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Population and community ecology 2 © Zanichelli editore 2015

Population ecology 3 © Zanichelli editore 2015

The study of ecology 4 It is possible to study ecology at different levels. From the micro to the macro levels, there exists: organism; population; community; ecosystem; biosphere. Ecology is the study of interactions among organisms and their relationship with the environment. © Zanichelli editore 2015

Ecology concepts: the habitat 5 Every organism presents two defining characteristics that define it: habitat and niche. The habitat is the particular environment in which an organism lives. © Zanichelli editore 2015 The tropical forest is a habitat for thousands of plants, insects and birds.

Ecology concepts: the niche 6 A species’ niche is the set of physical and biological conditions it requires to survive, grow, and reproduce. A niche is therefore partly defined by the resources available in the environment. © Zanichelli editore 2015 A plant’s niche includes how much direct sunlight it can tolerate and the type of soil on which it thrives; for an animal, niche involves elements such as the food it eats and whether it is active at night or during the day.

Describing a population 7 A population is a group of individuals of the same species living in a habitat for a relatively long period. Populations can be described using the following aspects: the size – the number of individuals in the population; the density – the number of individuals per unit area; the distribution in the environment – the pattern of dispersal of individuals across the area; the age distribution – the number of individuals in different age groups. © Zanichelli editore 2015

Population dynamics 8 Demography is the study of changes in a population’s density and structure – also known as population dynamics. Birth and death rates are the main factors influencing changes in the size and structure of a population, along with migration. © Zanichelli editore 2015

Patterns of population growth: exponential growth 9 Exponential growth is a type of population growth that accelerates over time. It is typical of conditions with unlimited resources and no limiting factors. © Zanichelli editore 2015

Patterns of population growth: logistic growth 10 Logistic growth occurs when the density of a population reaches the carrying capacity of the environment; growth slows down, resulting in an S-shaped curve. It is influenced by limiting factors. © Zanichelli editore 2015

Density-dependent factors affect population size 11 Population size can be influenced by factors that depend on how many individuals from that population live in a given habitat; these are density- dependent factors, such as competition, predation and parasitism. In these cases, mortality increases as the density of the population increases. © Zanichelli editore 2015

Density-independent factors affect population size 12 Also abiotic factors, like hurricanes, floods and fires, can influence population size; these are density-independent factors, which are not influenced by population dynamics. In these cases, mortality does not depend on density. © Zanichelli editore 2015

Life history patterns: r-strategy species 13 In order to survive in different environmental conditions, species adopt different strategies. Opportunistic species (r-strategist) Exponential population growth followed by periodic falls in population size; Small individuals with short life spam; Many offspring, but with relatively low probability of surviving to adulthood. © Zanichelli editore 2015

Life history patterns: K-strategy species 14 Equilibrium species (K-strategist) Logistic population growth; Larger individuals with long life spam; Fewer offspring, but with relatively high probability of surviving to adulthood. © Zanichelli editore 2015

Life history patterns and the environment 15 Opportunistic species, like rabbits and dandelions, are adapted to a fluctuating environment. Equilibrium species, like gorillas and oaks, are adapted to a relatively stable environment. © Zanichelli editore 2015

Community ecology 16 © Zanichelli editore 2015

Interactions of populations in a community 17 A community is an assemblage of populations of different species, living in the same area and interacting with each other and with the environment. There are different types of interactions: competition predation parasitism mutualism commensalism © Zanichelli editore 2015

Competition 18 Competition occurs when two or more species use the same resource. The result of competitive interactions depends on the availability of the resource. According to the competitive exclusion principle, no two species can occupy the same ecological niche at the same time. Resource partitioning decreases competition between two species. © Zanichelli editore 2015

Predator-prey interactions /1 19 Predation occurs when individuals of a species (predators) feed on individuals of a different species (prey). Predator-prey interactions affect the dynamics of both populations: more predators result in fewer prey; when the number of prey declines, predators decrease too and prey increase again. More predators Fewer prey Fewer predators More prey © Zanichelli editore 2015

Predator-prey interactions /2 20 © Zanichelli editore 2015 Prey have evolved defences to escape predators: senses, speed, protective body parts, and chemicals. Some species are able to deceive predators by camouflage, cryptic coloration, and mimicry. Camouflage of a Shield Mantis (also called Leaf Mantis) in the Peruvian Amazon.

Parasitism 21 © Zanichelli editore 2015 In parasitism, a population receives benefits at another’s expense. It occurs when individuals of a species consume only part of the tissues of individuals of another species, usually without killing them. Some parasites are pathogens and they cause a disease in the host. Monotropa uniflora, also known as the ghost plant, does not contain chlorophyll. Instead of generating energy from sunlight, it is parasitic to some mycorrhizas.

Commensalism and mutualism 22 Commensalism benefits one species without causing damage to the other. For example, scavengers have a commensalistic interaction with some predators. Mutualism is an interaction between species that results in benefits for both. Pollination is a typical example of mutualism between the plant and the pollinator. © Zanichelli editore 2015

Ecosystem ecology 23 © Zanichelli editore 2015

Ecosystems 24 Ecosystems are composed of: Biotic components – living organisms; Abiotic components – - resources, like sunlight and nutrients, as well as conditions such as soil, water, temperature and wind. © Zanichelli editore 2015

Trophic structure of the ecosystems 25 The trophic structure of an ecosystem describes the food relationships inside a community. It presents different trophic levels, that when taken together, form a food web. © Zanichelli editore 2015

Flux of energy through ecosystems 26 The main source of energy for the Earth is the Sun. In the flux through different trophic levels, energy is consumed and dissipated in the form of heat. Primary producers: autotrophs Primary consumers: herbivores heterotrophs Secondary consumers: carnivores heterotrophs Tertiary consumers: carnivores that feed on other carnivores © Zanichelli editore 2015

27 Chemical nutrients, like energy, pass from one trophic level to the next until decomposers return them to the environment where producers can take them up again. Unlike energy, matter does not dissipate. Chemical cycling through ecosystems © Zanichelli editore 2015

28 An ecological pyramid is the graphic representation of the number of organisms, biomass or energy, content of trophic levels. © Zanichelli editore Ecological pyramids Producers Primary consumers Secondary consumers Tertiary consumers