B4.2 Ecological Niches PDF

## B4.2 Ecological Niches ### What are the advantages of specialized modes of nutrition for living organisms? When Charles Darwin was sent a Christmas orchid (Angraecum sesquipedale) from Madagascar, which has a nectar tube 300 millimeters long, he predicted that an insect with such long mouthparts...

## B4.2 Ecological Niches ### What are the advantages of specialized modes of nutrition for living organisms? When Charles Darwin was sent a Christmas orchid (Angraecum sesquipedale) from Madagascar, which has a nectar tube 300 millimeters long, he predicted that an insect with such long mouthparts must exist in the same ecosystem to act as a pollinator for the orchid. This moth was finally discovered 21 years after Darwin’s death, and it was aptly named *Xanthopan praedicta*. Its mouthparts are 300 millimeters long and curl up when not in use. They uncurl like a party blower when the moth is preparing to insert them into the nectar tube. What do you think Darwin based his prediction on? ### How do adaptations of a species relate to its niche in an ecosystem? Kettlehole ponds dominate the landscape created by glacial retreat. At different depths, the pond can be seen to have zones with different plants. The deeper the water, the less light penetrates and the lower the oxygen concentration in the bottom mud. The main challenge in shallow water is drought during the summer, particularly near the edges of the pond. This is why the species inhabiting the edges have advantageous structural adaptations. What types of plants would thrive in the center of the pond? What would thrive at the edges? **NM & NS** * B4.2.1 Ecological Niche as a Function of a Species in an Ecosystem * B4.2.2 Differences between organisms that are obligate anaerobes, facultative anaerobes, and obligate aerobes * B4.2.3 Photosynthesis as a mode of nutrition for plants, algae, and some groups of photosynthetic prokaryotes * B4.2.4 Holozoic nutrition in animals * B4.2.5 Mixotrophic nutrition in certain protists * B4.2.6 Saprophytic nutrition in certain fungi and bacteria * B4.2.7 Diversity of nutrition in archaea * B4.2.8 Relationship between dentition and diet of representative omnivorous and herbivorous members of the hominid family * B4.2.9 Adaptations of herbivores to feed on plants, and of plants to resist herbivory * B4.2.10 Adaptations of predators to find, capture, and kill their prey, and of animals that are prey to resist predation * B4.2.11 Plant adaptations in the shape of plants for light capture * B4.2.12 Fundamental and realized niches * B4.2.13 Competitive exclusion and the uniqueness of ecological niches ## B4.2.1 Ecological Niche as a Function of a Species in an Ecosystem One of the fundamental hypotheses of ecology is that each species plays a unique role in the ecosystem it inhabits; this is known as the ecological niche. Ecological niches have biotic and abiotic components. * **Abiotic factors:** The tolerance zones of abiotic variables determine the habitat of a species, where it lives in the ecosystem. * **Biotic factors:** Food is obtained through synthesis using sunlight, water, and carbon dioxide, or from other organisms. To minimize competition, species must specialize. To effectively compete, they must develop adaptations for their particular mode of nutrition. Other species are used to provide a wide range of services, such as the recycling of minerals, the pollination of flowers, or the dispersal of seeds: support from trees in terms of their trunks and branches. An ecological niche is composed of many factors: it is multidimensional. A species will only survive, grow, or reproduce if all the conditions of its niche are met in the ecosystem. ## Figure 3: Two Aspects of the Periwinkle’s Niche Two aspects of the periwinkle's niche are the size of its prey and the height at which it forages. The graph shows the percentage of the diet according to these two variables in an oak woodland in California. There are many other aspects to the ecological niche of this bird. ## B4.2.2 Differences between Organisms that Are Obligate Anaerobes, Facultative Anaerobes, and Obligate Aerobes Animals and plants require oxygen for aerobic cellular respiration, but some organisms do not. Some microorganisms can only survive in the complete absence of molecular oxygen (O2), including some species of bacteria, archaea, and protists. Anoxic (lack of oxygen) conditions occur in swamps, waterlogged soils or muds, the digestive tracts of animals, and the deep parts of lakes and seas. Living organisms are often grouped into one of three categories based on their oxygen requirements. | Category | Requirements | Examples | | ---------------- | ------------------------ | ------------------------------------------------------------------ | | Obligate Aerobes | Require a continuous supply of oxygen, so they can only live in oxygen-rich environments. | All animals and plants; *Micrococcus luteus* (skin bacteria) | | Obligate Anaerobes | Oxygen inhibits or kills them, so they only live in oxygen-free environments. | *Clostridium tetani* (tetanus bacteria), methanogenic archaea | | Facultative Anaerobes | Can use oxygen if it is present, but can live with or without oxygen. | *Escherichia coli* (intestinal bacteria), *Saccharomyces* (yeast)| ## Activity: Winogradsky Columns To prepare a Winogradsky column, mud and water from a pond are placed in a large bottle or graduated cylinder with other miscellaneous materials. The column is sealed and exposed to light. Oxygen and other substance concentration gradients develop in the column, with colored bands due to groups of bacteria and archaea growing where concentrations are suitable. ## B4.2.3 Photosynthesis As A Mode Of Nutrition For Plants, Algae, and Some Groups of Photosynthetic Prokaryotes In photosynthesis, light energy is used to fix carbon dioxide and build sugars, amino acids, and other carbon compounds required for life. There are three groups of photosynthesizers: * Plants: including mosses, ferns, conifers, and flowering plants. * Eukaryotic algae: including marine algae that grow on rocky shores and single-celled algae such as *Chlorella*. * Various groups of bacteria, including cyanobacteria (blue-green bacteria) and purple bacteria. Therefore, photosynthesis occurs in two of the three domains of life: eukaryotes and bacteria, but not archaea. ## Figure 5: Winogradsky Column in a Glass Bottle ## B4.2.4 Holozoic Nutrition in Animals Animals obtain their supplies of carbohydrates, amino acids, and other carbon compounds by eating food. They are heterotrophs because their carbon compounds come from other organisms. Molecules such as polysaccharides and proteins are digested before they are absorbed. Digestion in most animals occurs internally, after food has been taken in. This is called holozoic nutrition. Holozoic nutrition involves the following stages: 1. **Ingestion**: Food intake. 2. **Digestion**: Breaking down food. 3. **Absorption** - Transporting digested food across the plasma membrane of epithelial cells into the blood and the tissues. 4. **Assimilation**: Using digested food to synthesize proteins and other macromolecules. 5. **Egestion**: Excretion of undigested waste. Some animals digest their food externally, and therefore are not holozoic. For example, spiders inject digestive enzymes into their prey and suck up the liquid produced. They absorb digestion products in their gut and then assimilate them. ## Figure 6: Holozoic Nutrition Diagram ## B4.2.5 Mixotrophic Nutrition In Certain Protists Autotrophs produce their own carbon compounds from simple substances, including carbon dioxide. Heterotrophs obtain their carbon compounds from other organisms. Some single-celled eukaryotes (protists) use both methods. Organisms that are not exclusively autotrophs or heterotrophs are called mixotrophs. Facultative mixotrophs can be completely autotrophic, heterotrophic, or use both methods. *Euglena gracilis*, for example, has chloroplasts and carries out photosynthesis when sufficient light is present but can feed on detritus or smaller organisms by endocytosis, meaning it is a facultative mixotroph. Obligate mixotrophs can not grow without both autotrophic and heterotrophic modes of nutrition. These organisms cannot synthesize a particular carbon compound that they require from their food source. In some cases, a protist that does not have its own chloroplasts will obtain them by consuming algae. It uses these ‘kleptochloroplasts’ to carry out photosynthesis until they degrade and need to be replaced. ## B4.2.6 Saprophytic Nutrition in Certain Fungi and Bacteria Saprophytes secrete digestive enzymes onto organic matter, digest it externally, and then absorb the products of digestion. Many types of bacteria and fungi are saprophytes. They are also called decomposers because they break down carbon compounds in dead organic matter and release elements such as nitrogen back into the ecosystem, which allows these elements to be used again by other organisms. ## Activity: Determining Trophic Level By answering a series of simple questions about the mode of nutrition of an organism, it’s usually possible to determine which trophic level it fits into. The questions are presented in Figure 13 in the form of a dichotomous key, which is a series of paired choices. The key works for both single-celled and multicellular organisms, but not parasites, such as tapeworms, or fungi that cause diseases in plants. ## Figure 12: Saprophytic Fungi Saprophytic fungi grow on the surface of fallen leaves and break them down by releasing digestive enzymes. ## Figure 13: Dichotomous Key ## Questions Based On Data: Fishing In Marine Food Webs Marine trophic levels (TL) can be represented by a number that indicates the position of a species within an ecosystem. By definition, producers sit at TL = 1. Primary consumers have TL = 2 and so forth. The higher the number, the more energy transfer stages separate the organism from the initial capture of solar energy. TLs are not always whole numbers. Fish and other animals that forage at more than one level are assigned an average TL. One effect of overfishing is a reduction in the number of fish that forage at higher TLs (i.e., long-lived fish). The phrase "fishing down marine food webs" refers to the increasing trend of catch consisting of animals foraging at lower TLs (Figure 14). 1. Suggest a method that could be used to determine the TL of a fish once it has been caught. 2. a. Compare changes in the average TL of fish caught in marine and freshwater fisheries since 1970. b. Suggest why there is a difference in the two trends. 3. Explain why an individual fish's average TL may increase with age. 4. Infer change in the age of the captured fish over the study period. 5. Explain two advantages of catching and consuming fish at a lower average TL. ## Figure 14: Evolution of Mean Trophic Level for Fish Captured over 30 Years ## B4.2.7 Diversity of Nutrition in Archaea There are three domains of life: archaea, bacteria, and eukaryotes. Archaea are single-celled and lack a nucleus, like bacteria. However, archaea are more similar to eukaryotes in other ways. Some types of archaea are adapted to extreme environments such as hot springs, salty lakes, and caustic lakes. They are harder to cultivate in the laboratory, meaning that they have been studied less than the other domains of life. Archaea are highly diverse in their energy sources. There are three main categories: * **Phototrophs:** Absorption of light energy by pigments other than chlorophyll * **Chemotrophs:** Oxidation of inorganic chemical products, such as Fe2+ to Fe3+ * **Heterotrophs:** Oxidation of carbon compounds obtained from other organisms. ## B4.2.8 Relationship Between Dentition and Diet of Representative Omnivorous and Herbivorous Members of the Hominid Family The Hominidae family includes the genera containing humans (*Homo*), orangutans (*Pongo*), gorillas (*Gorilla*), and chimpanzees (*Pan*). Some members of the Hominidae family have exclusively herbivorous diets and others are omnivorous; their diets include prey animals. Living members of the Hominidae family exhibit a relationship between diet type and dentition. This can be studied using physical collections of skulls in natural history museums or digital collections online, such as eSkeletons.org, a database created by The University of Texas at Austin. The teeth of herbivores tend to be large and flat for grinding fibrous plant tissues. Omnivores tend to have a mix of different tooth types for breaking down both meat and plants in their diets. Humans have flat molars at the back of their mouth for crushing and grinding food, and their canines and incisors are sharper than those of herbivores for tearing tougher food items, such as meat. Once the structure-function relationships have been established, the diet of extinct species in the Hominidae family, such as *Homo floresiensis* and *Paranthropus robustus*, can be inferred from their dentition. ## Figure 15: Chimpanzee Dentition Chimpanzees have very large canines compared to humans. ## Activity: Diet Deduction Figure 16 shows the fossilized jaw and teeth of an *Australopithecus anamensis* individual, who lived about 4.1 million years ago. The jaw in Figure 17 belongs to a female *Homo neanderthalensis* who lived over 110,000 years ago (before the last glacial period). What can be deduced about their diets? ## Figure 16: *Australopithecus anamensis* Jaw ## Figure 17: *Homo neanderthalensis* Jaw ## Theories: Making Inferences About Diet From Fragmentary Evidence In science, a theory is a general explanation that can be applied broadly. Theories are based on observed patterns. Predictions can be made from these theories through deductive reasoning. Observations of dentition in animals with known diets, including herbivores, carnivores, and omnivores, can be used to develop theories about structure-function relationships of teeth. These theories can be tested by predicting the diet of living animals based on the characteristics of their teeth and then checking if the actual diet matches the prediction. This can confirm the theory or demonstrate that it is false and needs to be rejected. Inferences about the diet of extinct hominid species can be made using theories about dentition. However, we cannot confirm these predictions because we cannot be certain what the diet of an extinct hominid would have been. So are such predictions unscientific? What if skeletons of prey species are found near the remains of an extinct hominid? Could that increase certainty? ## B4.2.9 Adaptations of Herbivores to Feed on Plants and of Plants to Resist Herbivory Animals that feed exclusively on plants are herbivores and have structural features that adapt them to their diet. The mouthparts of insects are very diverse, but they are all homologous: they are derived through evolution from the same ancestral mouthparts. Most insects are herbivores. Insects that feed on leaves can be broadly divided into two groups: * **Chewing insects**: Beetles and other insects that have mandibles for biting, chewing, and ingesting pieces of leaves. * **Piercing-sucking insects**: Aphids and other insects that have tubular mouthparts for piercing leaves or stems to access the phloem tubes and feed on the sap. ## Figure 18: *Sagra buqueti*: An Example of a Chewing Insect A rainbow beetle uses its mandibles to chew leaves. ## Figure 19: *Macrosiphum rosae*: An Example of a Piercing-Sucking Insect A rose aphid uses its piercing mouthparts to access sap. ## Figure 20: Thorns on *Saribus rotundifolius* Thorns on a palm tree serve as a defense mechanism against herbivores. ## Figure 21: Stinging Hairs on *Urtica ferox* Nettle plants have stinging hairs as a defense mechanism. ## Figure 22: Milkweed Plant Milkweed plants produce cardiac glycosides, which are toxic to herbivores. *Aphis nerii* (oleander aphids) tolerate the cardiac glycosides and can accumulate them. This makes the aphids themselves toxic to predators. Plants exhibit a variety of adaptations for deterring attacks by herbivores. Some have hard, sharp spines, which means the herbivore risks getting injured when trying to eat them. Others have a stinging substance that causes pain. Many plants synthesize substances that are toxic to herbivores. These are known as secondary metabolites. (Primary metabolites are substances that are part of basic metabolic pathways of a cell.) They can be stored anywhere in a plant, but they are often found concentrated in seeds, which are attractive to herbivores because of their high protein, starch, or fat content. In some cases, herbivores have evolved metabolic adaptations to break down toxins in plants, showing a plant-herbivore specificity, where only a few species of herbivores are adapted to feed on a single plant. ## B4.2.10 Adaptations of Predators to Find, Capture, and Kill Their Prey and of Animals that are Prey to Resist Predation Predators are adapted for finding suitable prey, capturing it, and killing it. Prey can be killed before it is eaten or it can die inside the predator's digestive system. Prey species have adaptations to resist predation. Table 2 shows some selected examples of adaptations, but there are many more. These adaptations can be structural, chemical, or behavioral. ## Figure 23: *Desmodus rotundus*: An Example of a Predator with Specialized Dentition The common vampire bat has unique dentition: small premolars and no molars, but large canines and incisors in its upper jaw that are sharp and pointed for piercing prey, enabling it to feed on blood. ## Figure 24: *Phalera bucephala*: An Example of a Cryptically Colored Prey A buff-tip moth resembles broken birch twigs, providing camouflage when it rests during the day on twigs or on the ground. This is when night-flying moths are most vulnerable to predation. ## Figure 25: *Dendroaspis polylepis*: A Predator with a Highly Toxic Venom The black mamba produces venom containing a mixture of neurotoxins, including a cholinesterase inhibitor. The venom paralyzes prey when it is injected via its fangs. The snake can swallow its prey without resistance. ## Figure 26: *Tyria jacobaeae*: A Prey Species with Aposematic Coloration The cinnabar moth caterpillar stores toxic alkaloids from its food source, ragwort. The insect's black and yellow stripes warn predators of its toxicity. The red and black coloration of the adults indicates that they continue to store toxins even after they emerge from their pupal stage. ## Figure 27: *Ursus arctos*: A Predator That Uses Learned Strategies Brown bears have learned different strategies for ambushing salmon. Some bears wait at the top of a waterfall for a fish to jump out of the water, and others stick their heads under the water and watch for fish swimming by. ## Figure 28: *Lutjanus kasmira*: A Prey Species with Antipredator Behavior Blue-striped snapper fish swim in shoals with frequent erratic changes in direction. This behavior reduces the possibility of predation because it is easier for a shoal to spot threats and harder for a predator to isolate an individual. ## Figure 29: *Cyanistes caeruleus*: An Example of a Bird Using a Learned Behavior Blue tits have learned to feed on cream from milk bottles after ripping open the aluminum lids. ## B4.2.11 Plant Adaptations in the Shape of Plants for Light Capture In habitats where there is enough water for abundant plant growth and temperatures are suitable for photosynthesis, plants compete for light. Forest ecosystems develop in such areas. Plants use different strategies in forests to access sunlight. Their shapes show high diversity. * **Canopy trees**: These trees develop a dominant shoot that grows rapidly to reach the forest canopy, where they are shaded less by other trees. * **Lianas**: These plants climb other trees for support, so they do not need to produce as much xylem (wood) as freestanding trees. * **Epiphytes**: Epiphytes grow on the trunks and branches of trees, getting more light than they would if they were on the forest floor, but there is little soil for their roots. * **Strangler epiphytes**: These plants grow up the trunks of trees, eventually enveloping the tree and blocking its foliage, eventually killing the tree. * **Understory shrubs and herbs**: These plant communities grow in the shade of the forest, absorbing light that reaches the forest floor. ## Figure 30: Diversity of Plant Shapes in a Tropical Rainforest Tropical rainforests have a diversity of plant shapes, including trees, vines, and epiphytes. ## B4.2.12 Fundamental and Realized Niches Living organisms tolerate a wide range of biotic and abiotic conditions, but their adaptations do not allow them to survive outside of this range. This range of tolerance is known as the fundamental niche of the species. In the absence of competition, the species would occupy its entire fundamental niche. In natural ecosystems, competition occurs. As a result, a species is usually excluded from parts of its fundamental niche by competitors. The actual extent of the potential range that a species occupies is called the realized niche. ## Figure 31: Fundamental vs. Realized Niche A realized niche is a subset of a fundamental niche. This reduction in the realized niche is due to overlap with other species’ niches. ## B4.2.13 Competitive Exclusion and the Uniqueness of Ecological Niches When the fundamental niches of two species overlap, it is expected that one species will exclude the other from that area of distribution through competition. This was experimentally demonstrated using the flour beetles *Tribolium castaneum* and *Tribolium confusum*. When reared together in different combinations of temperature and humidity, *T. castaneum* excluded *T. confusum* in some conditions, but *T. confusum* was more successful under other conditions. In the pie charts of Table 3, blue segments show the percentage of trials where *T. confusum* excluded *T. castaneum*, and the orange segments indicate the opposite. ## Table 3: Competition Between *T. castaneum* and *T. confusum* at Various Temperatures and Humidity Levels If two species in an ecosystem share overlapping fundamental niches, and one species dominates the other in all areas of the fundamental niche, the dominated species will not have a realized niche and will be competitively excluded from the entire ecosystem. Based on ecological theory, any species that wishes to survive in an ecosystem must have a realized niche that is distinct from those of all other species. ## Questions Based On Data: Competitive Exclusion in Cattail Plants *Typha latifolia* and *Typha angustifolia* are two species of aquatic plants that grow on lake edges. The top graph shows the primary production of each species when they grow together in a natural ecosystem. The bottom graph shows the biomass of transplants of the two species when grown without competition. Negative depths indicate growth above the water line. 1. Compare and contrast the growth of *T. angustifolia* and *T. latifolia* without competitors. 2. Distinguish between the growth of *T. angustifolia* with and without competition from *T. latifolia*. 3. Analyze the data in the graphs using the concepts of fundamental and realized niches. ## Figure 32: Competition Between Cattail Species ## Transversal Questions 1. What are the relative advantages of specificity and versatility? a. Summarize the role of specificity in enzyme function. (C1.1.7) b. Explain the evidence of evolution provided by the pentadactyl limb. (A4.1.4) c. Explain what is meant by the universality of the genetic code. (A2.1.7) 2. For each form of nutrition, what are the inputs, processes, and outputs? a. Explain what is meant by holozoic nutrition. (B4.2.4) b. Distinguish between the digestive mechanisms of organisms that eat detritus and saprophytes. (C4.2.12) c. Summarize an example of mixotrophy. (B4.2.5)