd446de-4e17-46e6-8300-cbab3df4ec99" data-toc-id="2bd446de-4e17-46e6-8300-cbab3df4ec99" collapsed="false" seolevelmigrated="true">Consumers</h3><ul><li><p>Heterotrophs use carbon compounds from other organisms to synthesize organic molecules.</p></li><li><p>Heterotrophs that use internal digestion are consumers.</p></li><li><p>Consumers occupy all but the first level of feeding pathways.</p></li><li><p>Consumers are categorized by food source:</p><ul><li><p>Herbivores: Feed on vegetation.</p></li><li><p>Carnivores: Feed on animal matter.</p></li><li><p>Omnivores: Feed on plant and animal matter.</p></li></ul></li></ul><h3 id="fda37e1c-a185-4f13-881c-4ab941ff84ee" data-toc-id="fda37e1c-a185-4f13-881c-4ab941ff84ee" collapsed="false" seolevelmigrated="true">Decomposers</h3><ul><li><p>Saprotrophs are heterotrophic organisms obtaining organic nutrients from dead organisms via external digestion.</p></li><li><p>They live on/inside non-living organic material, secrete digestive enzymes, and absorb products.</p></li><li><p>They break down carbon compounds of deceased material and, therefore, are called decomposers.</p></li><li><p>Include bacteria, fungi, and molds but are not typically shown in the feeding pathway.</p></li></ul><h3 id="b0773cd5-3b21-4af7-a11f-e96921e50949" data-toc-id="b0773cd5-3b21-4af7-a11f-e96921e50949" collapsed="false" seolevelmigrated="true">Food Chains</h3><ul><li><p>Food chains demonstrate linear feeding relationships between organisms.</p></li><li><p>Arrows represent energy and matter transfer as organisms are eaten.</p></li><li><p>Example: Producer → 1º Consumer → 2º Consumer → 3º Consumer → 4º Consumer</p></li></ul><h3 id="41092ae0-9244-49cd-bf42-f9def8eadb24" data-toc-id="41092ae0-9244-49cd-bf42-f9def8eadb24" collapsed="false" seolevelmigrated="true">Food Webs</h3><ul><li><p>Food webs demonstrate interrelated feeding pathways with multiple food sources.</p></li><li><p>Organisms may occupy more than one trophic level.</p></li></ul><h3 id="66048601-2542-4134-bded-8ce2ef6778bd" data-toc-id="66048601-2542-4134-bded-8ce2ef6778bd" collapsed="false" seolevelmigrated="true">Feeding Restrictions</h3><ul><li><p>Energy is lost between trophic levels, reducing energy obtained from feeding.</p></li><li><p>Higher trophic levels must eat larger quantities of prey and expend more energy hunting which makes it unviable to keep adding levels.</p></li><li><p>The constant energy loss limits the number of trophic levels.</p></li><li><p>Energy content per mass is constant, so as energy is lost the total mass of a trophic level (biomass) will also be reduced. This leads to fewer or smaller organisms at higher levels.</p></li></ul><h3 id="fe83e8ad-4167-4ae5-9a0f-b86b56189652" data-toc-id="fe83e8ad-4167-4ae5-9a0f-b86b56189652" collapsed="false" seolevelmigrated="true">Energy Loss</h3><ul><li><p>Energy availability reduces at each food chain stage due to energy losses between trophic levels.</p></li><li><p>Stored chemical energy lost via:</p><ul><li><p>Cell respiration (metabolism).</p></li><li><p>Remaining unconsumed (bones).</p></li><li><p>Undigested (feces).</p></li><li><p>Converted into thermal energy (heat).<br>*Note: Saprotrophs will decompose undigested material</p></li></ul></li></ul><h3 id="f9cd4408-675b-4e6e-8955-33418283e489" data-toc-id="f9cd4408-675b-4e6e-8955-33418283e489" collapsed="false" seolevelmigrated="true">Energy Efficiency</h3><ul><li><p>Organisms release thermal energy (heat) when producing ATP via cell respiration.</p></li><li><p>Living organisms cannot convert heat energy into other usable forms.</p></li><li><p>Energy is always lost from an ecosystem and must be constantly replaced.</p></li><li><p>Energy transformations in living organisms are between 5-20% efficient (roughly 10%).</p></li></ul><h3 id="df10f64a-eeed-4063-b4af-a6fea6eaed5d" data-toc-id="df10f64a-eeed-4063-b4af-a6fea6eaed5d" collapsed="false" seolevelmigrated="true">Energy Pyramids</h3><ul><li><p>Energy pyramids show energy amounts at each feeding position.</p></li><li><p>Unit = energy per area per time (J.m^{-2}.year^{-1}$$).

  • Energy pyramid never appears inverted.

    • Producers are at the base.

    • Consumers occupy successive levels.

    • Only ~10% of chemical energy is transferred.

    • Each level is roughly one-tenth the previous level.