Download Specific research objectives

The evolution of dispersal traits at fragmented habitats
Current landscape is fragmented to a larger extent than it was in the past and
populations of most species thus tend to be isolated from each other (Saunders et al
1991, Hanski 1999). Survival and dynamics of species at such fragmented landscapes
is a topic of many recent studies (e.g. Wolf et Harrison 2001, Soon et Heil 2002). One
of the tools used for understanding determinants of species distribution at the
landscape scale is to explore traits of species at habitats, that are isolated and that are
not (e.g. Ellstrand et Ellam 1993, Ouborg 1993, Poschold et al. 2000). Results of these
studies often indicate that distribution of species depends mainly on species dispersal
ability such as ability to fly in the air, float in water, to disperse in bird digestion or in
bird feathers (Eriksson et Jakobsson 1998, Cain 2000, Dupré et Ehrlen 2002, Ozinga et
al. 2004).
It has also been shown that good dispersal ability itself does not always guarantee
successful dispersal. This is true especially in habitats where species persistence is
limited by nutrient shortage or high competition (Ehrlen et van Groenendael 1998). In
this case other traits such as seed size, seed number and competition abilities may be
more important for species distribution in fragmented habitats than dispersal traits of
the seeds (e.g. Leishman et al. 1995, Turnbull 1999, Ehrlen et Eriksson 2000,
Jakobsson et Eriksson 2000, Oifeng et al. 2000).
Recently, it has been shown that species distribution in a landscape is largely
determined also by the history of landscape (e.g. Dupré et Ehrlen 2002). Even large
and less isolated patches can have a small number of species if the period of migration
is limited. But the opposite extreme is also possible – patches can have more species
than we would expect to their size and isolation. Thus the distribution of species in
such systems having variable history might depend more on the time since their last
change than on parameters of the locality. The traits identified as traits allowing
species to disperse and survive at fragmented habitats may thus be in fact traits
associated with longevity that guaranty that the species did not yet go extinct at that
locality.
Conclusions of the recent studies concerning the importance of plant traits for their
distribution in landscape might thus be limited by the fact that distribution of species
in the landscape is not in equilibrium. That is why we still do not know the long-term
consequences of landscape fragmentation for species distribution and do not have a
good knowledge of the traits responsible for this distribution. Also we do not know
much about evolution of traits related to species dispersal ability and survival of
species at fragmented habitats to understand the ability of species to adapt to such
fragmented habitats. To study this we need to explore distribution of species and their
traits at habitats that have remained relatively stable over long time periods.
Ideal systems for such study are islands, i.e. systems that have been fragmented and
isolated for a long time period. Here the species distribution is relatively in equilibrium
and has resulted from species dispersal over long time span (Emerson 2002). The longterm isolation, plenty of unoccupied space and free niches are also ideal conditions for
evolutionary processes such as adaptive radiation giving rise to many new taxa, which
have adapted to the wide range of environments (Crawford et al. 1997). Other fact
contributing to the high rate of evolution of species is that the environment on islands
has not changed much since the rise of islands, while on mainland further evolution of
species can be limited by repeated changes of landscape (Barton 1996).
Thanks to their isolation the colonization of newly emerged islands is limited to
species dispersed by air, water and birds, which are able to get over distances between
mainland and island (Ridley 1930). Well dispersed species might have higher chances
to colonize newly established places, but long-term persistence on islands requires also
an ability of species to keep on their places which they have colonized and to be able
to reproduce (Carlquist 1974, Ehrendorfer 1979, Fernández-Palacios et Andersson
1993). This can lead to the successive loss of dispersability as shown in big groups of
insular species in Hawai (e.g. Bidens – Scherff 1937, reviewed by Carlquist 1974).
Species on islands are thus expected to confront two requisites – to disperse (to
colonize an island) and not to disperse (not to fall into the sea and to persist on
locality). Therefore, we can expect two groups of species with different life strategies
on islands: species which are able to disperse and which occur also on mainland from
where they migrated to islands and insular endemic species dispersing only among
islands. While the first group of species has not yet been so much influenced by
evolution and may have kept their original traits, the second group has passed bigger
evolutionary changes. By comparing traits of these groups it should thus be possible to
identify traits, that have a potential to evolve in a new habitat and those, that are very
conservative and cannot change over time.
For identification of the ability of species to cope with habitat fragmentation it is also
important to know how fast the species traits can evolve. Ideal systems for such study
are large groups of closely related species that have originated by adaptive radiation.
By adding their dispersal traits to their phylogenetic trees it is possible to observe,
which traits arose repeatedly and independently on various phylogenetic levels and
which traits arose only once. This enables to investigate how fast a trait can evolve and
predict, which traits can have potential to change due to landscape fragmentation and
which do not. The possibility of such studies has been opened just very recently with
the extensive development of molecular techniques and resulting increase in number
of published phylogenies (e.g. Kim et al. 1999 , Park et al. 2001Emerson 2002, Pfosser
et al. 2003).
Observing evolution of traits by comparisons to phylogenetic trees has been
successfully applied to other ecological studies (Paradis et Claude 2002) such as those
dealing with patterns of reproductive allocation or plant defensive mechanisms and
helped to clarify that variation in these patterns need not be caused by different
ecological factors as previously thought, but different plant life histories (e.g.
Donoghue et Ackerly 1997, Silvertown et Dodd 1997, Ackerly et Nyffeler 2004,
Johnson et al. 2003). This approach has, however, not yet been used to explore
evolution of traits related to species dispersal ability and survival over a wide range of
species.
The comparison of phylogenetic trees provides information on possibilities of trait
evolution over relatively long time periods through speciation. For applying the
knowledge to species performance in fragmented landscapes it is, however, necessary
to understand species evolution also at shorter scales within a single species. Such
information can be obtained from studying insular and mainland populations of the
same species.
Ideal systems for exploring these issues are the Canary Islands. These islands are
suitable for this study for several reasons: it is a system of volcanic islands which have
never been connected with continent, thus their species must have evolved from
ancestors, which had migrated to islands. The islands differ in size and age. Different
times of their arises create unique natural transect in time. There is also a relatively
good knowledge of phylogenies of many species groups of Canary flora (Stevens
2002, Mort et al. 2002, Fairfield et al. 2004, Lee et al. 2005) and their source mainland
regions (Sunding 1979).
Thanks to the fact that canary flora has been well studied, the origin of almost all
species is well known. There is thus relatively good knowledge of which species got to
the islands before arrival of human and which species arrived to the islands as a result
of recent human activities. Furthermore, Canary Islands are still relatively close to the
mainland and are also relatively old, so species invasions are not as extensive as in
other island systems (e.g. Hawaiian islands, Price 2004).
Besides this, Canary Islands provide good study background for performing such
study. Most importantly this project will be done in cooperation with the Botanical
Garden in Gran Canaria. Here we can use the extensive collection of the native flora in
the garden. We will also have an opportunity to closely collaborate with many local
experts and thus have access to recent information that is sometimes difficult to find in
the libraries elsewhere.
BASIC SCIENTIFIC AIMS
 Identify short and long term evolutionary dynamics of traits related to dispersal
ability and growth dynamics within groups of closely related species.
 Identify selection pressure on dispersal traits on islands.
 Identify dispersal traits that are prerequisite for successful colonization of island
habitats.
SPECIFIC RESEARCH OBJECTIVES
 Compare traits related to species dispersal between endemic and non-endemic
closely related species and use it to identify traits which the species possessed
when colonizing the islands and which traits evolved just after species
dispersion on islands.
 Explore, how these traits are changing along phylogenetic trees of selected
groups of species, to identify long-term evolutionary dynamics of these traits.
 Investigate differences in traits between insular and non-insular populations of
the same species occurring both on islands and mainland, to identify short-term
evolution of these traits.
 Compare dispersal traits between species occurring on one island to species
occurring on more islands, but preferring same type of habitat, to find traits,
which predetermine abilities to disperse among islands.
 Compare dispersal traits between species occurring both on islands and
mainland to species occurring only on mainland but preferring same
environmental conditions, to find traits, which predetermine abilities of species
to colonize islands.
These questions will be studied on species from Canary Islands and closed mainland
(the Meditterranean area). Besides reason mentioned above Canary islands provide a
wide range of vegetation types with species which are common both in Macaronesia
and the Meditterranean, as well as large number of species endemic for Canary islands
(about 25% of all canary species, Machado 1998). There is also relatively high
variation in occurrence of species among islands.
Data to be collected
Measuring species traits
For each species we will collect seeds and measure parameters connected with their
ability to disperse by wind (anemochory), in salt water (hydrochory), in bird digestion
(endozoochory) and in bird feathers (exozoochory).
To identify traits related to seed production and germination ability of seeds we will
measure weight of seeds, seed production per plant, seed production per unit area of a
stand and percentage germination of the seeds in laboratory conditions.
Seed production per plant and per unit area will be measured for at 3 localities for each
species.
Seed production per plant will be measured as average number of seeds per fruit
multiplied by average number of fruits per individual. Seed production per unit area of
a stand will be the result of multiplying of seed production per plant and average
number of plants per square meter. We will choose areas with higher species canopy.
To identify the ability to disperse by wind (anemochory) we will measure terminal
velocity of seeds (by measuring the rate of falling of seeds from defined height and
measuring length of seed flight, Tackenberg 2001). For this experiment we will collect
30 seeds per species from 3 localities (10 seeds from each locality), in the case of
species from the garden we will use 10 seeds. We will also measure plant height of 10
randomly chosen plants at 3 localities for each species in the field; the final height will
be arithmetical mean of measured values. We will then express the mean dispersal
distance of seeds by wind as a product of terminal velocity, wind speed and plant
height. Wind speed will be a constant value for all the species.
To identify the ability to disperse in salt water (hydrochory) we will measure
buoyancy of seeds defined as time over which seeds are able to keep floating on water
surface. In the case of seeds collected from the field we will use 150 seeds per species
from 3 localities (50 seeds from each locality), for seeds gained from the garden we
will use 50 seeds per species in this experiment. Seeds will be put into bins filled with
salt water and then stirred around in these intervals: 2, 17, 24 hours, other stirring will
be after 7,14,21,28, 35 days. Before each stirring the number of sunk seeds will be
counted. Seeds, which will keep floating to the end of experiment, will be tested for
germination (Boedeltje et al. 2003).
To study endozoochory (the ability to disperse in bird digestion) we will simulate
processes (mechanical and chemical digestion) in bird digestive tract. Mechanical
digestion in bird struma will be simulated by seed or fruit crashing with small stones.
As analogy to chemical digestion seeds will be dipped in 1M H2SO4 for 1-2 hours.
Undamaged seed will be tested for germination (Santamaría et al. 2002). We will use
60 seeds per species colleted from 3 localities (20 seeds per locality), in the case of
species from the garden we will need 20 seeds per species.
To study exozoochory (the ability to disperse in bird feathers) we will use stuffed bird
that will be rolled out in a certain number of seeds or fruits from each species. After
counting a number of seeds, which have attached to feathers, the bird flight will be
simulated and then a number of attached seeds will be counted again. We will use 90
seeds per species from 3 localities (30 seeds from each locality) or 30 seeds per
species collected from the garden. Another possibility how to observe exozoochory is
to use real bird trained for carrying messages (e.g. pigeon).
Studied species and types of analyses
Different species and species groups will be selected to answer different questions.
The selected species and types of analysis are thus provided separately for each of
them.
1/ Comparing traits between endemic and non-endemic species
According to Hohenester et Weiss (1993) and Bramwell et Bramwell (1974) we will
select group of genera including species endemic for Canary Islands and species
occurring both on islands and mainland (especially in Marocco and in the
Mediterranean, i.e. the areas from which most of the species in Canary islands
originated – Sunding 1979). The candidate genera include genus Salsola, Polycarpaea,
Hypericum, Echium, Sonchus, Helianthemum, Asteriscus, Tolpis, Euphorbia,
Limonium, Artemisia, Scrophularia, Asparagus, Phagnalon. We plan to select at least
40 species pairs. The specific selection will still be adjusted after consultations with
botanists from The Canary Botanical Garden and will also depend on the possibility to
collect sufficient number of seeds of the species. The seeds of the selected species will
be collected, and their traits related to dispersal will be measured. The majority of
seeds can be obtained from the Canary Botanical Garden; the rest of them will be
collected directly from the field.
Types of analyses: to compare differences between traits of endemic and non-endemic
species we will use ANOVA. Each trait will be tested separately; effect of species
pairs will be filtered out. For testing the relationship between traits we will use PCA in
CANOCO for Windows 4.0 (ter Braak et Šmilauer 2002).
2/ Changes of traits during phylogenies of species
In this case taxa with larger number of species with well-known published phylogenies
(e.g. Lotus, Pericallis, Echium, Argyranthemum, Sonchus, Tolpis, Asparagus) will be
selected. Then dispersal traits of these species will be compared to their phylogenetic
trees. This enables us to study how these traits have changed during phylogenies and
to identify the direction of trait development.
Types of analyses: To identify changes in species dispersal traits during their
phylogenies we will first count number of changes in each trait along each
phylogenetic tree. For testing differences between species we will use generalized
estimating equations (GEE, Paradis et Claude 2002). The phylogenetic relationships
among species will be taken into account with correlation matrices as distances among
species measured on phylogenetic tree. Correlation matrices will be incorporated into
GLM analyses of traits.
3/ Differences between insular and mainland populations of species
For this type of question we will choose only non-endemic species occurring both on
islands and mainland. Besides some species mentioned above we consider these
species: Traganum moquinii, Bassia tomentosa, Neurada procumbens, Zygophyllum
fontanesii, Astydamia latifolia, Heliotropium erosum, Helianthemum canariense,
Sonchus pinnatifidus, Andryala glandulosa, Scilla latifolia, Coronilla viminalis,
Salsola vermiculata, Ifloaga spicata. Specifically, we plan to select at least 20 species.
Species, which have recently been introduced to islands, will not be included.
For each species we will choose at least 3 insular and 3 mainland populations. All
these seeds will be collected in natural populations. Besides dispersal traits, individual
growth rate and plasticity will be studied in these species. By studying growth rate it
will be possible to find differences in dynamics of insular and mainland populations
and to compare, which of them has higher turnover. Plasticity experiments will show,
to what degree species are able to adapt to variation in environments.
To identify individual growth rate we will grow species from seeds in greenhouse
condition and measure their development over a give time period (approx. 1 year).
Plasticity will be studied by growing these species in different conditions and
observing how these conditions influence species traits. Conditions used in this
experiment will simulate the main gradients on islands, especially moisture and light
intensity gradients.
Types of analyses: To identify differences between insular and mainland populations
we will use ANOVA/GLM. The effect of species will be used as a covariate. We will
estimate the proportion of variation in each trait that can be accounted for by source of
population (island/mainland) and what proportion can be explained by variation
between populations within source.
4/ Traits predetermining the ability of species to disperse among islands
The question concerning traits predetermining the ability of species to disperse among
islands demands to compare species composition among islands. This type of
information will enable us to predict which traits are associated with species absence
from island. Because of the species specific demands on environmental conditions
correction on abiotic factors will be necessary. Thus we will select such groups of
species growing on the same type of habitat occurring on all of analyzed islands.
This type of correction will enable us to distinguish between species absent from
islands due to unsuitable conditions and due to the fact that it has not got there yet. For
this purpose we will choose groups of phylogenetically related species, which will
differ in occurrence among islands (from one island to more or all islands). We will
consider species of these genera: Aichryson, Monanthes, Pericallis, Lotus, Crambe,
Aeonium, Tolpis, Polycarpaea, Euphorbia, Sideritis.
Types of analyses: To identify traits predetermining the ability of species to disperse
among islands we will compare traits among species to their occurrence on islands.
For this analysis we will use ANOVA and filter out the effect of genus. In the case that
species are not selected according to genera (due to small number of species per
genus) we will analyse more species irrespective of genus. We will also consider the
age of islands as a factor influencing species presence on island.
5/ Traits predetermining the ability of species to disperse on islands
In the case of studying the ability of species to disperse on islands comparisons will be
made between species occurring both on islands and mainland and species growing
only on mainland. Other aspect of species selection will be that compared species will
grow on the same type of habitat. This correction will resolve differences in species
traits caused by different conditions at different types of habitats. Selected species will
belong to these genera: Limonium, Lotus, Sonchus, Echium, Crambe, Hypericum,
Helianthemum, Artemisia, Ononis, Plantago, Senecio.
Types of analyses: To identify traits predetermining the ability of species to disperse
on islands we will test differences between traits of species growing on mainland and
island and species growing only on island. For such testing we will use ANOVA,
effects of species pairs will be filtered out.
Time schedule:
Final selection of species and collecting their seeds will already start in 2006 i.e.
before initiation of this project. It will thus be possible to finish all the work within 3
years of the project.
Collecting seeds of selected species in the Canary Islands, measuring of parameters
connected with dispersal and germination abilities and seed production – 1
Selection of populations of species growing on islands and mainland, collecting their
seeds – 1
Greenhouse experiments with growing species from seeds collected from insular and
mainland populations, measuring growth rates and plasticity – 2
Collecting seeds of species growing both on island and mainland and species occurring
only on mainland – 2
Analysis of collected data – 2,3