Transcript Document

SPECIALISTS AND
GENERALISTS IN SPACE
HOW CAN WE DISTINGUISH GENERALISTS FROM SPECILISTS?
Generalist
Specialist
Able to thrive in a wide
variety of
environmental
conditions .
- Able to thrive in a narrow
range of environmental
conditions.
- Has a variety of different
resources.
- Has a limited diet.
ESPECIALIST
GENERALIST
Here we have Puya
which is found in the
zone of Bolivia and
from 3200 – 4800 m
sea level.
raymondii
altoandina
Peru and,
above the
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.
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
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 ;(
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.
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.
HOW SPECIES BEHAVE IN THE ENVIRONMENT?
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.
From a GRINNELLIAN’s
perspective
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 2009.
- 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)
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.
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
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 – 2008.
- 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)
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.
HOW SPECIES ARE DISTRIBUTED IN THE SPACE?
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.
So, the definition can change
depending on the ecological spatial
scale (Wiens et al. 1996)
Commelina virginica
Biogeographically is
distributed only in
America and
prefers moist soils.
The Humboldt penguin
Regionally is
distributed only along t
he Humboldt Current.
Amazonian trees Locally present
in only in white sand forests.
Fine et al. 2004. 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 – 2003.
- 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.
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.
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.
1. Robledo & Horvitz 2011. Experimental demography
and the vital rates of generalist and specialist insect
herbivores on native and novel host plants.
2. Fenesi et al. 2011. Hard traits of three Bromus species
in their source area explain their current invasive
success.
3. Fine et al. 2011. Herbivores Promote Habitat
Specialization by Trees in Amazonian Forests.