GENETIC EROSION

Genetic erosion is a process whereby an already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die off without getting a chance to meet and breed with others in their endangered low population. The term is sometimes used in a narrow sense, such as when describing the loss of particular alleles or genes, as well as being used more broadly, as when referring to the loss of varieties or even whole species.

Genetic erosion occurs because each individual organism has many unique genes which get lost when it dies without getting a chance to breed. Low genetic diversity in a population of wild animals and plants leads to a further diminishing gene pool – inbreeding and a weakening immune system can then "fast track" that species towards eventual extinction.

All the endangered species of the world are plagued to varying degrees by genetic erosion, and most need a human-assisted breeding program to keep their population viable, thereby avoiding extinction over long time frames. The smaller the population is on a relative scale, the more magnified the effect of genetic erosion becomes, as weakened individuals from the few surviving members of the species are lost without getting a chance to breed.

Genetic erosion also gets compounded and accelerated by habitat fragmentation - today most endangered species live in smaller and smaller chunks of (fragmented) habitat, interspersed with human settlements and farmland, making it much more difficult to naturally meet and breed with others of their kind, so many die off without getting a chance to breed at all, and thus are unable to pass on their unique genes to the living population.

The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection. Meanwhile, low genetic diversity (see inbreeding and population bottlenecks) can cause reduced biological fitness and increase the chance of extinction of that species or population.

Processes and consequences

Population bottlenecks create shrinking gene pools, which leave fewer and fewer fertile mating partners. The genetic implications can be illustrated by considering the analogy of a high-stakes poker game with a crooked dealer. Consider that the game begins with a 52-card deck (representing high genetic diversity). Reduction of the number of breeding pairs with unique genes resembles the situation where the dealer deals only the same five cards over and over, producing only a few limited "hands".

As specimens begin to inbreed, both physical and reproductive congenital effects and defects appear more often. Abnormal sperm increase, infertility rises, and birthrates decline. "Most perilous are the effects on the immune defense systems, which become weakened and less and less able to fight off an increasing number of bacterial, viral, fungal, parasitic, and other disease-producing threats. Thus, even if an endangered species in a bottleneck can withstand whatever human development may be eating away at its habitat, it still faces the threat of an epidemic that could be fatal to the entire population."

Loss of agricultural and livestock biodiversity

Genetic erosion in agricultural and livestock is the loss of biological genetic diversity – including the loss of individual genes, and the loss of particular recombinants of genes (or gene complexes) – such as those manifested in locally adapted landraces of domesticated animals or plants that have become adapted to the natural environment in which they originated.

The major driving forces behind genetic erosion in crops are variety replacement, land clearing, overexploitation of species, population pressure, environmental degradation, overgrazing, governmental policy, and changing agricultural systems. The main factor, however, is the replacement of local varieties of domestic plants and animals by other varieties or species that are non-local. A large number of varieties can also often be dramatically reduced when commercial varieties are introduced into traditional farming systems. Many researchers believe that the main problem related to agro-ecosystem management is the general tendency towards genetic and ecological uniformity imposed by the development of modern agriculture.

Prevention by human intervention, modern science and safeguards

In-Sifu conservation

With advances in modern bioscience, several techniques and safeguards have emerged to check the relentless advance of genetic erosion and the resulting acceleration of endangered species towards eventual extinction. However, many of these techniques and safeguards are too expensive yet to be practical, and so the best way to protect species is to protect their habitat and to let them live in it as naturally as possible.

Wildlife sanctuaries and national parks have been created to preserve entire ecosystems with all the web of species native to the area. Wildlife corridors are created to join fragmented habitats (see Habitat fragmentation) to enable endangered species to travel, meet, and breed with others of their kind. Scientific conservation and modern wildlife management techniques, with the expertise of scientifically trained staff, help manage these protected ecosystems and the wildlife found in them. Wild animals are also translocated and reintroduced to other locations physically when fragmented wildlife habitats are too far and isolated to be able to link together via a wildlife corridor, or when local extinctions have already occurred.

Ex-Sifu conservation

Modern policies of zoo associations and zoos around the world have begun putting dramatically increased emphasis on keeping and breeding wild-sourced species and subspecies of animals in their registered endangered species breeding programs. These specimens are intended to have a chance to be reintroduced and survive back in the wild. The main objectives of zoos today have changed, and greater resources are being invested in breeding species and subspecies for then ultimate purpose of assisting conservation efforts in the wild. Zoos do this by maintaining extremely detailed scientific breeding records (i.e. studbooks) and by loaning their wild animals to other zoos around the country (and often globally) for breeding, to safeguard against inbreeding by attempting to maximize genetic diversity however possible.

Costly (and sometimes controversial) ultra-modern ex-situ conservation techniques have emerged that aim to increase the genetic biodiversity on our planet, as well as the diversity in local gene pools, by guarding against genetic erosion. Modern concepts like seedbanks, sperm banks and tissue banks have become much more commonplace and valuable. Sperm, eggs and embryos can now be frozen and kept in banks, which are sometimes called "Modern Noah's Arks" or "Frozen Zoos". Cryopreservation techniques are used to freeze these living materials and keep them alive in perpetuity by storing them submerged in liquid nitrogen tanks at very low temperatures. Thus, preserved materials can then be used for artificial insemination, in vitro fertilization, embryo transfer and cloning methodologies to protect diversity in the gene pool of critically endangered species.

It is today possible to save an endangered species from extinction by preserving only partsof specimens, such as tissues, sperm, eggs, etc. – even after the death of a critically endangered animal, or collected from one found freshly dead, in captivity or from the wild. A new specimen can then be "resurrected" with the help of cloning, so as to give it another chance to breed its genes into the living population of the respective threatened species. Resurrection of dead critically endangered wildlife specimens with the help of cloning is still being perfected, and is still too expensive to be practical, but with time and further advancements in science and methodology it may well become a routine procedure not to far into the future.

Recently, strategies for finding an integrated approach to in situ and ex situ conservation techniques have been given considerable attention, and progress is being made.

References

1. ^ Stephen J. O'Brien, Chief, Laboratory of Viral Carcinogenesis, National Cancer Institute (April 1992). "GENETIC EROSION A Global Dilemma". National Geographic (Posted online by Oslo Cyclotron Laboratory at the Department of Physics, UiO; The University of Oslo in Norway): 136. Retrieved 20 October 2007. A population bottleneck creates a shrinking gene pool that leaves fewer and fewer mating partners. What are the genetic implications? The animals become part of a high stakes poker game – with a crooked dealer. After beginning with a 52-card deck, the players wind up with, say, five cards that they are dealt over and over. As they begin to inbreed, congenital effects appear, both physical and reproductive. Often abnormal sperm increase; infertility rises; the birthrate falls. Most perilous in the long run, each animal's immune defense system is weakened. Thus, even if an endangered species in a bottleneck can withstand whatever human development may be eating away at its habitat, it still faces the threat of an epidemic that could well be fatal to the entire population.
2. ^ See DIVERSEEDS online discussion forum on the integrated approach.

-Wikipedia 

POPULATION MODEL

A population model is a type of mathematical model that is applied to the study of population dynamics.

Models allow a better understanding of how complex interactions and processes work. Modeling of dynamic interactions in nature can provide a manageable way of understanding how numbers change over time or in relation to each other. Ecological population modeling is concerned with the changes in population size and age distribution within a population as a consequence of interactions of organisms with the physical environment, with individuals of their own species, and with organisms of other species (biophysical env.) The world is full of interactions that range from simple to dynamic. Many, if not all, of Earth’s processes affect human life. The Earth’s processes are greatly stochastic and seem chaotic to the naked eye. However, a plethora of patterns can be noticed and are brought forth by using population modeling as a tool. Population models are used to determine maximum harvest for agriculturists, to understand the dynamics of biological invasions, and have numerous environmental conservation implications. Population models are also used to understand the spread of parasites, viruses, and disease. The realization of our dependence on environmental health has created a need to understand the dynamic interactions of the earth’s flora and fauna. Methods in population modeling have greatly improved our understanding of ecology and the natural world.

History

Late 18th-century biologists began to develop techniques in population modeling in order to understand dynamics of growing and shrinking ball populations of living organisms. Thomas Malthus was one of the first to note that populations grew with a geometric pattern while contemplating the fate of humankind. One of the most basic and milestone models of population growth was the logistic model of population growth formulated by Pierre François Verhulst in 1838. The logistic model takes the shape of a sigmoid curve and describes the growth of a population as exponential, followed by a decrease in growth, and bound by a carrying capacity due to environmental pressures.
Population modeling became of particular interest to biologists in the 20th century as pressure on limited means of sustenance due to increasing human populations in parts of Europe were noticed by biologist like Raymond Pearl. In 1921 Pearl invited physicist Alfred J. Lotka to assist him in his lab. Lotka developed paired differential equations that showed the effect of a parasite on its prey. Mathematician Vito Volterra equated the relationship between two species independent from Lotka. Together, Lotka and Volterra formed the Lotka–Volterra model for competition that applies the logistic equation to two species illustrating competition, predation, and parasitism interactions between species. In 1939 contributions to population modeling were given by Patrick Leslie as he began work in biomathematics. Leslie emphasized the importance of constructing a life table in order to understand the effect that key life history strategies played in the dynamics of whole populations. Matrix algebra was used by Leslie in conjunction with life tables to extend the work of Lotka. Matrix models of populations calculate the growth of a population with life history variables. Later, Robert MacArthur and E. O. Wilson characterized island biogeography. The equilibrium model of island biogeography describes the number of species on an island as an equilibrium of immigration and extinction. The logistic population model, the Lotka–Volterra model of community ecology, life table matrix modeling, the equilibrium model of island biogeography and variations thereof are the basis for ecological population modeling today.

Equations

Logistic growth equation:

Lotka-Volterra equation:

Island biogeography:

Species area:

Examples of individual-based models

Logical deterministic individual-based cellular automata model of an ecosystem with one species. The model demonstrates a mechanism of S-shaped population growth.

Logical deterministic individual-based cellular automata model of interspecific competition for a single limited resource. A mechanism of competitive exclusion of one species by another.

References

1. ^ ^a b Uyenoyama, Marcy; Rama Singh, Ed. (2004). The Evolution of Population Biology. Cambridge University Press. pp. 1–19. Cite uses deprecated parameter |coauthors= (help).
2. ^ Worster, Donald (1994). Nature's Economy. Cambridge University Press. pp. 398–401.
3. ^ ^a b McIntosh, Robert (1985). The Background of Ecology. Cambridge University Press. pp. 171–198.
4. ^ Renshaw, Eric (1991). Modeling Biological Populations in Space and Time. Cambridge University Press. pp. 6–9.
5. ^ Kingsland, Sharon (1995). Modeling Nature: Episodes in the History of Population Ecology. University of Chicago Press. pp. 127–146.
6. ^ Gotelli, Nicholas (2001). A Primer of Ecology. Sinauer.

External Links

• GreenBoxes code sharing network. Greenboxes (Beta) is a repository for open-source population modeling code. Greenboxes allows users an easy way to share their code and to search for others shared code.

- Wikipedia 

SEED DISPERSAL SYNDROME

A seed dispersal syndrome is a mutualistic plant-animal interaction. Seed dispersals syndromes are morphological characters of seeds correlated to particular seed dispersal agents. Dispersal is the event by which individuals move from the site of their parents to establish in a new area. A seed disperser is the vector by which a seed moves from its parent to the resting place where the individual will establish, for instance an animal. Similar to the term syndrome, a diaspore. Is a morphological functional unit of a seed for dispersal purposes.

Characteristics for seed dispersal syndromes are commonly fruit colour, mass, and persistence. These syndrome characteristics are often associated with the fruit that carries the seeds. Fruits are packages for seeds, composed of nutritious tissues to feed animals. However, fruit pulp is not commonly used as a seed dispersal syndrome because pulp nutritional value does not enhance seed dispersal success. Animals interact with these fruits because they are a common food source for them. Although, not all seed dispersal syndromes have fruits because not all seeds are dispersed by animals. Suitable biological and environmental conditions of dispersal syndromes are needed for seed dispersal and invasion success such as temperature and moisture.

Seed dispersal syndromes are parallel to pollination syndromes, which are defined as floral characteristics that attract organisms as pollinators. They are considered parallels because they are both plant-animal interactions, which increase the reproductive success of a plant. However, seed dispersal syndromes are more common in gymnosperms, while pollination syndromes are found in angiosperms. Seeds disperse to increase the reproductive success of the plant. The farther away a seed is from a parent, the better its chances of survival and germination. Therefore, a plant should select certain traits to increase dispersal by a vector (i.e. bird) to increase the reproductive success of the plant.

Evolution

Seeds have evolved traits to reward animals to enhance their dispersal abilities. Differing foraging behaviours of animals can lead to selection of dispersal traits and spatial variation such as increase in seed size for mammal dispersal, which can limit seed production. Seed production is limited by some seed syndromes because of their cost to the plant. Therefore, seed dispersal syndromes will evolve in a plant when the trait benefit outweighs the cost. The seed dispersers themselves play an essential role in syndrome evolution. For example, birds put strong selection pressure on seeds for colour of fruits because of their enhanced vision. Illustrations of such colour evolution include green colour being produced because its photosynthesis abilities are less costly, while red colour emerges as a byproduct for protection from arthropods.

For visible characteristic differences to develop between dispersers and non-dispersers a few conditions need to be met 1. Specialization must increase dispersal success whether morphological, physiological or behavioural 2. Energy investment for dispersal will be taken from energy investment of other traits 3. Dispersal traits will benefit the dispersers over non-dispersers. Phenotypic (visible characteristics) differences in non-dispersers and dispersers can be caused by external factors, kin competition, intraspecific competition and habitat quality.

History

In 1930, Ridley wrote an important book called The dispersal of plants throughout the world, which goes into detail about each form of dispersal; dispersal by wind, water, animals, birds, reptiles and fish, adhesion and people. He details the morphology and traits for each dispersal method, which are later described as seed dispersal syndromes. This began the idea of seed trait selection being associated with a form of seed dispersal. Then in 1969 van der Pijl identified seed dispersal syndromes based on each mechanism of seed dispersal in his book Principles of Dispersal in Higher Plants. He is the pinnacle of seed dispersal syndromes and is cited by many scientists who study seed dispersal syndromes. He describes the morphology of interactions between fruits and flowers and classifies dispersal in invertebrates, fish, reptiles, birds, mammals, ants, wind, water and the plant itself. Janson in 1983 continued the study on seed dispersal syndromes and classified seed dispersal syndromes of fruit by size, colour and husk or no husks in species of Peruvian tropical forest. He went in depth about the interaction between plants that have adapted to seed dispersal by birds and mammals. Willson, Irvine & Walsh in 1989 added more factors to the study of seed dispersal syndromes and looked at differing fleshy fruits and their correlation to moisture and differing ecological factors. They looked at bird-dispersal and mammal-dispersal and how the fruits differed in dispersal syndromes such as colour and size. These scientists began the theory and ideas behind seed dispersal syndromes that are crucial to the evolution of reproduction in plants.

Types and Functions

Dispersal syndromes have been previously classified by: size, colour, weight, protection, flesh type, number of seeds, weight and start time of ripening.,Syndromes are often associated with the type of dispersal and morphology. Also chemical composition can influence the disperser’s fruit choice. The following are types of seed dispersal and their syndromes.

Anemochory

Example of a syndrome of anemochory.

Anemochory is defined as seed dispersal by wind. Common dispersal syndromes of anemochory are wing structures and brown or dull coloured seeds without further rewards. Van der Pijl named seeds for anemochory flyers, rollers, or throwers to represent the seed dispersal syndromes and their behaviour. Flyers are typically categorized as dust diaspores, balloons, plumed or winged. Dust diaspores are small flat structures on seeds that appear to be the transition to wing diaspores, balloons are inflated seed characteristics and plumes are hairs or elongation seed characteristics. Wings have evolved to increase dispersal distance to promote gene flow. Anemochory is commonly found in open habitats, canopy trees, and dry season deciduous forests. Wind dispersers mature in the dry season for optimum high long-distance dispersal to increase success of germination.

Barochory

Barochory is seed dispersal by gravity alone in which a plant's seeds fall beneath the parent plant. These seeds commonly have heavy seed dispersal syndromes. However, heavy seeds may not be a form of seed dispersal syndrome, but a random seed characteristic that has no dispersal purpose. It has been thought that barochory does not develop a seed dispersal syndrome because it does not select for characters to enhance dispersal. It is questionable whether barochory is dispersal at all.

Hydrochory

Hydrochory is seed dispersal by water. Seeds can disperse by rain or ice or be submerged in water. Seeds dispersed by water need to have the ability to float and resist water damage. They often have hairs to assist with enlargement and floating. More features that cause floating are air space, lightweight tissues and corky tissues. Hydrochory syndromes are most common in aquatic plants.

Zoochory

Zoochory is the dispersal of seeds by animals and can be further divided into three classes.

1. Endozoochory is seed dispersal inside animals,
2. Synzoochory is dispersal of diaspores by the mouthparts of animals, and
3. Epizoochory is the accidental dispersal by animals. Differing characteristics of zoochory syndromes include coloured fruits, scented fruits, and different textures for different animals. Endozoochory syndrome characteristics will develop based on palatability of the fruit by an organism. For example, mammals are attracted to scent of a seed and birds are attracted to colour. Endozoochory syndromes have evolved to be ingested by animals and later bypassed in a new environment so the seed can germinate. Synzoochory should possess hard skins to protect seeds from damage of mouthparts; for example, sharp beaks on animals such as birds or turtles. Epizoochory commonly has burrs or spines to transport seeds on the outside of animals. These syndromes are highly associated with animals that have fur, while burrs would be lacking on seeds that are dispersed by reptiles because of their smooth skin. It is believed that not all animals that interact with plant fruits are dispersers because some animals do not increase the successful dispersal of seeds but consume and destroy them. Therefore, some animals are dispersers and some are consumers.

Mammalochory

Mammalochory is specifically the seed dispersal by mammals. The dispersal syndromes for mammalochory include large fleshy fruit, green or dull coloured fruits, and husked or unhusked. The seeds tend to have more protection to prevent mechanical destruction. Mammals rely on smell more than vision for foraging, which causes the seeds they disperse to be more scented compared to bird-dispersed seeds. Animal-dispersed seeds ripen in rainy season when foraging activity is high, resulting in fleshy diaspores. Mammals consume fruits whole or in smaller pieces, which explains the larger seed syndromes. Mammalochory syndromes can increase the reproductive success of the plant compared to seed dispersal syndromes of a plant associated with barochory for example. An example of seed dispersal syndromes associated with mammals that increases reproductive success would be seed-consuming rodents that increase germination by burial of seeds.

Ornithochory

Ornithochory is seed dispersal by birds. Common syndrome characteristics include small fleshy fruits with bright colours and without husks. Ornithochory is common in temperate zones and oceanic islands because of absence of native mammals. Birds have heightened colour vision and swallow seeds and fruits whole, explaining the small and coloured characteristics of dispersal syndromes. Birds have a weak sense of smell, therefore ornithochory syndromes would specialize more in colour than scent, in comparison to mammalochory. Ornithochory can increase the reproductive success of a plant because a bird’s digestive tract increases seed germination after it has been bypassed and dispersed by the bird.

Myrmecochory

Myrmecochory is seed dispersal by ants. Myrmecochory is considered an ant-plant mutualistic relationship. The common syndrome traits for myrmecochory are elaisomes, and are often hard and difficult to damage. Elaisomes are structures that attract ants because they are high in lipid content, providing important nutrients for the ant. Without ants, seed dispersal becomes barochory and dispersal success declines. It is debated if ants are good dispersers and if plants would select for ant dispersal. Ants do clearly interact with seeds, however ants cannot travel very long distances. Therefore, would a plant select for an ant over a bird when birds can disperse seeds much farther than ants, increasing a plant's reproductive success.

Problems in Seed Dispersal Syndromes

Many scientists are skeptical whether seed dispersal syndromes actually exist because their parallel, pollination syndromes, are often disputed in scientific literature. Seed dispersal syndromes do not have much disagreement among scientists. Whether this is due to lack of research or interest in seed dispersal syndromes, or that scientists agree with the idea of seed dispersal syndromes. It also may be that seed dispersal syndromes are harder to test because once seeds disperse they are difficult to collect and study. Jordano (1995) states that the evolution of fruit traits for seed dispersal success is only dependent on diameter. This is one scientist’s perspective but does not appear to be the common consensus among scientists. Colour and olfaction are other common seed dispersal syndromes tested and discussed in scientific literature. One limitation to seed dispersal syndromes mentioned is the limited definitions of syndrome characteristics such as odour or texture. It is possible that there has not been enough research to test these characteristics or they do not play a role in seed dispersal syndromes.

The differences in seed dispersal syndromes appear to be weak, but do exist. There needs to be consideration for the possibility that these syndromes evolved not to benefit seed dispersal but possibility to combat other selective pressures. For example, syndromes may have developed to combat predation or environmental hazards. Predation could produce a secondary metabolite syndrome. Secondary metabolites are compounds that are not used for the primary function of a plant and are normally used as defense mechanisms.

Further Research

Seed dispersal syndromes have not been studied in complete breadth for every seed dispersal method. Therefore, further research should be conducted to fill the gaps of knowledge about dispersal syndromes. The following are problems areas or directions research can continue on the study of seed dispersal syndromes. There is a lack of understanding of morphology in correlation to behavioural traits of dispersers. Research in this area would assist in the understanding of why particular dispersers are selected by plants to enhance reproductive success. Also, understanding movement strategies of factors affecting departure to settlement is important in determining whether seed dispersal syndromes are only affect by plant selection for a disperser. There are few studies concerning phenotype-dependent dispersal and how it affects spatial structures of populations. Distance of dispersal is not researched in enough detail to correlate to a seed dispersal syndrome. More experimental field studies on plant-animal interactions regarding seed dispersal need to be conducted for a thorough understanding of seed dispersal syndromes. There is limited knowledge about the presence of elaisomes and ant behaviour affecting seed dispersal, and how ant-plant interactions evolved under various plant traits. Understanding these interactions would help clarify if myrmecochory did evolve seed dispersal syndromes. Micro and macroevolutionary processes are needed to determine the effects of biological dispersal of seeds. There cannot be inferences about seed dispersal syndromes without robust phylogenies and evolutionary studies. There is also a gap in the understanding of genetic consequences of zoochory. Using genetics could help clarify if these syndromes were formed at random or if they correspond to evolution of seed dispersal. It is unclear if these seed dispersal syndromes evolved for specialization between plants and animals to increase seed dispersal success or if these syndromes are simply formed from generalist plant-animal interactions. Understanding these relationships would clarify the confusion about seed dispersal syndromes and if they are true examples of evolution increasing plant reproductive success or if they have developed without selective pressures.

References

1. ^ Herrera, C. M. & Pellmyr, O. (2002). Plant Animal Interactions: An Evolutionary Approach. USA: Blackwell Science Ltd
2. ^ ^{a b c d e f g} Clobert, J., Le Galliard, J.F., Cote, J., Meylan, S. & Massot, M. (2009). Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations. Ecology Letters, 12, 197-209.
3. ^ ^{a b c d e f} Griz, L.M.S. & Machado, I.C.S. (2001). Fruiting phenology and seed dispersal syndromes in caatinga, a tropical dry forest in the northeast of Brazil. Journal of Tropical Ecology, 17, 303-321.
4. ^ ^{a b c d e} Link, A. & Stevenson, P.R. (2004). Fruit dispersal syndromes in animal disseminated plants at Tinigua National Park, Colombia. Revista Chilena de Historia Natural, 77, 319-334.
5. ^ ^{a b c d e} Tamboia, T., Cipollini, M.L. & Levey, D.J. (1996). An Evaluation of Vertebrates Seed Dispersal Syndromes in Four Species of Black Nightshade. Oecologia, 107(4), 522-532.
6. ^ ^a b c d Herrera, C. M. & Pellmyr, O. (2002).Plant Animal Interactions: An Evolutionary Approach. USA: Blackwell Science Ltd
7. ^ Booth, D. T. (1990). Plant diaspore functions. Journal of Seed Technology, 14(1), 61-73.
8. ^ Fenster, C. B., Armbruster, W. S., Wilson, P., Dudash, M. R. & Thomson, J. D. (2004). Pollination Syndromes and Floral Specialization. Annual Reviews of Ecology, Evolution and Systematics, 35, 375-403.
9. ^ ^{a b c d e f g h i} Castro, S., Ferrero, V., Loureiro, J., Espadaler, X., Silveira, P. & Navarro, L. (2010). Dispersal mechanisms of the narrow endemic Polygala vayredae: dispersal syndromes and spatio-temporal variations in ant dispersal assemblages. Plant Ecology, 207, 359-372.
10. ^ ^{a b c d e f g} Fischer, K.E. & Chapman, C.A. (1993). Frugivores and Fruit Syndromes: Differences in Patterns at the Genus and Species Level. Oikos, 66(3), 472-482.

- wikipedia