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Presentation on theme: "SPECIALISTS AND GENERALISTS IN SPACE. HOW CAN WE DISTINGUISH GENERALISTS FROM SPECILISTS? - Able to thrive in a wide variety of environmental conditions."— Presentation transcript:


2 HOW CAN WE DISTINGUISH GENERALISTS FROM SPECILISTS? - Able to thrive in a wide variety of environmental conditions. - Has a variety of different resources. GeneralistSpecialist - Able to thrive in a narrow range of environmental conditions. - Has a limited diet.


4 Here we have Puya raymondii which is found in the altoandina zone of Bolivia and Peru and, from 3200 – 4800 m above the sea level. Here we have Ficus benjamina which is a native plant from Asia to Australia. It has high tolerance to different growing conditions. From temperate to very warm environments.

5 Under a kind of change on the medium like an a environmental change. Generalists species will be able to adapt and survive And specialists will tend to fall victim to extinction much more easily

6 WHAT WE NEED TO KNOW IS… that most of the organisms do not fit neatly into either group. Why? Definition of specialists or generalists may change depending on the context: -Species requirements -Biological level (individual, species, population or community). -At different spatial scales. As a consequence sometimes it is complicated to define the limits between both specialists and generalists. So, for trying to understand this lets focus in specialization’s definition, which in fact is still complicated to define ;(

7 SPECIALIZATION: Is inferred indirectly from species (Calenge & Basille 2008) -Distribution. -Environmental data. -Species performance. THE QUANTIFICATION: Is highly dependent on (Devictor et al 2010): -Data used -Organisms studied -Ecological mecanisms of interest.

8 A LITLE BIT OF HYSTORY -Levins (1968). The concept is useful to predict adaptive response of populations in heterogeneous and/or fluctuating environments. -Futuyma & Moreno (1988). It is needed to clarify the term from the classical distinction between the fundamental niche of a species and its realized niche. -Tomson et al. (1996). Species might be found in unsuitable habitats because of source sink dynamics or be absent from suitable habitats because of dispersal limitation.


10 What is niche? Grinell (1917). Hyper volume in multidimensional space of ecological variables within which species can maintain a viable population. Elton (1927). n- dimensional functional space, measured as species position along axes, embodying functional attributes rather than resources variables. This perspective of niche has been used for trying to understand specialization definition. Grinellian’s perspective: what do species need? Biotic and abiotic recourses determine distribution and abundance of them. It is measured using species requirements. Eltonian’s perspective: what species do? It refers to position of them in the envirorment. It is measured as species breadth of functional roles.

11 From a GRINNELLIAN’s perspective

12 Gibbes and Barrett (2011). Diet Resource Partitioning between the Golden Mouse (Ochrotomys nuttalli) and the White-footed Mouse (Peromyscus leucopus) Question: How Peromyscus leucopus and Ochrotomys nuttalli, with extreme niche overlap can coexist without manifesting patterns of interference or exploitation competition? For these they measured differences in diet preferences and caloric intake among 5 diets. The Methods: -The laboratory work was in Georgia in winter the 2006 and They used 5 kind of food both species normally consume in their habitat. -They used 5 thanks for each kind of food for the observations. -The observations were during 10 days. They species they used: Cornus florida (flowering dogwood), Ligustrum sinense (chinese pivet), Quercus nigra (water oak), Quercus alba (white oak), Rhus typhina (staghorn sumac)

13 Fig. 1. Bar diagram (6SE) illustrates the dietary ranking for both species expressed as mean caloric intake (Kcal N g live wt21 N day21). Different letters above bars show significant differences (P # 0.05) among diets. They conclude: P. leucopus, is considered a habitat generalist species, exhibited a wider dietary breadth and greater caloric intake than O. nuttalli, considered a habitat specialist species.

14 There is something important that we need to know about these both perspectives Specialization could be: -An intrinsic character of the species. -An contingent character that depends on the biotic or abiotic environment. Fundamental Realized

15 Barnagaud et al. (2011). When species become generalists: on-going large-scale changes in bird habitat specialization. Question: Is specialization to habitat openness a fixed trait in the short term? The Methods: -The work was in France from 2002 – They worked in 8 kind of habitats ordered by composition and structure of the forest, from mature to open areas (8 classes). They employed an index named SSI, which assumes that the more abundant a species is in certain habitat classes with respect to the other classes, the more specialized it is. SSI of a given species i at year j is the coefficient of variation of its densities across the k habitats considered (k = 8 in this case)

16 Fig. 1. (a) Temporal trend in the Species Specialization Index (SSI) and (b) variation of the SSI respective to log-transformed density. Grey lines in (a) represent the variations of species SSI across the period. Each point in (b) corresponds to a species in a given year. Plain black lines and associated dashed black lines are the estimates of the linear models SSI = f(years) (a) and SSI = f(log(density)) (b) 1.96 SE. They conclude: Habitat specialization is a labile ecological trait, which may change in the short term following habitat degradation, density dependence and source–sink dynamics.


18 The way how specialization is defined is going to be related to scale considerations that are taken for the sampling method: 1.If we maintain the scale of observations. specialization to any ecological factor can be equally specialized at larger spatial scales. 2.If we increase the scale of observations, we will increase the number of resources present and used. So the breadth of functional roles of specialists may change from local to larger scales.

19 So, the definition can change depending on the ecological spatial scale (Wiens et al. 1996)

20 Commelina virginica Biogeographically is distributed only in America and prefers moist soils. The Humboldt penguin Regionally is distributed only along t he Humboldt Current.

21 Fine et al Herbivores Promote Habitat Specialization by Trees in Amazonian Forests. Question: Can soil specialists grow in a different edaphic environment, or is soil type alone a sufficient barrier for these plants? The Methods: -The work was in Peru from 2001 – They worked in 2 kind of habitats. Clay soils and white sand soils -They used 880 seedlings corresponding to 6 genera and 20 species. They meassured growth rate (leaf area and height) and mortality. Amazonian trees Locally present in only in white sand forests.

22 Fig. 1. The effects of habitat and herbivore protection on (A) leaf area growth rate, (B) meristem height growth rate, and (C) percent mortality for white-sand and clay specialist species. Bars represent mean and 1 SE. Values with different letters (a, b, and c) are significantly different from one another [Tukey tests for (A) and (B); Mann- Whitney U for (C)]. They conclude: Habitat specialization in this system results from an interaction of herbivore pressure with soil type.

23 Conclusions. In general, to define an organism as a specialist r as a generalist someone is conditioned by: -Spatial and temporal fluctuations in the environmental conditions and in the interaction between species. -Local genetic adaptations. -Phenotypic plasticity of individuals. -The sampling design if environmental conditions are over the population of interest.

24 1. Robledo & Horvitz Experimental demography and the vital rates of generalist and specialist insect herbivores on native and novel host plants. 2. Fenesi et al Hard traits of three Bromus species in their source area explain their current invasive success. 3. Fine et al Herbivores Promote Habitat Specialization by Trees in Amazonian Forests.

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