ch ecology
Phylogeny and Evolutionary Reconstruction
Overview: Biology is fundamentally the study of evolutionary patterns and processes. Phylogeny, the study of evolutionary relationships among groups of organisms, provides the essential tools to reconstruct the history of life. These reconstructions help us understand why organisms exhibit their diverse characteristics, how they are related to one another through common ancestry, and ultimately, they inform our understanding of fundamental evolutionary processes such as adaptation, speciation, and diversification.
Practical aim: The primary goal for biologists is to build a phylogenetic tree (or cladogram) to visually represent these evolutionary relationships. This tree serves as a powerful hypothesis about the historical connections among species, guiding new questions about their evolution, trait development, and ecological interactions.
Taxonomy, Taxa, and Linnean Ranks
Taxon (plural: taxa): A formal designation for a group of organisms at any specific level within the Linnean hierarchical classification system. Examples include a species (e.g., Homo sapiens), a genus (e.g., Felis), a family (e.g., Felidae), an order, a class, or a phylum. Taxa are meant to represent monophyletic groups.
Linnean ranks (examples, from most inclusive to least inclusive): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species. It's important to note that Domain is not an original Linnean rank; Linnaeus established his system before the discovery of microbial diversity and the recognition of the three major domain-level groups in life (Bacteria, Archaea, Eukarya). Domains were added much later to reflect fundamental prokaryotic-eukaryotic distinctions and the two prokaryotic lineages.
Taxon vs. taxa: "Taxon" refers to a singular group (e.g., the Class Mammalia is a taxon), while "taxa" is its plural form, referring to multiple groups (e.g., mammals, birds, and reptiles are distinct taxa).
Ingroup, Outgroup, and Polarizing Characters
Ingroup: This is the designated study group, comprising the set of taxa whose relationships are of primary interest for phylogenetic inference. These are the organisms for which we aim to reconstruct the evolutionary history.
Outgroup: An outgroup is a strategically chosen taxon or a set of taxa that is known to be outside the ingroup but is closely related to it. The outgroup serves two critical functions:
Rooting the tree: It provides a point of reference to determine the ancestral state of characters, thereby establishing the direction of evolution within the ingroup.
Inferring character state polarity: By comparing character states in the ingroup to the outgroup, we can determine which traits are ancestral and which are derived.
How to choose an outgroup: The selection of an outgroup relies on information external to the dataset being used for the current phylogenetic reconstruction (e.g., previous phylogenetic studies, fossil evidence, or morphological analyses). It must be sufficiently divergent from the ingroup to represent the ancestral condition but not so divergent that it offers no useful comparison.
Rationale: Traits observed in the outgroup are generally regarded as the ancestral state (plesiomorphic) for the ingroup. Conversely, traits that differ in the ingroup compared to the outgroup are considered derived (apomorphic). These derived traits are particularly crucial because they diagnose and define monophyletic groups within the ingroup.
Ancestral trait (plesiomorphy): A character state that is shared with the outgroup and is presumed to have been present in the common ancestor of the ingroup and outgroup. By itself, a plesiomorphy is not informative for defining specific relationships within the ingroup because it represents a shared ancient characteristic.
Derived trait (apomorphy): A character state that evolved within the ingroup (or its immediate ancestor) and is not present in the outgroup. Apomorphic traits are fundamental for identifying and defining monophyletic groups because they represent recent, shared evolutionary novelties.
Key Concepts: Monophyly, Ancestral vs Derived, and Synapomorphy
Monophyly: A monophyletic group, also known as a clade, is the most desirable and natural grouping in phylogenetics. It consists of a Most Recent Common Ancestor (MRCA) and all of its descendants. This means every organism descended from that MRCA is part of the monophyletic group, and no descendants are excluded. Monophyletic groups accurately reflect true evolutionary history.
MRCA: The Most Recent Common Ancestor is the most recent individual or population from which all organisms in a given set of taxa are descended. Identifying the MRCA is central to defining clades.
Synapomorphy (shared derived trait): A derived trait (apomorphy) that is shared by two or more taxa and inherited from their immediate common ancestor. Synapomorphies are the defining characteristics of a monophyletic group, as they provide evidence of shared evolutionary history not present in more distant relatives.
Plesiomorphy (ancestral trait): An ancestral character state used to describe a lineage. While informative about character evolution, plesiomorphies are not diagnostic for a monophyletic group because they are widely shared with ancestors and outgroups.
Sister taxa: Two taxa (or groups of taxa) that are each other’s closest relatives. They share an immediate common ancestor not shared by any other group. For example, if A and B share an MRCA, and C and D share a different MRCA, then A and B are sister taxa to each other, and C and D are sister taxa to each other.
Non-monophyletic groups: These groups fail the complete descendant criterion and do not accurately reflect evolutionary history. They come in two main types:
Paraphyletic group: Contains an MRCA but excludes some of its descendants. An example is the traditional group "Reptilia," which excludes birds, despite birds descending from the MRCA of reptiles.
Polyphyletic group: Consists of taxa that do not share an immediate common ancestor but instead are grouped based on convergent traits (traits that evolved independently). For instance, grouping bats and birds based on flight would be polyphyletic, as their MRCA did not fly.
Jargon and Conceptual Clarity: An Example Using a Backbone Trait
Backbone as a trait example: Consider the presence or absence of a backbone. Vertebrates possess a backbone (a derived state), while invertebrates do not (the ancestral state within the animal kingdom). However, the term "invertebrate" itself is problematic if used to imply a single, cohesive evolutionary group. Grouping all life without backbones (e.g., plants, fungi, bacteria, and all non-vertebrate animals) into "invertebrates" is highly misleading. These groups are not closely related to each other; they simply retain the ancestral characteristic of lacking a backbone, which is a plesiomorphy.
The derived state (presence of a backbone) clearly identifies vertebrates as a distinct, monophyletic grouping (a clade). The ancestral state (absence of a backbone) defines a much broader, more ancestral, and importantly, paraphyletic group (animals without backbones, excluding vertebrates). This highlights why relying solely on ancestral traits to define groups can lead to misleading biological classifications.
We use numerous traits, both morphological and molecular, to build a consistent and robust story about evolutionary relationships. This approach allows us to avoid illogical groupings, such as grouping snails (mollusks) with vertebrates based purely on the shared ancestral condition of not having a backbone. Instead, we seek derived traits (synapomorphies) that unite genuine clades.
Derived vs Ancestral Traits: Apomorphies and Plesiomorphies
Derived traits are formally called apomorphies. When an apomorphy is shared by multiple taxa due to common ancestry, it is a synapomorphy, and these are the critical indicators that diagnose monophyletic groups.
Ancestral traits are formally called plesiomorphies. When a plesiomorphy is shared by multiple taxa from a common ancestor, it is a symplesiomorphy. Symplesiomorphies do not define monophyletic groups because they are too broadly distributed across lineages.
Example in the narrative: If we consider a series of trait sets, a derived trait like "presence of feathers" diagnoses the monophyletic group "birds." However, "presence of a notochord" is an ancestral trait for all chordates and would not by itself diagnose a specific monophyletic group within chordates (like chordates + vertebrates, excluding other chordates).
Outgroup Method in Practice: Worked Example with Real Taxa
Taxa involved (ingroup and outgroup):
Ingroup: Crocodilians (including Alligatoridae and Crocodylidae), Birds (Aves), Mammals, Jawless Chordates (Agnatha).
Other comparative groups: Platyhelminthes (flatworms), Nematoda (roundworms – often grouped under "Nemathelminthes" in older classifications, representing non-jawed invertebrate groups).
Outgroup: Cnidaria (e.g., jellyfish, sea anemones, corals). Cnidarians are highly divergent, exhibiting radial symmetry and lacking the complex organ systems of bilaterians, making them a suitable distant outgroup to polarize characters for the ingroup.
Goal: To reconstruct the phylogenetic relationships of these diverse taxa using a small, illustrative set of morphological traits.
Trait 4: Crop/gizzard presence or absence:
Observation: Crocodilians and Birds (Aves) possess a muscular stomach (crop/gizzard) used for grinding food, often aided by swallowed stones. This is a specialized digestive adaptation.
Absence: Mammals, jawless chordates, flatworms, and cnidarians largely lack this specific crop/gizzard structure.
Significance: The presence of a crop/gizzard is a synapomorphy that supports the monophyly of Crocodilians + Aves. This derived trait is also observed in some extinct groups, such as certain dinosaurs, reinforcing the evolutionary link between birds and crocodilians through their shared reptilian ancestry.
Trait 2: Presence of a jaw:
Observation: Taxa with jaws include Crocodilians, Birds, and Mammals.
Absence: Jawless groups include Agnatha (e.g., lampreys, hagfish) and the more distant outgroups like Platyhelminthes and Cnidaria.
Significance: The presence of a jaw is a synapomorphy that defines a monophyletic group called Gnathostomata (jawed vertebrates), which includes all jawed fish, amphibians, reptiles, birds, and mammals.
Resulting monophyletic pairings (based on these and other traits, illustrating the build-up of the tree):
Crocodilians + Aves form a strong monophyletic group, supported by synapomorphies like the crop/gizzard and other shared anatomical features (e.g., specific skull architecture, four-chambered heart).
Mammals are identified as a sister group to the clade containing Crocodilians + Aves, all within a larger monophyletic grouping (Amniota, defined by the amniotic egg).
Trait: Notochord presence/absence:
Significance: The notochord is a flexible, rod-like structure that is a defining feature during the embryonic development of all chordates (which includes vertebrates, cephalochordates, and urochordates). Importantly, in most vertebrates, the notochord is largely replaced by the vertebral column (backbone) during development; it does not become the backbone itself, but rather induces its formation.
Trait: Bilateral body symmetry:
Observation: Most vertebrates (e.g., mammals, birds, fish) and many invertebrates (e.g., flatworms, roundworms, insects) exhibit bilateral symmetry, meaning their body can be divided into two mirror-image halves along a central plane.
Contrast: Cnidarians (e.g., jellyfish) typically exhibit radial symmetry, where body parts are arranged around a central axis.
Discussion points:
Sea urchins: While adult sea urchins display superficial pentaradial symmetry, their larval stages are bilaterally symmetric. This illustrates that they are fundamentally deuterostomes within Bilateria, and radial symmetry in adults is a secondary acquisition in their lineage, not a primary ancestral state for the entire group.
The example emphasizes how multiple traits (morphological, anatomical, developmental) are used in combination to infer robust phylogenetic relationships. It also strongly demonstrates why determining polarity (ancestral vs. derived) is crucial for constructing logically sound and evolutionarily accurate groups.
Takeaway: This case study vividly illustrates the practical application of the outgroup method, how to diagnose monophyletic groups with unambiguous synapomorphies, and how to identify when a proposed group is not monophyletic due to the exclusion of descendants (paraphyly) or the reliance on convergent traits (polyphyly).
Jargon Recap: Why Monophyly Matters in Phylogeny
Monophyly is the organizing principle for modern taxonomy and phylogenetics because it directly reflects and represents true evolutionary history. Unlike paraphyletic or polyphyletic groups, monophyletic groups do not require extra, ad hoc (made up for a specific situation) explanations to justify their grouping, as their shared ancestry is explicit.
Monophyletic groups are robustly supported by shared derived traits (synapomorphies) and are unequivocally defined by their common ancestry with a Most Recent Common Ancestor (MRCA).
Non-monophyletic groups inherently misrepresent evolutionary relationships. Their recognition typically necessitates additional explanations (e.g., explaining why a descendant was excluded, or why a trait evolved convergently) or ultimately, reclassification to align with the true evolutionary narrative.
Ecology: Linking Ecology to Evolution and Phylogeny
What determines where organisms live? The distribution of species is a complex interplay of environmental factors and their evolutionary history. The lecture contrasts the primary factors influencing distribution in terrestrial vs. aquatic contexts.
Terrestrial organisms: Climate, specifically temperature and precipitation, are the primary abiotic determinants of species distribution at large scales. These two factors dictate the dominant vegetation types, which in turn define habitats and food sources for animal communities.
Climographs: These are graphical representations that plot the average annual temperature against average annual precipitation for different terrestrial biomes. Each biome (e.g., temperate broadleaf forest, northern coniferous forest, deserts, grasslands, tropical rainforests, tundra) occupies distinct zones on a climograph, with some overlap, reflecting the specific climatic conditions required to support their characteristic plant and animal communities. For example, deserts are characterized by low precipitation and variable temperatures, while tropical rainforests have high temperatures and high precipitation.
Aquatic environments: In aquatic systems (lakes, oceans), light availability (photic zone) and nutrient concentrations are the dominant drivers of organism distribution and productivity.
Light attenuation with depth: Light rapidly diminishes as it penetrates water. The photic zone is the upper layer where enough light is available for photosynthesis. Below this is the aphotic zone, where light is insufficient for primary production. This depth gradient profoundly affects photosynthetic organisms (like phytoplankton) and, consequently, the entire food web.
Nutrient accumulation: Nutrients like nitrates and phosphates, essential for life, tend to accumulate at the bottom of aquatic systems, in what's known as the benthic zone, due to decomposition and gravitational settling of organic matter.
The turnover phenomenon in freshwater systems (deep ponds/lakes):
In temperate regions, deep lakes undergo seasonal mixing events called turnover (typically in spring and fall). During summer, a thermocline forms - a distinct layer where water temperature drops rapidly with depth, creating a barrier between warmer, less dense surface water and colder, denser bottom water. This stratification prevents mixing.
In spring and fall, as surface temperatures change and approach the temperature of deeper water (4^ ext{o} ext{C} for maximum density), the water column becomes less stratified. Wind action then becomes effective in mixing the entire water column. This process rotates nutrient-rich bottom water upward (benefitting surface phytoplankton) and oxygen-rich surface water downward, thereby replenishing oxygen in deeper waters (reducing hypoxic or anoxic conditions) and distributing nutrients throughout the lake. This seasonal renewal is critical for ecosystem health.
Photic vs. Aphotic zones: The photic zone is the sunlit surface layer where photosynthetic organisms (primary producers) thrive. The aphotic zone is the deep, dark layer where light is insufficient for photosynthesis, and life relies on organic matter drifting down from above or chemosynthesis.
Zonation and nutrients: The benthic zone (bottom sediments) is rich in nutrients due to the accumulation and decomposition of organic matter (detritus). This fertilization of the benthos supports a diversity of benthic organisms, including decomposers and specialized feeders.
Biotic vs. Abiotic factors controlling distribution:
Biotic factors: Living components that influence distribution. These include:
Dispersal limitations: The physical ability of an organism to move and establish in a new area (e.g., geographical barriers).
Predators: Presence or absence of predators can limit prey populations.
Parasites and disease: Can significantly impact population health and distribution.
Competition: For resources (food, space, mates) with other species.
Symbiotic relationships: Mutualism, commensalism, and parasitism can also affect where organisms can thrive.
Abiotic factors: Non-living physical and chemical components of the environment. These include:
Temperature: Directly affects metabolic rates and enzyme activity.
Oxygen (O_2) availability: Crucial for aerobic respiration; highly variable in aquatic systems.
Carbon dioxide (CO2) availability: Essential for photosynthesis. CO2 dissolves poorly in water compared to air, which can limit photosynthetic rates in aquatic environments, especially for phytoplankton.
pH and salinity: Chemical properties of the soil or water that affect physiological processes.
Nutrient availability: Levels of nitrogen, phosphorus, and other essential elements.
Autotrophs and energy flow:
Autotrophs: "Self-feeders" — organisms capable of producing their own organic compounds from inorganic sources. They form the base of most food webs. They obtain energy from either light or chemical reactions.
Photoautotrophs: Use light energy (sunlight) to convert inorganic carbon (CO_2) into organic matter (e.g., sugars) through photosynthesis. Most primary producers on Earth are photoautotrophs (plants, algae, cyanobacteria).
Chemoautotrophs: Derive energy from the oxidation of inorganic chemical compounds (e.g., hydrogen sulfide, ammonia) to synthesize organic molecules. These are found in unique environments like deep-sea hydrothermal vents, within soils, and in some anoxic sediments.
Most primary producers are photoautotrophs, capturing solar energy to fuel the vast majority of ecosystems.
Primary producers and consumers:
Primary producers (autotrophs): Form the first trophic level. They are consumed by primary consumers (herbivores), which feed directly on plants or algae.
Secondary consumers (carnivores): Feed on primary consumers.
Tertiary/Quaternary consumers: Feed on secondary or tertiary consumers, respectively.
Energy flow is unidirectional: Energy enters ecosystems primarily from the sun (or chemical reactions for chemoautotrophs) and flows through trophic levels. It is irreversibly lost as heat at each transfer, never recycled in the same way matter is.
Energy flow and inefficiency in ecosystems:
A fundamental principle of ecology (and thermodynamics): Most energy is lost as heat at each transfer between trophic levels due to metabolic activities, incomplete consumption, and waste. This loss means energy transfer is highly inefficient.
The 10% rule: A common ecological approximation states that only about 10% of the energy from one trophic level is transferred to the next higher trophic level. The remaining ~90% is typically lost as metabolic heat or remains unconsumed/undigested.
The sun as the ultimate energy source: While the sun provides immense energy, plants (primary producers) capture only a small fraction of the incident solar energy, typically around 1% (or even less) through photosynthesis. This small captured energy forms the entire energy budget that feeds the rest of the ecosystem through the food web.
The caterpillar energy budget (illustrative example):
Let's consider a hypothetical caterpillar that consumes plant material containing approximately 200 ext{ J} of energy.
Approximately 30 ext{ J} (or about 15% of the ingested energy) might be assimilated and converted into its own growth (biomass increase) or reproduction.
A significant portion, approximately 70 ext{ J}, is consumed by the caterpillar's metabolic processes (respiration, movement, maintaining body temperature).
Of the assimilated energy, roughly half, or 35 ext{ J}, is wasted as heat or lost through excretion, emphasizing further inefficiencies.
Calculation Breakdown: If 200 ext{ J} is ingested:
Assimilated Energy (used for growth/metabolism): Assume 100 ext{ J} is assimilated (the rest is egested as waste).
Growth/Reproduction: 30 ext{ J} (part of assimilated energy, leads to biomass increase).
Respiration (Metabolism, lost as heat): 70 ext{ J} (part of assimilated energy, fuels life processes but is lost from the food chain).
Egested Waste (not assimilated): 100 ext{ J} (initial ingested - assimilated energy, lost immediately as feces).
This detailed accounting illustrates that a substantial portion of the initial input energy is lost to waste and heat at each step. This high inefficiency is a major constraint on ecosystem structure, limiting the number of trophic levels typically observed in most ecosystems.
Key terms to know and understand their roles:
Autotrophs: Organisms that produce their own food.
Photoautotrophs: Use light as an energy source for food production.
Chemoautotrophs: Use chemical reactions as an energy source for food production.
Primary producers: Autotrophs forming the base of the food web.
Primary consumers (herbivores): Organisms that feed on primary producers.
Secondary/tertiary/quaternary consumers (carnivores/omnivores): Organisms that feed on primary, secondary, or tertiary consumers, respectively.
Phytoplankton: Microscopic, photosynthetic organisms that float in aquatic environments; major primary producers in oceans and lakes.
Zooplankton: Microscopic animal plankton that feed on phytoplankton and other zooplankton.
Detritus: Non-living organic matter composed of dead organisms and waste products.
Decomposers: Organisms (e.g., bacteria, fungi) that break down detritus, recycling matter and essential nutrients back into the ecosystem for producers to reuse.
Reiteration of energy vs. matter:
Matter (chemical nutrients), such as carbon, nitrogen, and phosphorus, is recycled continually through ecosystems via biogeochemical cycles, with detritus and decomposers playing a crucial role in making these nutrients available again.
Energy flows unidirectionally through ecosystems, entering (primarily from the sun) and being used up or dissipated as heat. It is not recycled in the same way as matter; new energy inputs are constantly required to sustain life.
Takeaways: How Ecology Connects to Evolution and Phylogeny
Ecology and evolutionary theory are inextricably linked: Ecological pressures, such as resource availability, competition, predation, and climate, act as powerful agents of natural selection. These selective pressures drive evolutionary changes in populations over generations, leading to adaptation, speciation, and the diversification of life forms.
The distribution of organisms is fundamentally shaped by both their intrinsic dispersal ability (their capacity to reach and colonize new environments) and the complex interplay of biotic and abiotic factors present in a given environment. Organisms evolve to thrive in specific environmental niches.
Understanding energy flow and nutrient cycling within ecosystems is crucial for explaining why the trophic structure (the organization of food webs) evolves in particular ways. It also elucidates why certain lineages succeed and proliferate in specific habitats, reflecting their evolutionary adaptations to exploit available energy and resources efficiently.
Here are the definitions for the key terms based on the provided lecture notes:
Linnean Hierarchy: A hierarchical classification system (Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species) used to formally designate groups of organisms, with Domain being a later addition.
Binomial Nomenclature: This specific term is not explicitly defined in the provided notes.
Phylogeny: The study of evolutionary relationships among groups of organisms, providing tools to reconstruct the history of life.
Monophyly: A group (also known as a clade) consisting of a Most Recent Common Ancestor (MRCA) and all of its descendants, accurately reflecting true evolutionary history.
Non-monophyly: Groups that do not accurately reflect evolutionary history, failing the complete descendant criterion (e.g., paraphyletic and polyphyletic groups).
Derived Trait / Apomorphy: A character state that evolved within the ingroup (or its immediate ancestor) and is not present in the outgroup; fundamental for defining monophyletic groups.
Ancestral Trait / Plesiomorphy: A character state shared with the outgroup and presumed to have been present in the common ancestor of the ingroup and outgroup; not informative for defining specific relationships within the ingroup.
Taxa/Taxon: A formal designation for a group of organisms at any specific level within the Linnean hierarchical classification system (Taxon = singular, Taxa = plural).
Sister Taxa: Two taxa (or groups of taxa) that are each other's closest relatives, sharing an immediate common ancestor not shared by any other group.
Ingroup: The designated study group comprising the set of taxa whose relationships are of primary interest for phylogenetic inference.
Outgroup: A strategically chosen taxon or set of taxa known to be outside the ingroup but closely related, used to root the tree and infer character state polarity.
Terrestrial Organisms: Organisms whose distribution at large scales is primarily determined by climate, specifically temperature and precipitation.
Climate: A primary abiotic determinant of species distribution for terrestrial organisms, involving temperature and precipitation.
Temperature: A key abiotic factor influencing both terrestrial (along with precipitation, defining biomes) and aquatic organism distribution, directly affecting metabolic rates and enzyme activity.
Precipitation: A key abiotic factor, along with temperature, determining the distribution of terrestrial organisms and characteristic plant/animal communities.
Aquatic Organisms: Organisms whose distribution and productivity in systems like lakes and oceans are dominantly driven by light availability and nutrient concentrations.
Light: For aquatic organisms, its availability in the photic zone is crucial for photosynthesis, rapidly diminishing with depth.
Nutrients: Concentrations of essential elements (like nitrates, phosphates) that are dominant drivers of organism distribution and productivity in aquatic systems.
Photic Zone: The upper layer of aquatic systems where enough light is available for photosynthesis.
Aphotic Zone: The deep, dark layer of aquatic systems where light is insufficient for primary production.
Benthic Zone: The bottom sediments of aquatic systems, rich in nutrients from accumulated and decomposed organic matter.
Biotic Factors: Living components that influence organism distribution, including dispersal limitations, predators, parasites, disease, competition, and symbiotic relationships.
Mutualism: A type of symbiotic relationship (a biotic factor) that can affect where organisms thrive.
Commensalism: A type of symbiotic relationship (a biotic factor) that can affect where organisms thrive.
Parasitism: A type of symbiotic relationship (a biotic factor) that can affect where organisms thrive.
Abiotic Factors: Non-living physical and chemical components of the environment, such as temperature, oxygen availability, carbon dioxide availability, pH, salinity, and nutrient availability.
Water & Oxygen: Essential abiotic factors, with oxygen (O_2) being crucial for aerobic respiration and highly variable in aquatic systems, while water availability is critical for all life.
Salinity: A chemical property of soil or water that affects physiological processes as an abiotic factor.
Sunlight: The ultimate energy source, captured by photoautotrophs, fueling the vast majority of ecosystems.
Soil: An abiotic component whose properties (like pH and salinity) affect physiological processes.
Energy & Food: The basis of ecosystem function; energy enters, flows unidirectionally through trophic levels, and is largely lost as heat, while food provides chemical energy and matter.
Primary Producer: Autotrophs (e.g., plants, algae, cyanobacteria) that form the first trophic level, producing their own organic compounds from inorganic sources (mainly via photosynthesis or chemosynthesis).
Consumer: Organisms that obtain energy by feeding on other organisms. This includes primary consumers (herbivores), secondary consumers (carnivores feeding on primary consumers), and tertiary/quaternary consumers.
Secondary Production: The amount of chemical energy in consumers' food that is converted to their own new biomass during a given period (e.g., for a caterpillar, converting ingested energy into growth).
Production Efficiency = 4 to 40%: The efficiency with which an organism converts assimilated energy into new biomass. For example, a caterpillar might assimilate ~15% of ingested energy for growth and reproduction.
Trophic Level: A position in a food chain or ecological pyramid, representing how far an organism is from the primary producers (e.g., primary producers, primary consumers, secondary consumers).
Trophic Efficiency = 10%: The common ecological approximation stating that only about 10% of the energy from one trophic level is transferred to the next higher trophic level, with the remaining ~90% lost mostly as heat or unconsumed material.