Mapping and modeling species distributions Department of Botany and Zoology, Masaryk University Bi9661 Selected issues in Ecology, Autumn 2013 Borja Jiménez-Alfaro, PhD Part 2: MODELING THEORY BACKGROUND: the NICHE Adapted from: E. Martínez-Meyer, GBIF modelling workshop 2008 A. Guisan, W. Thuiller & N. Zimmerman, ECOCHANGE summer school 2009 THE NICHE Definition of niche in ecology 2) The function or position of an organism or population within an ecological community 1) The particular area within a habitat occupied by an organism The American Heritage® Dictionary of the English Language, Fourth Edition 2000 THE NICHE Wiens et al. (2010) Ecology letters 13: 1310-1324 Grinellian? Eltonian? Hutchinsonian? THE NICHE Niche is…. “…the ultimate distributional unit, within which each species is held by its structural and instinctive limitations” (1924). Joseph Grinnell (1916-28) Every species has its own physiological, morphological, and behavioral profile, which makes it suitable to occupy particular spaces offered by nature. THE NICHE He proposed a hierarchical classification of the environment that could be recognized as a measure of distributional control California Thrasher (Toxostoma redivivum) Food Breeding sites Refuges from predators Ecological or Environmental Niche Joseph Grinnell (1916-28) THE NICHE The niche is a property of the environment (not of its occupant): “…the ecologic or environmental niche… is occupied by just one species…if a new ecologic niche arises, or if a niche is vacated, nature hastens to supply an occupant…” (1924). Acknowledges the central role of interactions (Competitive Exclusion Principle):“No two species in the same general territory can occupy for long identically the same ecologic niche…” (1928). Similar niches are filled up with ecological equivalents. Joseph Grinnell (1916-28) THE NICHE “...[‘Niche’ describes] the status of an animal in its community, to indicate what is doing and not merely what it looks like...” Charles Elton (1927) The focus is on the functional role of species within the food chain. Abiotic conditions are not taken into account. “…the ‘niche’ of an animal means its place in the biotic environment, its relation to food and enemies.” THE NICHE The niche is a property of the biotic community (not of its occupant) – same principle as Grinnell Ecological equivalents are an indication of similar niches: “…we might take as a niche all the carnivores which prey upon small mammals, and distinguish them from those who prey upon insects…” The niche is not restricted to a single species: “There is often an extraordinarily paralell between niches in widely separated communities.” Charles Elton (1927) THE NICHE G. Evelyn Hutchinson (1944-58) Multi-dimensional niche THE NICHE “The term niche... Is defined as the sum of all the environmental factors acting on the organism; the niche thus defined is a region of an n-dimensional hyper-space...” (1944). G. Evelyn Hutchinson (1944-58) Ecological space THE NICHE Conditions in which species could feasible live are often greater than those where the organism actually lives, and this is typically caused by biotic interactions. Fundamental niche: all aspects of the n-dimensional hyper-volume in the absence of other species. Realized niche: the part of the fundamental niche to which the species was restricted due to interspecific interactions. G. Evelyn Hutchinson (1944-58) THE NICHE - The niche is a property of the occupant (not of the environment) – new concept ! - Niches have a temporal dimension - Competitive exclusion is part of the formalization:“…realised niches do not intersect” - Niches are mutable (i.e. evolve) G. Evelyn Hutchinson (1944-58) THE NICHE The niche became quantifiable because both: B) The internal structure of the niche is determined by the species’ performance (measured in terms of population fitness) A) Environmental variables could be expressed along continuos axes, and G. Evelyn Hutchinson (1944-58) THE NICHE A group of theoretical models designed to investigate how many and how similar coexisting species could be within a given community. Competition for resources is the primary underlying mechanism driving ecology Development of the niche theory (1966-84) Levins, MacArthur, Pianka, Roughgarden, Schoener, Colwell, May, Diamond The focus was on measuring: • Niche breath: the variety of resources/habitats used by a species • Niche partitioning: differential resource use by coexisting species • Niche overlap: mutual resource use by different species • Niche assembly: organization of species in new and abandoned habitats THE NICHE Decline of the niche concept (1981-2001) Connor, Simberloff, Lewin, Hubbell Major critiques: Lack of adequate null hypothesis and statistical rigor Competition is not necessarily the driving process in ecology Confusing and ambiguous use of the term ‘niche’ New conceptual frameworks (the so-called ‘neutral theories’) claim that the niche concept is unnecessary to understand fundamental, broad-scale patterns in ecology THE NICHE Reformulation of the Niche Concept “The niche of a species is the joint description of the environmental conditions that allow a species to satisfy its minimum requirements so that the birth rate of a local population is equal or greater than its death rate along with the set of per capita impacts of that species on these environmental conditions.” “The niche concept is important both as a tool for thinking about ecological and evolutionary phenomena and as a synthetic device for integrating these phenomena across levels of organizations [and scales] (e.g. individuals to ecosystems).” Chase and Leibold (2003) Ecological Niches: Linking Classic and Contemporary Approaches. University of Chicago Press THE NICHE Wiens et al. (2010) Ecology letters 13: 1310-1324 THE NICHE Guisan & Zimmerman 2000, fig. 3 THE NICHE The niche can be represented along few factors Ellenberg 1953 THE NICHE Causality of predictors in alpine plants THE NICHE Predictors for spatial modeling THE NICHE Niche and the SPATIAL prediction of species distributions Guisan et al. 2002 Ecological modeling THE NICHE What are we modelling? The so called Beta-niche SCALE: grid information at resolution of meters or kilometres DESCRIBING: niche attributes of species distribution across (scale-dependent) environmental and geographic gradients OUTPUT: raster models reflecting mean conditions in which species predictions are not exclusive (more than one specie can occur) THE NICHE What are we modelling, fundamental or realized niches? THE NICHE What are we modelling, fundamental or realized niches? THE NICHE Two main assumptions THE NICHE What are we modelling? – CONCLUSION Species distribution modeling (SDM) Environmental niche modeling (ENM) Using empirical data, biotic interactions and dispersal limitation are included if they area correlated with the predictors If this is true, we can assume than the model outputs reflect the realized niche, although we can not test it Different study cases have found evidences of Grinellian / Hutchinsonian niches, source-sink and dispersal limitations models