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Ecology

Without animals the forest will die

The disappearance of the animals that disperse seeds endanger the survival of the remainder of the Mata Atlântica (Atlantic Rain Forest)

In place of the hubbub of the interaction between the living beings of the forest, there is a threat of a stage without actors. Researchers have proved that hunting and the intensive exploitation of the fruits on which the animals feed themselves, is causing the Brazilian forests to move closer and closer to disappearing. In Amazon, the Brazil Nut trees get older with a reduced chance of renewing themselves because of the intense exploitation of the Brazil Nut tree (Bertholletia excelsa) threatens the survival of the agouti (Dasyprocta spp), the main disperser of the nuts. Already in the remnants of the Mata Atlântica (Atlantic Rain Forest) in the interior of the State of São Paulo, the threat looms on dozens of species of trees which depend on the agouti for dispersing their seeds and promoting the regeneration of stretches of forest.

To evaluate the extension of the danger in these stretches, the biologist Dr. Mauro Galetti, of the Institute of Biosciences of the São Paulo University (Unesp), in Rio Claro, studied the interference of the fragmentation of the forest in the dispersion of seeds and is setting up a data bank about the interactions of fruit-eating animals with the species of vegetation.Dr. Galetti, whose goal is to assist the management projects, evaluates the theme from a global perspective. “The tropical forests are today the last frontier in terms of knowledge, especially in what is referred to as biodiversity.

They are considered to be the largest sources of natural products and are also responsible for the maintenance of essential resources to man, such as water, and for keeping global temperature. Nevertheless, the high levels of deforestation and the conversion of primitive habitats by man, has caused the accentuated decline of both animal and vegetation species. The worst aspect of the extinction few people notice – the loss of the interactions between the animals and the plants, which are responsible for the maintenance of the forests.”

The scattered fragments in the interior of the country are composed of a semi deciduous forest, where many species lose their leaves during the dry season, called the Mata Atlântica (Atlantic Rain Forest). “It is the most threatened Brazilian forest which may totally disappear and it will be necessary to have planned management in all of the fragments that remain. If not, many stretches of forest are going to disappear in less than 100 years.”, alerts Dr. Galetti. The SOS Mata Atlântica (Atlantic Rain Forest) Foundation confirmed that of the 8.9 million hectares of the original area of the semi deciduous forest of the State, there remains only 189,000 hectares or 2.06%.

Jatobá, monkey and tapir
Among the studies of the project, Dr. Galetti singled out the dispersion of the seeds of the jatobá tree (Hymenaea courbaril) by the agouti. In the same way as other species of the leguminous family and some palm trees, the jatobá tree has very large seeds, more than 2.5 centimeters in diameter. Plants with large seeds, which no bird can swallow are the most threatened in the patches of forest. They are dispersed exclusively by tapirs (Tapirus terrestris) and agouti. Since the tapirs are widely hunted to the point of local extinction, the agouti inherits the title of the only dispersers of these large seeds in the patches of forest.

Just like the squirrel, the tapir eats some of the seeds and buries the rest so as to have food for another season. When it changes territory, forgets some seeds or is killed by felines, the abandoned seed germinates and gives origin to a new plant. Dr. Galetti reveals that the agouti is also the target of hunters in parts of the forest in the country of São Paulo State, which threatens the survival of the jatobá and of other 50 species of trees with large fruit, which have in the animal their only disperser, among them are various species of palm trees such as the Syagrus oleracea and Astrocaryum aculeatissimum.

The researcher said that the black-capped capuchin monkey (Cebus apella) and the Muriqui monkey (Brachyteles arachnoides) eats the pulp of the fruit of the jatobá tree and throw away the large and hard seeds, that afterwards are eaten or buried far away by the agouti. Even if a seed germinates at the foot of the jatobá, the young plant would not be able to compete with the adult for light and nutrients. As matter of fact, the closer they are to the mother plant, the greater is the possibility the seed being eaten by other rodents and wild boar, attracted by the quantity of fruit under the tree. “Without the dispersion by the agouti, we will only have living fossils. For example, when a jatobá of 150 years of age dies, there will not be another around to substitute it. This could modify greatly the dynamics of the forest with a domino effect, bringing about unbalances in all of the food chain.”

Strategies and birds
Another curious interaction occurs between the mistletoe, the shrub of the genre Phoradendron that is a parasite of the Tabebuia spp and the tanagers, birds of the genre Euphonia that are the only seed dispersers of this plant. The tanager eats the fruit of the mistletoe and the seeds arrive on the trunk of the Tabebuia spp, through the feces of the bird. Covered with birdlime, the seeds stick to the trunk, where they germinate rapidly. “It is a very delicate relationship of interdependence and we are studying how it can be broken with the environmental disturbances.”, said Dr. Galetti.

The survival strategy of the Ormosia arborea, a tree of the leguminous family, depends on an extremely rare type of event, discovered by Dr. Galetti after three years of observations using automatic cameras. The red and black seed of this species, used in necklaces and bracelets, looks like a succulent fruit that consequently attracts the birds. It is a parasite system, because the plant does not offer anything to the bird, however despite the low level of dispersion, the trick works, when the bird realizes the mistake it has already been swallowed or spit out, then the seed on the ground can germinate.

Imitating this strategy, Dr. Galetti and the students Eliana Cazeta and Cecília Costa made artificial fruit with modeling clay in order to verify alterations in the behavior of birds that eat the fruit of shrubs. They distributed white red and black artificial fruit, the colors of the fruit that the birds eat, on the edges and deep in the stretches of forest. They chose the band of the semi-thicket because in it, with less tall trees, close to 85% of the plants are dispersed by birds or bats and only 15% by a mechanism of the plant itself, such as explosion, which throws the seeds far away. In the band of high trees such as the jequitibá (Cariniana legalis), with 30 to 40 meters in height, the animals only disperse the seeds of half of the species, the other half is dispersed by the effect of the wind or by the plant itself.

“The results”, related Dr. Galetti ” showed that the taller forests had more fruit pecked and removed than the shorter ones, indicating a probable diminution of dispersion of seeds by birds in the small patches. Moreover, black fruit are less pecked by the birds in the deep of the forest than at the edge, while for the red fruit there was no difference between the edge and the middle. This experiment showed, for the first time, that the fragmentation of a forest affects the possibility of a fruit being dispersed by a bird, depending on the color of the fruit and where the plant is located in the environment. For this reason, it is expected that smaller patches of forest possess more shrubs with black fruit on the edge than forests that haven’t greatly altered. Nobody imagined that the forest fragmentation could affect differently the species of the semi-thicket depending on the color of the fruit”.

The fringe effect
This simple experiment pointed to an important risk factor for the regeneration of fragmented forests, the fringe effect. Dr. Galetti explained that when the forest is fragmented, its fringes receive much more wind and sunshine than the core, which diminishes considerably humidity among other impacts. This facilitates the invasion of exotic species not native to the forest. For example, grass does not occur inside a preserved forest, where it does not have any means way to compete for the light. The grass which invades the fringe, however, stalls the regeneration of forest in that location. The cycle goes on, the more light on the fringe, less humidity, greater invasion of grass or of other exotic species. This process of strangulation of the original forest could lead to many fragmented pieces of forest and its disappearance in less than 100 years.

The more or less aggressive attack of the fringe affect on a piece of forest depends on many variables, which require a study in the specific management of each area. “In forest fragments that have plantations of eucalyptus skirting them, there is less fringe effect than in those surrounded by sugar-cane or pasture. This is because the eucalyptuses break the action of the wind, which could knock down lots of trees on the fringe. As there is no regeneration on the edge due to the grass, the forest goes on diminishing more and more.” The quantity of environmental variables found was a little frustrating for the team.

“We had been looking for a pattern on the effects of fragmentation in the dispersion of seeds for the semi-deciduous forests of São Paulo, in the search for the solutions to these problems. Although there are some clear patterns as in the case of the jatobá, the variables of each fragment f forest are so many, that each area responded in its own manner. Each patch of forest has its unique history of disturbance, type of surrounding such as coffee, sugar cane or eucalyptus, pressure of hunting and other difficulties.”

Continuous management
Summing up, if there are no animals to carry out for free the dispersion of seeds in order to recompose the forest and maintain it self-sufficient, it will be necessary to replant species and also to reintroduce the animals. Dr. Galetti adds that the fragments of forest need to be managed continually: introducing into the environment disperser animals such as the agouti and to control hunting ,for example, could make the animal population increase more than need be and cause another impact in the food chain. “Once a disturbance has taken place in the forest, it is difficult to remake mother nature.”

In Brazil there are few people qualified to adequately manage the fragment of forest. “There are not any university courses that prepare what in the United States are called wildlife managers, dedicated to the managing of the wildlife. Who ends up doing the managing is a biologist or the forest engineer. All the units of conservation should have a group of researchers dedicated to the local managing. Without adequate management, we will be losing our biodiversity more and more. This shows a huge field of work for biologists in this area, much more than in biotechnology.”

Comparing his study with that of the Dynamic Biology Project of Fragmented Forests (PDBFF), in operation since 1979 in the North region of the country by the National Research Institute of the Amazon (INPA) and the Smithsonian Institution of the United States, Dr. Galetti points to a difference. The PDBFF removed parts of the forest and left symmetrical blocks of 1, 10, 100 or 1.000 hectares isolated from the continuous forest, while in São Paulo the fragmentation is much more chaotic and much older, with fragments of forest that have been isolated for 100 or 150 years. “Firstly, the coffee wave knocked down almost all of the forest, mainly because access was very easy in a flat region. An then the cycles of sugar cane and eucalyptus came. An isolated fragment of forest in a sea of sugar-cane has no chance to receive seeds and loses its diversity over the time.”

The project looked at patches stands of forest, four with close to 300 hectares and four above 1,000 hectares (see insert). In the Cerrado – a type of a wooded Savannah, another ecosystem that, like the Mata Atlântica, is recorded on the list of the 25 areas of richest and most threatened biodiversity on the planet according to the preservationist organization Conservation International, the biologist considers the situation less serious as to the reproduction of species than in the semi deciduous forest.

“Many plants of the Cerrado have vegetative reproduction and do not depend only on fruit. If they are cut down, they re-sprout or throw out a long root and generate another individual further on, while in the forest the majority of the trees that are cut don’t re-sprout”. Dr. Galetti comments that the dispersion of seeds is a very new line of research in the country. He, who took his doctorate at the University of Cambridge in England, on a study of the dispersion of the seeds of the palm tree (Euterpe edulis) in the Mata Atlântica, also studied in Indonesia the dispersion done by bears and hornbills (birds of various species and genres similar to toucans). On his return, he obtained from FAPESP the incentive to begin in 1997 this present project, which should be concluded in July. In 1998 he began teaching in the Department of Ecology of the São Paulo State in Rio Claro(Unesp), and set up the Phenology Group and Seed Dispersion Group along with professor Patricia Morellato of the Botany Department.

Apart from Dr. Galetti’s group, few within the State of São Paulo dedicate themselves to this area. Dr. Wesley Rodrigues Silva, of the Institute of Biology of the University of Campinas, and Dr. Jean Paul Metzger, of the Institute of Biosciences of the University of São Paulo (IB-USP), are coordinating projects in the Biota-FAPESP Program. Also in IB-USP, Dr. José Carlos Motta Jr. has meetings with researchers dedicated to the question. To attract more interest in the area, Dr. Galetti and Dr. Wesley Silva organized the Third International Symposium of Fruit and Seed Dispersion between the 6th and the 11th of August past in São Pedro (a tourist center in the State of São Paulo) and which had more than 300 participants from 30 countries. There, Dr. Galetti’s group presented 15 studies and the award for the best poster was given for the work of two researchers from IB -USP on the dispersion of the Brazil Nut of Para by the agouti.

Agouti and Brazil Nuts
The work was carried out on the indigenous lands of the Caiapó Indians in the south west of the State of Pará, as part of the Pinkaiti Project. Dr. Claúdia Baider worked on the demography and dispersion of the seeds as her doctorate thesis, while Maria Luisa da Silva Pinto Jorge took her master degree studying the life, daily activity and population density of the agouti. Orientated by Dr. Carlos Augusto da Silva Peres of IB-USP, they carried out their research in one of the few remaining Brazil Nut tree locations still unexplored in the Amazon, about two hours by boat from the village of A’Ukre, close to the town of Redenção.

The forest of the Brazil Nut tree which was studied is open, with boscages of palms, bamboos and lianas. There is a dry season of five months and for half of it not a drop of water falls. Cláudia states that the major part of the Brazil Nut trees are in conglomerates, which could have resulted from the pattern of dispersion of the agouti. The agouti eats the nuts but buries some seeds which end up germinating. It takes away the fruit in all directions and can cover large distances, but distributes the majority of the seeds relatively close to the trees.

The fruit, which weighs between 800 grams and 1.5 kilograms, is made of wooden shell covered by another shell of bark. It is extremely hard and the agouti takes between 40 and 50 minutes to gnaw a hole in it until it reaches the nuts. The Brazil Nut tree is important for the extraction economy of the Amazon, but its uncontrolled extraction is threatening the survival of the agouti and of the Brazil Nut tree itself.

The bits of forest
These were the eight forest fragments of the Mata Atlântica (Atlantic rain forest) studied in the interior of the State of São Paulo by Dr. Galetti and his team:

– The State Park named Morro do Diabo (Devil´s Hill), in Teodoro Sampaio. It is the largest of the forest stands with 35,000 hectares and preserves its complete fauna, including wildcats.

– The Ecological Station of Caetetus, in Gália close to Bauru. It has nearly 2,100 hectares and almost unaltered fauna, expect for agouti and wildcats.

– The Barreiro Rico Ranch in Anhembi, Piracicaba. There are close to 1,800 hectares, there is a lot of game, but density of agouti is low and there are no tapir.

– The Mosquito Ranch in Pontal do Paranapanema, near to Presidente Prudente, with close to 2,000 hectares. It has its entire fauna preserved.

– The São José (Saint Joseph) Forest in Rio Claro. There are 230 hectares, without any agouti or tapir, with only a few examples of black-capped capuchin monkey (Cebus apella) and the buffy-tufted-ear marmoset (Callithrix aurita) .

– The Santa Genebra (Saint Geneva) Forest. A Municipal Reserve of Campinas with 250 hectares. There are no agouti or tapir, only the black-capped capuchin monkey and the howling monkey (Aloutta fusca).

– The Ribeirão Cachoeira Forest in Campinas, with close to 230 hectares. It only has howling monkeys.

– The Igurê Ranch in Galia. Close to 320 hectares, without agouti or tapir, but with disperser birds such as toucans (Ramphastidae family) and bell-birds (Procnias nudicolis).

The fruit and their seed spreaders
Color, size and other characteristics of fruit are important on order to be identified by the dispersers of seeds. Dr. Galetti revealed that fruit dispersed by birds are generally red or black and sweet tasting such as the pau-de-viola tree (Citharexyllum mirianthum) and the Brazil cherry (Eugenia spp), or fatty such as the nutmegs (Virola spp). Those dispersed by mammals are almost always sweet, yellow, pungent and pithy, such as the guava (Campomanesia spp) and the bakupari (Rheedia gardneriana).

Those that are dispersed by bats are green, with a strong smell and of easy capture in flight. Examples are: the fig (Ficus spp) and the tropical almond tree (Terminalia cattapa). There are even those adapted to dispersion by ants, such as the castor bean (Riccinus communis) and the capixingui (Croton floribundus), which have a small oily reward for the insects. There are also fruit that do not require animals for the dispersion of their seeds. They use the wind for this as they are endowed with wings or feathers, such as the araribá (Centrolobium tomentosum), the red bramble palm tree (Cariniana legalis) and the cedar(Cedrella fissilis).

The Projects
1. Fruit and Fruit Dispersion in Semi Deciduous Forests: Structure of the Community and the Impact in the Dispersion of Seeds in Forest Fragments in the State of São Paulo (nº 96/10464-7); Modality
Program of Support to Young Researchers; Coordinator Dr. Mauro Rodrigues Galetti – Institute of Biosciences of Unesp in Rio Claro;
Investment R$ 104,087.00
2. Demography and the Ecology of the Dispersion of Seeds of Bertholletia excelsa HBK (Lecythidaceae) in Wild Brazil Nut trees groves in the East Amazon (nº 95/03054-4); Modality Aid to Research Project; Coordinator Dr. Carlos Eduardo da Silva Peres – USP; Investment R$ 72,138.19

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