Community Ecology Revision EG1 PDF

Community ecology : Humbolt : demonstrating that the distribution of plant assemblages across the globe reflects climate. Haechel : define ecology like the science which studies the relationships between, organisms and the environment in which they live. Mobius introduce the concept of biocenosis :...

Community ecology : Humbolt : demonstrating that the distribution of plant assemblages across the globe reflects climate. Haechel : define ecology like the science which studies the relationships between, organisms and the environment in which they live. Mobius introduce the concept of biocenosis : interacting organisms living together in a habitat. Community ecology is a discipline historically very plant based. A discipline initially very descriptive which has become increasinlgy « explanatory ». It’s a discipline that requires naturalist skills. Population = set of infividuals of the same species, which occupy the same place at the same time. Community = set of populations of different species occupying the same place at the same time and interacting. Biocenosis = set of populations of all species occupying the same place, interacting Guild = set of populations of different species occupying the same place, and using the same ressources. What is the spatial limits of a community ? The organismic concept consider that there were clear and identifiable limits, so a « closed community » The individual concept consider that there is no spatial boundaries between communities, so it’s an open community. In reality we can observe obvious limit during an abrupt change in environmental conditions and sometimes quite clair limits even without a sudden change of environment. Concept of ecotone : transition between 2 zones. There is a lot of species in this edge zone (and species of different communities. The minimum area : is is the minimum surface area from which the plant composition can be considered representative of the community studies. For that purpose, what we can do is to study the first plot, then the second, if you find new species in the new plot, it’s that you surface is not representative. The minimum area correspond to the point where the number of species do not increase anymore even if the surface area has increased. At some time, by continuing increase the surface area, we will find new species, it’s the community boundary. Communities are identifiable on the ground, and identification is repeatable (same community in same conditions). Phytosociology : discipline whose aim is to describe and name plant associations. It’s an abstract concept grouping together all similar plant communities. There is different type of biotic interactions : Neutralism, predation, competition, mutualism, commensalism, ammensalism. Ammensalism = biotic interactions where one individual cause damage to another without benefit. The biological sampling in community ecology correspond to how to sample a plot to obtain a list of species and an assessment of the relative abundance of each species. The statistical sampling is : how many readings are needed, how do I distribuate the readings in space, should acontrol area be considered. There are varied methods of studying depending on the case of observation of the species of the taxonomic group studied. Floristic survey by quadrat : the surface of quadrat corresponding to the minimum area. I t allows the identification of all plant species and the estimation cover of each species. For forest, we need to make different plots, one for each stratum. There is also the floristic survey by line of contact points → indentify accross the line. Community metrics : Alpha = species diversity at the local scale gamma = species diversity on a global scale beta = difference in species composition between communities Measure of alpha : → species richness : number of species Species diversity take into account the species richness and the equitably of abundances. To way to calculate the species diversity : Shannon index : H’ pi = number of individual of a species on total number of individual of all species Simpson index : measure the probability that 2 individuals choosen at random belong to the different species. ni= number of individuals of species N = Total number of individuals of all species The shannon index is more sensitive to the richness components of species diversity. A high value of H’ means that there is a lot of different species. The simpson index is more sensitive to the equatibility component of species diversity. A high value of D means that the number of individuals in each species is equitable. One way to calculate the equatibility : The pielou index : Nearer to 1 the result of E is, the more equitable the community is. If not, it would significate that the community is dominated by a species. Rank frequency diagram : Reflects the species diversity, and allows you to visualize the structure of the community Application to conservation biology with care: 1) communities that may be poor in species of some taxon but rich in for others e.g. heathlands are rich in Orthoptera oak canopies are rich in insects in general 2) In some habitat types, communities are naturally poor in species: salt meadows, moors, heathlands. But these species grow nowhere else ==> contributing to high β diversity across landscape Here, high species richness is a bad sign. Measure of beta : difference in species composition between communities = degree of dissimilarity between communities Different way to calculate beta : The Jaccard index : it measure the similarity between 2 sets. Other commonly used indices make it possible to assess the (dis)similarity between 2 communities, in particular: → The Sørensen index , which gives double weight to shared species. It is like the Jaccard index, but we double the shared species. Limits : it don’t take into consideration abundance of species. → The Bray-Curtis index , which takes into account the abundance of species unlike the jaccard index who only take in consideration the presence or absence of species. When we want to compare more than 2 communities ? We calculate the dissimilarity of all possible pairs : distance matrix → The Whittaker index : Allows the evaluation of β diversity overall , for more than 2 communities. It measures how different or similar the species composition is between different habitats. A higher value means there is more species unique to individual site, the habitats are more distinct in terms of species compositions. 3,5 is the average species richness per community 14/4. We can also do Multivariate analyzes : Represents the similarity/dissimilarity between plots Construction based on distance matrices! Closer the points are, closer is the species composition in community Explaining diversity : filters : alpha diversity is low in some communities because strong filters hindering many species to esatblish beta diversity is high between some communities because different filters limiting establishment of species First, species dispersion depends on their ability to disperse (barriers etc). Second, the selection of species depends on their tolerance to abiotic stresses. To finish, species selection depends on their ability to cooperate with biotic pressures, including competition. The most species-rich communities are generally those with intermediate levels of stress. When the environment severity is low, we have a preponderance of the biotic filter, species are competitive. When environmental severity is high, we have a preponderance of the abiotic filter. In the case of invasive species, the dispersal filter is broke and we can have a release of biotic pressures : Two hypotheses: enemy release hypothesis →Species are introduced without their natural predators and pathogens evolution of increased competitive ability h’s →Introduced species invest energy in competiveness rather then enemy resistance. Invasive species invest more in growth, reproduction than in physical or chemical defense because they don’t have natural enemies in the medium. They can like this increase their competitivness. → using communities as bioindicators The individual in its environment See the world through the “eyes” of organisms, being able to interpret the traits of organisms Some terms : Resource : necessary for life, can be consumed or occupied, for example nutriment, mutualistes Contrainte : constrains life, cannot be consumed, for example heat or predator. How to respond to a constraint or an absence of ressources : - avoid (éviter) constraints in time or space - resist : be unaffected - tolerate : be affected, but manage (réussir) to survive Resource needs (les besoins de ressources), all the environnemental conditions necessary for the survive, reproduction growth of a species (for example resistance and tolerance to stress). All those conditions are find in the ‘physiological niche’ or ‘fundamental niche’. And the ‘ecological niche’ or ‘realizd niche’ that take in consideration interactions with competitors, mutualists, enemies. Resoure need and yhe ability to manage constraints vary between : - modules within an individual - ecotypes within a species (each ecotypes of a species are living in a different environnment) -species O2 / CO2 Effect : O2 : energy gain by oxidation of carbohydrates (respiration) CO2 : chemical storage of solar energy (photosynthesis) Distribution: of O2 A lot in the atmosphere, less on the soil, Distribution of CO2 : and less less deeper in the sea.  Gaz are more soluble in cold water, there is more dioxygen in cold water than in hot water. Response to a lack of O2/CO2 : avoidance →accessing air in « macrophytes » with aerenchyma : large aquatic plant have an aerenchyma. It’s a spongy tissu who contains ir channels that permits to efficiently transport dioxygen from above ground parts (such as surfaces leaves (feuilles)) to roots submerged in oxygen-poor sediments. This adaptation allows them to survive and grow in auqatic environments where oxygen is limited. → larvae of some insects : many larvae such as mosquitoes regularly rise to the surface of the water to directly capture atmopsheric oxygen. Avoidance /resistance → root hairs penetrating air pocket resistance → large exchange area (for example : gills (branchies) → meiofauna : Meiofaunal organisms, often small, have a large relative surface area. This allows them to exchange gases (O2 and CO2) more efficiently, even in oxygen-poor environments. → keep an air bubble → increase surface in exchange with the atmosphere tolerance → switch to anoxic respiration of sugars → shift to chemosynthesis : Chemosynthesis is a process by which certain organisms, such as some bacteria, create their own food using chemical substances instead of using sunlight. These organisms take inorganic compounds (like hydrogen sulfide or methane) and transform them into organic matter (like glucose) through chemical reactions. Chemosynthesis is often found in extreme environments, such as the deep ocean, near hydrothermal vents, or in nutrient-rich soils. → shift to the reduction of N : Nitrogen reduction refers to the conversion of atmospheric nitrogen (N2) into assimilable forms, such as ammonia (NH3), through biological processes. This process is essential for the nutrition of plants and microorganisms. In the absence of oxygen, some organisms can use alternative metabolic pathways to reduce nitrogen. This allows them to extract energy and nutrients more efficiently in anaerobic environments. The ammonia produced from nitrogen reduction can be used as a nitrogen source to synthesize amino acids and other biomolecules, enabling the organism to continue growing even when oxygen is limited. Heat : Effect : accelerated movement of molecules, biochemical reactions, metabolism and may also denaturalize proteins. Heat has a higlhy nonlinear effect : For example, a slight increase in temperature may stimulate metabolism, but excessively high temperatures can lead to protein denaturation and a collapse of biological functions Thermal balance : → of a leaf (une feuille) : → of an endothermic animal : In ecology : « evaporation » = loss of water vapor from soil and water, and « transpiration » is the loss from organisms. Distribution : example : a forest edge (lisière) during day (march 3, morning) At night, is less or more the opposite. There is also a distribution of the heat on the ground during the day, but also at the soil surface, and in a lake. → In spring, increasing air temperatures and longer daylight hours warm the surface of the lake. Heat concentrates at the surface, creating a warm layer of water (epilimnion) above a colder layer (hypolimnion) at the bottom. Between the two is a transitional zone called the metalimnion or thermocline, where the temperature changes rapidly. → In summer, the lake is usually strongly stratified. The epilimnion is warm (reaching 20-30 °C or higher), while the hypolimnion remains cold (generally below 10 °C). → In autumn Air temperatures begin to decrease, leading to the cooling of the lake's surface. When the surface water reaches about 4 °C, it becomes denser and starts to sink. This can trigger greater mixing, allowing heat to redistribute throughout the lake. Convection currents can occur, allowing oxygen to reach the depths and revitalizing the bottom layers of water. → In winter, cold climates, the surface of the lake may freeze. Ice, which is less dense than liquid water, floats on top, insulating the warmer water below (usually around 4 °C). An inverse stratification can occur, where the upper layer is colder (ice and surface water) and the warmer water is below. Response : → avoidance when it is too cold → migration Avoidance when it is to hot → local redistribution → resistance → for example thermoregulation Resistance when it is too cold : physiologically reduce freezing temperature (eg, decrease the quantity of water present in plant) Example : haemolymph : Without hemolymph, an insect would be less capable of withstanding cold temperatures. In the absence of these natural antifreezes and the other functions performed by hemolymph, the insect would be more susceptible to freezing quickly, which would lead to cellular damage and, ultimately, death. Produce its own heat, and keep it inside. Behavioral thermoregulation like migration, hibernation and dormancy, regrouping individuals to keep heat and reduce the loss of heat, chossing microhabitats (hide in dense vegetation for eg), changing posture. Behavioral thermoregulation/morphology Resistance when it is too hot : -reduce received radiation (hide under a tree) -increase convection : by increasing their leaf surface area or orienting their leaves to maximize contact with fresh air, which helps them manage heat. Many animals, such as birds, spread their wings or use flapping movements to create a current of air around them. Similarly, some mammals bathe in water or cover themselves with moist soil to increase convection and promote evaporation. Bergman’s rule : Bergmann's rule states that, generally, among similar species living in different climates, individuals from populations living in colder climates tend to be larger than those living in warmer climates. -increase relfection : With wite extension -increase transpiration : Sweating allows water to evaporate from the surface of the skin or membranes. As water evaporates, it absorbs heat from the skin's surface, leading to a cooling effect on the organism. This process is crucial for regulating body temperature in hot environments. → tolerance : thermotolerance Tolerance when it’s too cold : - frost tolerance - freezing tolerance Cells can adjust the concentration of solutes in their cytoplasm. When they lose water, they increase the concentration of various solutes (such as salts, sugars, or amino acids) inside the cells. This helps to balance the osmotic pressure between the inside of the cell and the outside, thereby minimizing water loss through osmosis. - diapause, passing into latent life : hibernation But also egg/seed (graines) : When it’s too hot, it’s difficult, passing into latent life : aestivation H2O Effect : 70 % of the body of most organisms, even terrestrial. Too much H2O = pas assez de O2/CO2. Here not enough H2O. Distribution : characterize the lack of atmospheric H2O by : realized H2O-pressure in atmosphere realized H2O-pressure in atm. / p’e.. at saturation = relative humidity A low relative humidity (close to 0) indicates a lack of water in the atmosphere, while a high value (close to 100) indicates a saturated atmosphere realized H2O-pressure in atm. - p’e.. at saturation = saturation deifict = water vapour deficit A high value of ΔP indicates a strong capacity of the atmosphere to hold water, suggesting a lack of humidity. In contrast, a low value indicates an atmosphere close to saturation. The saturation deficit (voir avec lenaïg) Water vapor is a powerful greenhouse gas. By increasing temperature, climate change raises the amount of water vapor in the atmosphere, which can, in turn, increase warming by trapping more heat. This cycle constitutes a positive feedback loop that intensifies climate change. ?? Lack of atmospheric H2O = heat + lack of water Lack of soil H2O = + precipitation – evapotranspiration * availability in the soil. We can characterize H2O available in the soil. The Permanent Wilting Point (PWP) is the soil moisture level below which plants can no longer extract water. This means that even if water is present in the soil, it is held tightly by soil particles, and roots cannot absorb it. At this stage, the water is considered unavailable to plants, leading to irreversible wilting if no additional water is supplied. The sable : low water retention because particles are large and allow water to drain quickly, resulting in a low level of water retention. Water availability for plants: Limited, as water moves quickly downward, often below the root zone. The silt (limon) : moderate water retention, Silt holds water relatively well, and the water is generally available to plants. The clay (argile) : very high water retention, Clay particles create a strong retention force, holding water very effectively, though sometimes too tightly for plants to absorb. Water availability for plants: Paradoxically low. Although clay contains a lot of water, some of it is inaccessible because it’s held too tightly for roots to extract. Response to a lack of H2O : Avoidance - avoidance of lack of atmospheric H2O--> avoid heat (see chapter on heat) - avoidance of lack of H2O in the soil--> behavior, e.g. of growth Plants may develop deeper roots(racines) to access water reserves further down (plus profondes), reducing their reliance (dépendances) on surface water. By limiting the growth of stems and leaves, plants decrease their evapotranspiration surface, thereby conserving water. y partially closing their stomata, plants limit water loss through transpiration, which helps retain moisture for longer. - life history : dormancy during dry period Resistance : increase acess to atmospheric water, and water in the ground, and reduce loss of water. To increase the access to atmospheric water : hygroscopy : absorb water vapor from an unsaturated atmosphere. To increase the access to water in the ground, we can increase root surface area by hair + mycorrhiza. We can also increase suction force by transpiration with modern vessels + tall foliage. When a plant transpires, it loses water through its leaves. This loss creates negative pressure in the vessels that transport water (the xylem vessels). It’s like the plant is "pulling" water from the soil up to its roots. By increasing this transpiration, the plant pulls harder on the available water in the soil. This allows it to extract moisture even when water levels are low, which is crucial during dry periods. Modern Vessels: Plants with well-developed and efficient xylem vessels (such as the conductive vessels in wood) allow for rapid and efficient transport of water throughout the plant, reducing losses and maximizing the use of available water. High Leaves: Plants with elevated foliage can capture more light and improve their photosynthesis, which stimulates transpiration. This is particularly important for tree species in forests, which can directly access light resources while maximizing transpiration capacity. To reduce the loss of water we can reduce the temperature and reduce the saturation deficit. When the temperature decreases, the air's ability to retain water vapor also decreases. This means that the amount of water vapor needed to reach saturation is lower at lower temperatures. When we decrease the saturation deficit, we increase the relative humidity. When the deficit of saturation is reduced, it can lead to the condensation of water vapor in the air, promoting cloud formation and, consequently, precipitation. Precipitation provides water directly to plants and soils, which is crucial during dry periods. We also need to reduce convection for example by depressed stomata, hairs, waterproof epidermis or cuticule. We can also close stomata during the day : photosynthesis by Crassulacean Acid Metaboliosm. Unlike most plants, CAM species open their stomata at night when temperatures are cooler and humidity is higher. This reduces water loss due to evaporation. During this period, they absorb carbon dioxide (CO₂) and store it in the form of organic acids, primarily malic acid. During the day photosynthesis continues by utilizing the stored CO₂, which is released from the organic acids when the stomata are closed. Throughout the day, CAM plants use sunlight to convert the stored CO₂ into glucose through photosynthesis. This allows these plants to continue producing energy while limiting water loss. Tolerance : -latent life : total reduction in metabolism -partial death + regrowth capacity Nutrients : example nitrogen (N) Effect : → AA → proteins → metaobolism, structure → DNA → Chlorophyll It’s the life Distribution : everywhere : 78 % of the air. But inaccesible because N2 other : organic matter (MO) and certain bedrocks (roches mères). But only what is mineralized as NO3/NH4 regional distribution : N input from agriculture, including gaseous (NH3) or N input from cars, including gaseous NOx local distribution : -litter -feces -layer of humus Response to a lack of N : by avoidance -root foraging behavior (comportement de fourrage des racines) : effective soil exploration, the development of lateral roots, the establishment of symbioses with microorganisms, and physiological modifications, plants maximize their ability to acquire the nitrogen necessary for their growth and survival. -colonization of post-disturbance locations with few competitors for N. by resistance : -increase N supply (l’apport en N) : N from the soil. We can do that by killing competitors, by allelopathy for example. Allelopathy is a biological phenomenon where a plant releases chemical substances into the environment—usually through its roots, leaves, or seeds—that influence the growth, survival, and reproduction of nearby plants. By ectomycorrhizas : Ectomycorrhizas are a type of symbiotic association between certain fungi and the roots of various plants, especially trees. In this relationship, the fungal (filament-like structures) form a sheath, or mantle, around the roots and extend into the surrounding soil, facilitating nutrient exchange between the fungus and the plant. -increase N intake : N2 from the air By Rhizobium bacteria (in Fabaceae) : In response to nitrogen (N) deficiency, certain plants have developed a resistance strategy to increase nitrogen intake through symbiotic bacteria capable of fixing atmospheric nitrogen, such as Rhizobium. This symbiosis is primarily found in the Fabaceae family (or legumes). Rhizobium bacteria penetrate the roots of host plants (legumes) and stimulate the formation of specific structures called nodules. Inside these nodules, the bacteria convert atmospheric nitrogen (N₂), which is biologically inert, into a plant-assimilable form (like ammonium, NH₄⁺). This process is known as biological nitrogen fixation. By Frankia bacteria (in Alnus) (same as Rhizo) By Cyanobacteria -increase N intake : N of organisms By carnivory : Drosera or Utricularia Capturing Prey: Sundews have leaves covered with glandular hairs that secrete a sticky, dew-like liquid capable of trapping insects that land on them. Digesting Prey: Once the insect is trapped, the plant’s glands secrete digestive enzymes that break down the insect, releasing nitrogen and other nutrients. Nutrient Absorption: The plant absorbs the nutrients from digestion, especially nitrogen, to compensate for the nitrogen-poor soils in its habitat By carnivory Capsella bursa-pastoris : seeds attract and digest nematodes to absord N from these nematodes. Helps to survive to nitrogen poor soils, or to difficult habitat. Some plants kill insects without actively digesting them. Insect pathogenic fungi : Certain plants establish a symbiotic association with fungi that infect and decompose insects in the surrounding soil. These fungi, often entomopathogenic (insect-killing), attack insects and break down their bodies. As the fungi decompose the insect, nitrogen and other nutrients from the insect's body become available in the soil. The plant can then absorb these nutrients through its root system. Parasitism : → reduce N loss : with perennial foliage for example. Plants keep there leaves few years, to decrease the loss of N. We can also remove N before leaf shedding. By tolerance : resource-conserving species. (see lecture on succession) Nitrogen – animals point of view Distribution : N2, NO3, NH4 unusable, only N in organic matter. N concentration : in plant litter (dead organic matter), N ratio of litter from different tree species And N concentration in living plant tissues (max pollen 14) vs needs in animals tissues, more than plants 3-7 Feces, 5-10 Concentration N/item Concentration item/landscape Opposite because there are more litters, leaves and seeds in nature than feces and animals. Accessibility : -indegistible molecules (cellulose, liginn) -molecules protected by indigestible envelopes: tannins, by toxins, by morphological structures, by counter attacks: animal behavior, parasitoids… -inaccessible organisms (“enemy free space”) ex.: under herbaceous veget’n, mice (souris) inaccessible for owls… -> without herbs: oak acorns (glands) inaccessible to mice (too much predation without herbs) Response to a lack of N by avoidance: use pollen or phloem or young leaves…. … thanks to morphological structures Pollen : pollen is rich in proteins, and therefore in nitrogen. Some plant divert their ressources to exploit pollen, and certains plants develop structures like nectar glands that attracts pollinators, allowing plant to benefit from N present in pollen carried by these insects. Phloem : the phloem tranpsort N from the leaves to other part of the plant. Plants develop finer roots or absorbent hairs that promote the uptake of N. Young leaves : they are highly concentrated in nitrogen, more than mature leaves, because young leaves actively growing and synthesizing proteins. To protect these leaves, plant develop structure like spines to make it difficult the access of predators too young leaves. Plants an use this thanks to very rapid development. By resistance : Animals can also eat more, digest better thanks to micro-organisms, increase resource concentration By tolerance : Starvarion capacity up to 300 days (capacité de famine)