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Abstract

Summary Tropical rain forest fragmentation is one of the most pervasive threats to the conservation of biological diversity, affecting different levels of biological organization including populations, communities and ecosystems. Forest fragmentation involves the creation of "habitat edges" and consequently the so called "edge effects" that generally have a negative impact on the biotic and physical environment. The spatial attributes of fragments in the landscape include fragment size, shape, isolation and the matrix type surrounding the fragments. Although these spatial attributes influence the prevalence and magnitude of the edge effects, they can constitute important threats to biodiversity by themselves. The increment of fragment isolation in highly fragmented landscapes can negatively affect inter-fragment dispersal movements of both plant and animal species, modifying important ecological processes such as pollination and seed dispersal. In this sense, actions to increase the population size and the persistence of several plant and animal species include the establishment of biological corridors. Biological corridors increase landscape connectivity, and may reduce extinction rates by increasing inter-fragment movements and favoring the access to resources available in more than one forest fragment.
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To cite this chapter: Benítez-Malvido J, Arroyo-Rodríguez V. 2008. Habitat fragmentation, edge effects and biological corridors in
tropical ecosystems. In: Encyclopedia of Life Support Systems (EOLSS). Del Claro K, Oliveira PS, Rico-Gray V, Ramirez A,
Almeida AA, Bonet A, Scarano FR, Consoli FL, Morales FJ, Naoki J, Costello JA, Sampaio MV, Quesada M, Morris MR,
Palacios M, Ramirez N, Marcal O, Ferraz RH, Marquis RJ, Parentoni R, Rodriguez SC, Luttge U (editors). International
Commision on Tropical Biology and Natural Resources. UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net]
[Retrieved August 29, 2008]
HABITAT FRAGMENTATION, EDGE EFFECTS AND BIOLOGICAL
CORRIDORS IN TROPICAL ECOSYSTEMS
Julieta Benítez-Malvido and Victor Arroyo-Rodríguez
Centro de Investigaciones en Ecosistemas, Universidad Nacional Autonoma de Mexico, Antigua Carretera a Patzcuaro
No. 8701, Ex−Hacienda de San Jose de la Huerta, Morelia, Michoacan, Mexico
Summary
Tropical rain forest fragmentation is one of the most pervasive threats to the conservation
of biological diversity, affecting different levels of biological organization including
populations, communities and ecosystems. Forest fragmentation involves the creation of
"habitat edges" and consequently the so called "edge effects" that generally have a negative
impact on the biotic and physical environment. The spatial attributes of fragments in the
landscape include fragment size, shape, isolation and the matrix type surrounding the
fragments. Although these spatial attributes influence the prevalence and magnitude of the
edge effects, they can constitute important threats to biodiversity by themselves. The
increment of fragment isolation in highly fragmented landscapes can negatively affect
inter-fragment dispersal movements of both plant and animal species, modifying important
ecological processes such as pollination and seed dispersal. In this sense, actions to increase
the population size and the persistence of several plant and animal species include the
establishment of biological corridors. Biological corridors increase landscape connectivity,
and may reduce extinction rates by increasing inter-fragment movements and favoring the
access to resources available in more than one forest fragment.
Keywords: Biodiversity loss, connectivity, extinction, fragment size, habitat loss, isolation, tropical
rain forest.
1. Introduction
Deforestation and forest fragmentation have become the most important threats for the
maintenance of biodiversity. Tropical rain forests are one of the most affected ecosystems
with annual rates of deforestation between 100 000 and 150 000 km2. Tropical forests are
also one of the most biodiverse ecosystems of the planet as they contain between 50% and
80% of all the terrestrial species, and they have a critical role on the maintenance of the
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planet homeostasis. Therefore, their destruction may not only threaten the maintenance of
biodiversity, but could also affect climatic and hydrological cycles at local, regional and
global scales. In addition to the loss of forest cover, the process of fragmentation results in
a change on the spatial pattern of the remaining forest (e.g., increase in number of forest
fragments, decrease in fragment size, and increase in fragment isolation), leading to the loss
of ecosystem continuity. These spatial changes produce a wide range of effects across
several levels of biological organization, affecting biological populations and communities,
as well as ecological processes that may modify the overall functioning of the ecosystem.
The magnitude of the effects that tropical rain forest fragmentation has on the biota
and physical environment depend on different elements or aspects that characterize the
fragmented landscapes including: total amount of forest cover, number of forest fragments,
fragment size, shape and isolation, and the characteristics of the matrix (i.e., modified
native vegetation such as deforested areas, cattle pasture, agricultural crops, urban areas,
etc.) that surrounds the fragments. These same elements would also determine the
magnitude of the so called "edge effects", which are an inevitable consequence of forest
fragmentation and imply the influence of processes originated in the matrix that surrounds
the fragments. In this chapter we describe the consequences that tropical rain forest
fragmentation has across different levels of biological organization including populations,
communities and ecosystems, as well as on the physical environment of the remaining
forest. Thereafter, we describe the influence of edge effects and fragment attributes (i.e.,
size, shape, isolation and surrounding matrix) on the biota and physical environment.
Finally, we pointed out the importance and inconveniences of the so called biological
corridors, present in some fragmented landscapes and relevant for the maintenance of the
remaining plant and animal populations within the fragments. For each section, the
examples given on fragmentation effects come from studies conducted in different tropical
forests around the world.
2. Habitat Fragmentation
Habitat may be broadly defined as the range of environments suitable for a given species.
That is, it is a species-specific concept. Therefore, to simplify the present synthesis, we
equated "habitat" with "native tropical rain forest", as this vegetation type is very important
for a large number of animal and plant species. Thus, we define habitat fragmentation as a
landscape-scale process in which the continuous habitat is reduced into smaller habitat
remnants. This implies the loss of habitat and its sub-division into a variable number of
remaining fragments scattered within a matrix of modified habitat. In addition to the
changes on habitat pattern described above, the primary effect of fragmentation is the
alteration of the microclimate within and around the fragment. These environmental
changes have major implications on several plant and animal species; modify biotic
interactions and the functioning of the ecosystems. While some changes on the habitat are
visible immediately after fragmentation (e.g., shifts in habitat pattern, changes in
population sizes, forest structure and composition at edges) others may appear in the long
term (e.g., genetic related changes on populations, extinction of species with slow life
cycles).
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The effects of habitat fragmentation on the tropical biota are very variable and
depend on several factors, such as: (1) taxon characteristics (e.g., population size, habitat
and diet requirements, dispersal capacity, etc.); (2) the spatial scale of the analysis; (3) the
ecological processes under study; (4) habitat type; and (5) landscape characteristics (e.g.,
topography, soil type, etc.). Furthermore, there are factors that are not easily detected and
therefore are difficult to evaluate, such as: (1) the response time of populations to
fragmentation (e.g., denominated "extinction debt"); (2) the biogeographical position of the
species under study; and (3) synergisms between different processes (e.g., fragmentation
and hunting; fragmentation and climatic change).
2.1. Impact of Habitat Fragmentation on Populations
Fragmentation involves the decline of many plant and animal populations, altering birth,
mortality and growth parameters, conducting in some cases to the local and/or regional
extinction of particular species. The extinction proneness of a species in a fragmented
habitat is related to factors such as habitat or niche specialization, home range size,
mobility and dispersal capacity, extent of geographic distribution, population density or
rarity, edge sensitivity, body size, trophic level, age-sex class and dietary specialization.
For example, species with restricted geographic distributions and/or reduced population
density are more sensitive to extinction, as these species are the most vulnerable to
stochastic (i.e., unpredictable) threatening processes such as environmental (e.g.,
fluctuations in climate, natural catastrophes), demographic (e.g., year-to-year variability in
reproductive success) and genetic (e.g., genetic drift) stochasticity. In contrast, species with
larger populations are less sensitive to stochastic threatening processes, and therefore, they
have a higher probability to persist in the long term.
In addition to the stochastic threatening processes, populations are confronted with
several deterministic (i.e., predictably lead to population declines) threats; which can be
classified as exogenous (originating independently of the species’ biology) or endogenous
(originating as part of the species’ biology). For example, habitat loss, habitat degradation,
anthropogenic pressures (e.g., logging and poaching), sub-division and habitat isolation are
all exogenous threatening processes that can affect a declining population inhabiting
fragmented landscapes; while disruptions to dispersal, changes in social systems and
physiological stress, and loss of genetic diversity are endogenous threatening processes that
can accelerate population decline in fragmented habitats. Continuing with the factors
described above, species with larger home range size and/or high dietary specialization will
be more vulnerable to exogenous threats such as habitat loss and degradation; while species
with low dispersal capacity through the matrix will be more vulnerable to the sub-division
and isolation of the habitat.
Therefore, fragmentation effects on the population of particular species cannot be
generalized, as each species responds individualistically to a range of processes related to
its requirements for food, shelter, space, suitable climatic conditions and to interspecific
processes (e.g., competition, predation and mutualisms). Although the majority of the
species are directly or indirectly affected by fragmentation, plant and animal species in the
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tropics present three types of responses to the fragmentation of their habitat: (1) a positive
response (e.g., increased population size of pioneer plant species, some invertebrates and
some rodents in fragments compared with continuous forested areas); a negative response
(e.g., decline in population size of many primates species, loss of genetic diversity in
howler monkeys of Belize, death of large trees in Brazil, and local extinction of some dung
and carrion beetles in Brazil); and (3) a neutral response (no effects) (e.g., the population
size of some plant species in 1 000 m2 of continuous forest did not differ from 1 000 m2 of
a fragmented landscape of Los Tuxtlas, Mexico).
2.2. Fragmentation Effects on Communities
The effects of fragmentation on tropical plant and animal communities include changes in
species diversity, composition, abundance, distribution and biotic interactions. Probably the
most important is the loss of biological diversity. However, as forest fragments are prone to
be colonized or invaded by exotic plant and animal species and diseases, in some tropical
forests some taxa (e.g., some frogs, small rodents, and secondary plant species) have shown
an increment in species richness after fragmentation; whereas, in some others, there are not
differences in species richness after fragmentation (e.g., richness of some arthropods was
similar in large and small fragments in a study in south-eastern Australia). Disruptions to
species interactions have particularly severe consequences when keystone species are
involved as these species play an important role in maintaining ecosystem function and
structure. For example, some predators (e.g., jaguar, puma, ocelot) are important regulators
of the density of many herbivore populations, and their disappearance may favor the
overexploitation of the vegetation by herbivores that increase their population sizes due to
the lack of predators. Similarly, some tree species (e.g., the genus Ficus) are important food
sources for many species of birds and mammals and their disappearance or altered
phenology may affect numerous species of animals.
In fragmented tropical communities changes in biotic interactions affect
competition, predation, parasitism and mutualisms (e.g., seed dispersal and pollination).
Nearly 90% of tropical tree species are dispersed by animals. Therefore, plant species
depending on animals for the dispersal of their seeds may be strongly affected in a
fragmented community. The extinction of animal seed dispersers may reduce the
distribution areas and population size of several plant species, or may reduce the possibility
of colonizing new habitats. These effects increase population isolation eventually leading
them to extinction. In Uganda, tree species dispersed by chimpanzees failed to recruit into
forest fragments where this primate species was lacking. In isolated land-bridge islands in
Lago Guri, Venezuela, several islands have populations of howler monkeys at densities up
to more than 30 times greater than those on the mainland, and researchers have
demonstrated that these "hyperabundant" herbivorous have a strong positive influence on
aboveground plant productivity (by increasing the transference of nutrients through their
feces), with a positive, indirect effect on bird species richness.
The plant-pollinator interaction is sensitive to any kind of disturbance. In small and
isolated fragments pollen flux is reduced, affecting fruit and seed set with harmful
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consequences to the quality and quantity of the progeny. Fragmentation affects several
types of pollinators with strong effects in the reproductive success on plant populations and
on the genetic structure of remnant populations. Pollination in fragmented habitats includes
a reduction in the abundance of pollen vectors as consequence of changes in the
environment and in the availability of resources, reduced frequency of visits as the
distribution of floral resources changes, and by competitive exclusion of floral resources by
exotic pollinators. For example, various tropical tree species have shown reduced fruit and
seed set in fragmented habitats (e.g., Samaena saman, Dinizia excelsa, Shorea siamensis,
Clatasetum viridiflavum) due to reduced pollination and increased isolation.
2.3. Fragmentation Effects on Ecosystems
Most research on habitat fragmentation has been focused on plant and animal populations
and communities, and rarely on ecosystem processes. The principal climatic changes
produced by forest fragmentation affecting ecosystem functioning and that are particular
harmful at forest edges and small fragments (< 10 ha) include radiation fluxes, wind
incidence, fire frequency and changes in the hydrological cycle (e.g., evapotranspiration). It
has been suggested that not just species richness, but functional diversity is important to
maintain nutrient and energy fluxes in the ecosystems. Solar radiation, carbon dioxide,
temperature, water and soil nutrients are important for the primary productivity of tropical
rain forests and are strongly modified by habitat fragmentation. The magnitude of such
impacts depends on the size of the fragment as well as on its orientation, slope and matrix
type.
Energy balance within a fragmented forest differs from that of a continuous forest,
especially when the original natural vegetation was denser than that developing after
fragmentation. Vegetation structure is modified in a fragmented habitat altering wind
fluxes, reducing humidity and increasing desiccation. In tropical forests the incidence of
warm and dry winds in fragmented areas increases tree mortality and the incidence of fires.
Strong winds reduce the substrate available for microorganisms and the resources coming
from the soil. The removal of the natural vegetation changes the rates of water interception,
water loss and evapotranspiration altering the hydrological cycle and may also increase soil
erosion.
The kind of matrix (see below) that surrounds the fragment, for example, affects
radiation balance due to increase isolation on the fragment surface. For disturbed forests, in
general, diurnal temperatures are higher and nocturnal temperatures are lower than the ones
present in the unperturbed forest. In Manaus, Brazil, temperatures were around 3 ºC higher
in fragments than in the continuous forest. The alteration on temperature regimes could
affect nutrient cycling as well as the biology of several plants (e.g., seed germination) and
animals (e.g., egg hatching in some insect species) as well as biotic interactions such as
competition, predation and parasitism (e.g., fungal infection on leaves). Furthermore,
fragments may accumulate pollutants and nutrients that are transported by the wind from
urban and agricultural areas, at their edges, affecting nutrient cycling and microbial
activity.
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3. Edge Effects
Forest fragmentation implies the creation of "habitat edges" and consequently the so called
"edge effects". The edge effect could be defined as the interaction of two adjacent
ecosystems separated through an abrupt transition. Forest fragmentation increases the
amount of edges in the landscape producing important physical (e.g., radiation, moisture,
temperature, wind speed, and soil nutrients) and biological (e.g., species composition,
competition, predation, etc.) changes along and close to the edge. Fragment edges are the
most altered area of a fragment and the penetration depth of the edge effects vary widely
from tens of meters (e.g., soil moisture in Manaus, Brazil) to several kilometers (e.g.,
recruitment failure of trees in Borneo). Forest edges may control the flux of organisms
between forest and non-forest habitats. Edges are also the point of entry of external
influences such as fire and the invasion of exotic species including pathogens to the
remaining forest.
The survival and persistence of several animal and plant species, and their
interactions (e.g., herbivory, pathogen infection on plants, nest predation, ant-plant
interactions, etc.) are affected close to the fragment edge. Therefore, ecological processes
close and along forest edges differ from those at forest interior. Naturally, edge effects vary
widely between species, and contrasting edge responses have been found between species
with different life history strategies and habitat requirements. Studies in plant ecology have
found that pioneer species (light demanding) have a speedy growth near forest edges, while
old-growth species (shade tolerant) can establish and growth only under the closed canopy
in the forest interior. Not all edges are necessarily detrimental for all native species,
especially when edges are gradual or of low structural contrast (e.g., developed secondary
forests).
4. Influence of the Spatial Attributes of the Fragments
Here, we grouped fragmentation effects under four categories that together describe the
spatial attributes of individual fragments in fragmented landscapes, and influence the
incidence and magnitude of the edge effects: (1) fragment size; (2) fragment shape; (3)
fragment isolation; and (4) matrix type.
4.1. Fragment Size
Fragment size is considered the most important spatial attribute that affects the maintenance
of biodiversity in a fragmented landscape. Small fragment area imposes a maximum limit
on population size that leaves species vulnerable to local extinction. For many plant and
animal species (e.g., old-growth tree species and large predators or carnivores) habitat
conditions are ideal in large areas of unmodified tropical rain forest vegetation. As
fragmentation increases, the size of the remaining fragments decreases. Smaller fragments
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may have lower number of species than larger ones, for example because resources in
smaller fragments may be more limited. Larger fragments may present larger populations
of different taxonomical groups and larger populations persist for longer time. Furthermore,
larger fragments may have higher colonization to extinction ratio, are more likely to contain
undisturbed areas which are required by some species, are more likely to hold a range of
environmental conditions which constitute adequate habitats for different sets of species,
and are more likely to capture species with patchy distributions. Small fragments may also
be more easily affected by anthropogenic disturbances such as hunting, logging, fires and
cattle grazing. However, in some situations smaller fragments may be more easily
colonized or invaded by exotic species increasing species diversity as small fragments
present greater proportion of edge. Small fragments (< 10 ha in area) may also provide the
last refuge for many native plants and animals for some ecosystems, as in the Atlantic
forest of Brazil.
4.2. Fragment Shape
The negative effects of fragment shape are decreased in large fragments as larger fragments
present a greater proportion of forest interior relatively free of edge effects. The proportion
of a forest fragment affected by edge effects depends on the relation between fragment size
and shape; being the smallest and most irregularly shaped fragments the ones with a greater
area affected by edge effects. The survival and persistence of several animal (e.g., beetles,
birds) and plant species (e.g., all life stages of tree species) and their interactions (e.g.,
herbivory, pathogen infection on plants, nest predation, ant-plant interactions, etc.) are
affected close to the fragment edge. The magnitude of such effects depends on the species
attributes, species habitat requirements and matrix type. However, in some cases large
irregular fragments may have a positive effect on the populations (e.g., howler monkeys),
for example, some large irregular fragment along rivers or living fences (fencerows) may
function as dispersal corridors or "stepping stones". In these large fragments, shape
complexity may have a positive effect on population persistence, as they can be colonized
more frequently than are compact fragments. Increased colonization of complex fragments
occurs because fragments with high shape complexity (e.g., ameba shape) have a
proportionally greater amount of edge, increasing the likelihood that a fragment will be
encountered by a moving individual. In Los Tuxtlas, Mexico, the local people maintain
native vegetation along streams and delimit their properties with living fences (i.e., trees).
These management practices produce more irregularly shaped fragments but reduce
considerably their isolation facilitating the movement of animals (i.e., primates) between
them. Nevertheless, the opposite trend has been observed for some animal species, as shape
complexity can also facilitate emigration. Thus, the combination of increased emigration
and colonization may lead to greater variability in the population size of the most complex
shaped fragments.
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4.3. Fragment Isolation
Fragmentation increases the isolation of the remaining habitat fragments. Isolation can
negatively affect day-to-day movements (e.g., between foraging resources) of a given
species, and dispersal of plants (e.g., seeds) and animals (e.g., juveniles and sub-adults).
The distance among the remaining forest fragments and the continuous forested area is also
important for the maintenance of biodiversity because the dispersal capacity of several
plant and animal species may be affected by increasing isolation. Some species could be
negatively affected by distances of less than 100 m between forest fragments, or between
forest fragments and continuous forest, as they are incapable of crossing cleared areas (e.g.,
some birds, euglossine bees, beetles, frogs, etc.). However, the negative effects of distance
may vary depending on the trait considered (e.g., population size, species richness, genetic
diversity), the taxa (e.g., births and bats may be less affected than arboreal mammals) and
habitat configuration. The negative effects of isolation may be reduced when there are
several small fragments between large fragments, as small fragments may act as "stepping
stones" for several species; or when two forested areas or fragments are connected by the so
called biological corridors that are formed by the remaining vegetation. Furthermore, some
matrix types disrupt dispersal more than others, as particular species can use some matrix
types for their mobility than others. For example, some plant species dispersed by gravity
(e.g., the palm Astrocaryum mexicanum in Los Tuxtlas, Mexico), could be drastically
affected by fragment isolation; whereas some others like those dispersed by animals and
wind are less affected.
In some cases, isolated populations may utilize the resources of more than one patch
for foraging, shelter, reproduction, etc. (a process named "landscape supplementation").
The ability or capacity of a species to utilize more than one patch may favor its persistence
in fragmented landscapes where resources may be scarce and of low quality. Other effect
related to fragment isolation is the so called "rescue effect" that occurs when a given
population is declining within a fragment and receives immigrant individuals from a
neighboring fragment "rescuing" the population that is in the verge of extinction.
4.4. Matrix Type
Matrix type (e.g., cattle pastures, secondary forest, urban and agricultural areas, mining,
etc.) and the related physical factors determine the magnitude of fragmentation effects on
the biota and the physical environment. The type of matrix affects the dispersal of plants
and animals; may provide food and space for the species capable to survive in it, and may
determine the magnitude of edge effects within the fragment. For example, in the Central
Amazon if a forest fragment is surrounded by a secondary vegetation dominated by large
and dense Cecropia trees, edge effects on the vegetation are less detrimental than when
surrounded by a secondary vegetation dominated by the more slender and sparse Vismia
trees. Furthermore, a number of studies have demonstrated that generalist species - which
can use also resources from the matrix - maintained higher populations in fragmented
landscapes than specialist species that depended on resources available only in fragments.
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The structure and composition of the matrix ("effective isolation") can resist, hinder
or enhance movement behavior, affecting colonization/extinction dynamics within the
fragments, and population size. Therefore, fragment isolation does not solely depend on the
Euclidian distance between fragments but on the matrix type surrounding them. The matrix
may also provide suitable habitat for some native species, especially if it is structurally
similar to the native vegetation within the fragments, enhancing food availability and
habitat connectivity for these species. For example, in Mexican coffee plantations ants were
actively foraging in the surrounding matrix and some species were even able to survive in
the matrix habitat in perpetuity. Similarly, in some fragmented landscapes of Africa, some
mammals species that inhabit forest fragments, can take some resources from the matrix.
5. Biological Corridors
Biological corridors refer to linear elements or strips of vegetation (but not necessarily of
native vegetation) in the landscape, connecting two or more habitat patches that have been
linked in historic time and that function as passageway for the biota. Thus, biological
corridors increase connectivity between different elements of a landscape. Connectivity
determines the connectedness between fragments of suitable habitat (commonly equated to
native vegetation), as well as the connectedness of ecological processes (e.g., biotic and
abiotic interactions, hydrological flows) across multiple scales. Therefore, as previously
discussed for the opposite process (i.e., fragment isolation), lack of connectivity may be a
major threat for wildlife, and the establishment and maintenance of landscape
linkages/connectivity of native vegetation networks or wildlife corridors, is a common
conservation strategy.
Biological corridors are aimed to increase the exchange/movement of individuals
between forest fragments, promote new foraging areas for many animals, act as refuges for
several plant and animal species, act as wind barriers diminishing edge effects, and can stop
the desiccation of rivers and streams (e.g., riparian corridors). However, biological
corridors may not be used by all native species, not all ecological processes are effectively
facilitated though biological corridors (e.g., disturbance processes), and depending on their
shape they are prone to edge effects. Furthermore, they facilitate the spread of introduced
species and diseases, and increase the vulnerability to catastrophic events. Nevertheless,
biological corridors are usually more likely to have beneficial effects on native species and
ecological processes than detrimental effects favoring, on the whole, the persistence of the
species at local and regional scales.
The inclusion of biological corridors in reserve design has become an important
conservation tactic for protecting biodiversity. The Mesoamerican Biological Corridor
(MBC), for example, is a region-wide initiative covering 768 990 km2 and comprises
southern Mexico, Guatemala, Belize, El Salvador, Honduras, Nicaragua, Costa Rica and
Panama. Although the region contains only 0.5 % of the world’s land surface, it contains
around 7 % of the planet’s biological diversity. Mesoamerica does not only include about
22 eco-regions (e.g., lowland rainforest, grasslands, semi-arid woodlands, pine savannas,
etc.) but is also considered to be one of the world’s most important centers of the origin of
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agriculture. The MBC is intended to conserve biological and ecosystem diversity in a
manner that promotes sustainable social and economic development in the region.
6. Conclusions
Forest edges and fragments are becoming dominant features in many tropical landscapes
threatening native populations and communities and the functioning of tropical rain forest
ecosystems. The magnitude of fragmentation effects on the different levels of biological
organization depends on a complex interplay of factors related to fragment spatial
attributes. On the whole, despite of the fact that each species responds individualistically to
fragmentation, forest fragmentation is detrimental for the maintenance of biodiversity
because tropical forest species need functional ecosystems to survive. Fortunately,
conservation actions, such as the implementation of biological corridors at a landscape and
regional scales, are being undertaken to lessen fragmentation effects on tropical
ecosystems.
Acknowledgments: The authors thank the Biological Dynamics of Forest Fragments Project, in Manaus,
Brazil; the Los Tuxtlas Biosphere Reserve, Veracuz, Mexico; the Montes Azules Biosphere Reserve, Chiapas,
Mexico; and to their people, for providing the opportunity to gain knowledge and expertise on the fascinating
and challenging topic of tropical rain forest fragmentation.
Glossary
Habitat: The range of environments suitable for a particular species.
Habitat loss: Loss of habitat for a particular species.
Habitat fragmentation: The breaking apart of sub-division of continuous habitat for a particular species.
Landscape: Following Fischer and Lindenmayer (2007), a human-defined area ranging in size from ca. 3 km2
to ca. 300 km2.
Matrix: In modified landscapes usually not native vegetation (e.g., deforested areas, cattle pasture,
agricultural crops, urban areas, etc.) that surrounds the forest fragments of native vegetation.
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Biographical Sketches
- Julieta Benitez-Malvido received the Bachelors degree in Biology (cum laude) from Universidad Autonoma Metropolitana-
Iztapalapa, in Mexico City in 1988; the Master in Science degree in Ecology from Durham University, at the United Kingdom; and
the PhD. from Cambridge University, United Kingdom in 1994. She is a principal researcher in the Center for Ecosystem Research,
National Autonomous University of Mexico (UNAM, 1996-present); assistant professor in Population Ecology and Conservation;
and Research Associate, to the Biological Dynamics of Forest Fragments Project, National Institute for Research in the Amazon
(INPA)-Smithsonian Institution (1991-present) and at the Long Term Ecosystem Research (LTER), international program at the
Chamela site (Mexico). Current research sites include the Brazilian Amazon and several locations at tropical Mexico (Los Tuxtlas,
Chajul, Cozumel and Chamela). Research interests: tropical ecology; tropical forest recovery after human disturbances (e.g.,
fragmentation, deforestation and impact of roads); biotic interactions of plants with herbivores and pathogens in disturbed tropical
habitats, and tropical forest restoration.
- Victor Arroyo-Rodriguez received the B.Sc. (biology) degree from Universidad Autonoma de Madrid, Spain, in 2002, and both the
M.Sc. and Ph.D. degrees from Instituto de Ecologia A.C., Mexico, in 2005 and 2007, respectively. Nowadays he is a postdoctoral
fellow at the Centro de Investigaciones en Ecosistemas (Universidad Nacional Autonoma de Mexico). His main research interest is
conservation biology in human-modified tropical rain forests. He has published ca. 20 papers in wildlife ecology, forest ecology and
biodiversity conservation in fragmented landscapes, and has scientific presentations in numerous national and international
congresses and symposia.
... The mobility of the species from one region to another depends on various environmental factors, including climate conditions, habitat fragmentation, species competition, etc. [10,11]. It has a massive impact on the ecosystem. ...
... One of the major concerns is the fragmentation of the ecological habitats, which was considered an invasive threat to biodiversity. Habitat fragmentation can define as a landscape-scale process in which the continuous habitat is reduced into more minor habitat remnants [10]. The size, shape, edge of the habitat fragments, and habitat isolation are some significant factors having huge implications on the species interaction and species survival [7,11]. ...
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Spatio-temporal pattern formation over the square and rectangular domain has received significant attention from researchers. A wide range of stationary and non-stationary patterns produced by two interacting populations is abundant in the literature. Fragmented habitats are widespread in reality due to the irregularity of the landscape. This work considers a prey-predator model capable of producing a wide range of stationary and time-varying patterns over a complex habitat. The complex habitat is assumed to have consisted of two rectangular patches connected through a corridor. Our main aim is to explain how the shape and size of the fragmented habitat regulate the spatio-temporal pattern formation at the initial time. The analytical conditions are derived to ensure the existence of a stationary pattern and illustrate the role of the most unstable eigenmodes in determining the number of patches for the stationary pattern. Exhaustive numerical simulations help to explain the effect of the spatial domain size and shape on the transient patterns and the duration of the transients.
... Recently, a pantropical meta-analysis of biodiversity metrics in disturbed versus undisturbed areas showed that primate diversity, species richness, and abundance are negatively affected by agriculture and logging (de Almeida-Rocha et al. 2017). Habitat change directly affects primates by limiting ranging patterns, access to resources, dispersal, and gene flow and increasing intra-and interspecific competition and disease transmission (Chapman et al. 2005;Benítez-Malvido & Arroyo-Rodríguez 2008). On top of large-scale habitat change, primates in anthropogenically modified areas often have higher rates of hunting than those in relatively undisturbed areas (Peres 2001). ...
... Our results showed there was an overall significant positive effect of habitat loss on GC levels across the studies examined. Primates living in small fragments tend to have limited ranges, restrained access to resources, and reduced genetic diversity (Benítez-Malvido & Arroyo-Rodríguez 2008). Because many disturbances are directly correlated to habitat loss (e.g., hunting, logging, and human habitat encroachment [Arroyo-Rodríguez et al. 2013]), the impact on primates can be multidimensional. ...
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As humanity continues to alter the environment extensively, comprehending the effect of anthropogenic disturbances on the health, survival, and fitness of wildlife is a crucial question of conservation biology. Many primate populations occupy sub-optimal habitats prone to diverse anthropogenic disturbances that may be sources of acute and chronic stress. Quantification of glucocorticoid concentrations has repeatedly been used to explore the impact of disturbances on physiological stress. Although it is still debated, prolonged elevation of glucocorticoid levels might impair reproduction, growth, and immune system activity of individuals. In this study, we quantified the effect of anthropogenic disturbances on physiological stress in primates using a global meta-analysis based on data from 26 articles, spanning 24 distinct species in 13 different countries. Anthropogenic disturbances were classified into six distinct categories: habitat loss, habitat degradation, ongoing logging, hunting, tourism, and other human activities. We calculated effect sizes (Hedges' g) using the standardized mean difference in glucocorticoid concentrations between primates affected by human activity and their undisturbed conspecifics. We ran random-effects models and subgroup analyses to estimate the overall effect as well as a cumulative effect size for each disturbance category. Overall, primates inhabiting sites subject to anthropogenic disturbances exhibited significantly higher glucocorticoid levels (g = 0.60; 95% CI = 0.28 to 0.93). Habitat loss and hunting were overall associated with increased glucocorticoid concentrations, while the cumulative effects of the other disturbances were not statistically significant. Biologically, higher glucocorticoid levels may increase fitness by enabling individuals to overcome the challenges linked to anthropogenic disturbances. On the other hand, primates in disturbed environments may suffer from sustained elevated glucocorticoid levels. In order to strengthen future research, it is necessary to systematically control for confounding factors (e.g. diet, reproductive status, predatory pressure, resource availability) and better understand the link between glucocorticoid levels and the health, fitness, and survival of animals. Article impact statement: Anthropogenic disturbances induce physiological stress responses in free-ranging primates, as revealed by increased glucocorticoid levels. This article is protected by copyright. All rights reserved.
... Anthropic effects may affect natural vegetation causing disturbances in their climatic and structural characteristics and, consequently, modify the conditions for the occurrence of fauna (Benítez-Malvido & Arroyo-Rodríguez, 2008;Laurence et al., 2013). Fragmentation of forest environments, for example, can expose forest edge areas to conditions of higher insolation, higher temperature, and lower unit (Murcia, 1995;Lima-Ribeiro, 2008;Arruda & Eisenlohr, 2016), which affects the occurrence of many animal populations (Benítez-Malvido & Arroyo-Rodríguez, 2008). ...
... Anthropic effects may affect natural vegetation causing disturbances in their climatic and structural characteristics and, consequently, modify the conditions for the occurrence of fauna (Benítez-Malvido & Arroyo-Rodríguez, 2008;Laurence et al., 2013). Fragmentation of forest environments, for example, can expose forest edge areas to conditions of higher insolation, higher temperature, and lower unit (Murcia, 1995;Lima-Ribeiro, 2008;Arruda & Eisenlohr, 2016), which affects the occurrence of many animal populations (Benítez-Malvido & Arroyo-Rodríguez, 2008). In this context, some insect groups may be susceptible to anthropogenic changes on the edges of natural vegetation and are often used as habitat modification bioindicators (Brown, 1997). ...
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Caatinga is a very important and neglected dry tropical forest biome of Brazil. Recent evidence indicates that anthropogenic threats to Caatinga have grown in recent years, and there are still gaps in the knowledge of how these effects alter biodiversity. In the present study, we evaluated the effects of vegetation structure and edge proximity on the distribution of bioindicator insects (galling insects and ants) in an arboreal Caatinga area under the influence of a monoculture in Brazil. We recorded a total of 10 species and 2,131 specimens of ants and 11 species and 29 individuals of galling insects. Species richness, abundance, and composition of galling insects and ants did not differ between edge and interior plots of the forest. Ant diversity was also not affected by the structural parameters of vegetation (plant abundance, vegetation cover, and vegetation height). On the other hand, the plant abundance positively influenced the richness and the abundance of galling insects in the plots. Our findings suggest that the distribution of ants and galling insects in Caatinga forest edge and interior environments did not differs likely due the opening of the canopy gives the arboreal Caatinga relatively homogeneous climatic characteristics throughout the forest. Already the structure of vegetation positively influences galling insects due to the high degree of dependence that endophagous life-form generates on these insects. Our results show that despite similar responses to the edge effect, ants and galling insects respond differently to vegetation structure, indicating that the structuring of these insect communities is guild-dependent.
... Approximately half the pine-oak forest and tropical dry forest (TDF) fragments measure around 21 ha and < 3 ha, respectively . The condition of the TDF is alarming, since fragments below 10 ha have limited ecological functionality, mainly leading to biodiversity loss (Benitez-Malvido & Arroyo, 2008). However, data are limited and there are no studies on the faunal diversity within these remnants. ...
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La Montaña, one of seven regions making up the state of Guerrero, Mexico, has high social-ecological vulnerability. Its extreme poverty and marginalization levels are among the country’s highest, superimposed in a context of severe ecosystem degradation. We evaluated the social-ecological resilience of two indigenous communities of this region engaged in agroecological projects by integrating the Resilience Assessment and MESMIS methodological proposals, using qualitative and quantitative indicators. The most critical aspects were the low quality of forest fragments, crop losses through hurricanes, lack of access to information, low socioeconomic infrastructure and lack of gender equity. On the other hand, formal and informal social organization is a major strength. Crop losses due to drought or pests are not significant, but a more critical situation is foreseen in the face of climate change. Local efforts drive the main strategies to maintain a minimum level of resilience but will not be sufficient if unaccompanied by structural changes.
... Landscape connectivity is defined as the degree to which the landscape facilitates or inhibits movement between source patches (Taylor, Fahrig, Henein, & Merriam, 1993). Connectivity is considered as a key issue for preserving biodiversity and maintaining the stability and integrity of natural ecosystems (Alohou et al., 2017;Benitez-Malvido & Arroyo-Rodríguez, 2008;Bogaert et al., 2011;Damschen et al., 2019;Damschen, Haddad, Orrock, Tewksbury, & Levey, 2006). ...
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Forests are the leading ecosystems that are under threat due to the pressure of global change. Being under pressure for a forest ecosystem means fragmented and isolated habitats, decrease in biodiversity and change in the landscape. In recent years, restoring landscape connectivity by minimising landscape fragmentation has been recognised as a key strategy to conserve biodiversity. Well-connected habitat networks are thought to both protect existing populations and help adaptation under climate change. It is therefore priority to understand how best to maintain and develop connectivity in fragmented landscapes at multiple spatial scales for effective conservation of forest biodiversity. In this study, fragmentation analysis was performed using area, edge, and isolation metrics in the forest matrix in the Rize landscape and connectivity corridors were interpreted to manage the impact of this fragmentation on species and habitats. The fragmentation analysis was carried out on 3 classes as broad-leaved, coniferous, and mixed using land cover/land use data with the years 1990-2018. The connectivity corridors between these classes were analysed using core area data and resistance maps. According to the results; it was observed that fragmentation in broad-leaved and coniferous classes and an increase in mixed forest class. In the connectivity analysis it was observed that the limiting effects arising from human activities increased more in 2018 compared to 1990. The results of this study showed that in a fragmented forest matrix, connectivity corridors can be identified and reconstructed the conditions necessary for the survival of biodiversity
... This means a fragmentation of forests and habitats due to disruption of landscape connectivity and contiguity, provoking the dispersal of animals, and creating new edges that expose forests to exploitation and further degradation (Benítez-Malvido & Arroyo-Rodríguez, 2008;Saunders et al., 1991). A total of 13 hydropower projects fall within 10 km of the buffer zone of the Rupi-Bhaba Wildlife Sanctuary (WLS). ...
Article
Fragile ecosystems of the Himalayas have seen rampant land-use changes in recent times due to proliferation of hydropower development promoted as a climate change mitigation strategy for global energy transition. Further, in order to mitigate the loss of forest lands diverted for hydropower projects, countries like India have compensatory afforestation policies, which have meant more physical interference in natural landscapes, whose long-term consequences remain under-researched. This study conducted between 2012 and 2016 uses information from government data and ground research to examine the extent, nature and impact of forest diversion for hydropower projects in the remote, ecologically vulnerable Kinnaur Division of Himachal Pradesh in the Western Himalayas. It also studies the implementation of ‘compensatory afforestation’ undertaken as a ‘mitigation’ strategy as part of this forest diversion process. The study found that not only have construction activities for hydropower projects impacted existing land-use, disturbed forest biodiversity and fragmented the forest landscape, but the related compensatory afforestation plantations are also ridden with problems. These include abysmally low presence of surviving saplings (upto 10%) interspecies conflict, infringement on local land usage, and damage by wildfires and landslides. The study critically examines the role of state led institutions and global green growth policies in driving and legitimizing these developments in the name of ‘mitigation’, ultimately causing more harm to fragile local ecosystems and communities dependent on these.
... species composition, competition, predation, etc.) changes along and close to the edge. The proportion of forest fragment affected by edge effects depends on the relation between fragment size and shape; the smallest and most irregularly shaped fragments are those with a greater area affected by edge effects 4 . ...
... In particular, the effect of habitat's boundaries on the invasive species spread remains poorly understood, especially in case of a nontrivial landscape geometry. Meanwhile, in a somewhat more general ecological context, the importance of the boundaries and the habitats shape for the population dynamics is widely recognized ( Benitez-Malvido and Arroyo-Rodriguez, 2008 ). In our recent work, we addressed the above problem by considering invasive spread in a dumbbell-shaped domain where two large habitats are connected by a narrow passage or corridor and showed that the effect of the corridor can be nontrivial and counterintuitive ( Alharbi and Petrovskii, 2018 ). ...
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Coastal forested wetlands support many endemic species, sequester substantial carbon stocks, and have been reduced in extent due to historic drainage and agricultural expansion. Many of these unique coastal ecosystems have been drained, while those that remain are now threatened by saltwater intrusion and sea level rise in hydrologically modified coastal landscapes. Several recent studies have documented rapid and accelerating losses of coastal forested wetlands in small areas of the Atlantic and Gulf coasts of North America, but the full extent of loss across North America’s Coastal Plain (NACP) has not been quantified. We used classified satellite imagery to document a net loss of ~ 13,682 km2 (8%) of forested coastal wetlands across the NACP between 1996 and 2016. Most forests transitioned to scrub-shrub (53%) and marsh habitats (24%). Even within protected areas, we measured substantial rates of wetland deforestation and significant fragmentation of forested wetland habitats. Variation in the rate of sea level rise, the number of tropical storm landings, and the average elevation of coastal watersheds explained about 78% of the variation in coastal wetland deforestation extent along the South Atlantic and Gulf Coasts. The rate of coastal forest loss within the NACP (684 km2/y) exceeds the recent estimate of global losses of coastal mangroves (210 km2/y). At the current rate of deforestation, in the absence of widespread protection or restoration efforts, coastal forested wetlands may not persist into the next century.
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Research on fragmented ecosystems has focused mostly on the biogeograpbic consequences of the creation of habitat “islands” of different sizes and has provided little of practical value to managers. However, ecosystem fragmentation causes large changes in the physical environment as well as biogeograpbic changes. Fragmentation generally results in a landscape that consists of remnant areas of native vegetation surrounded by a matrix of agricultural or other developed land. As a result fluxes of radiation, momentum (La, wind), water, and nutrients across the landscape are altered significantly. These in turn can have important influences on biota within remnant areas, especially at or near the edge between the remnant and the surrounding matrix. The isolation of remnant areas by clearing also has important consequences for the biota. These consequences vary with the time since isolation distance from other remnants, and degree of connectivity with other remnants. The influences of physical and biogeographic changes are modified by the size, shape, and position in the landscape of individual remnant, with larger remnants being less adversely affected by the fragmentation process. The Dynamics of remnant areas are predominantly driven by factors arising in the surrounding landscape. Management of, and research on, fragmented ecosystems should be directed at understanding and controlling these external influences as much as at the biota of the remnants themselves. There is a strong need to develop an integrated approach to landscape management that places conservation reserves in the context of the overall landscape
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We reviewed empirical data and hypotheses derived from demographic, optimal foraging, life-history, community, and biogeographic theory for predicting the sensitivity of species to habitat fragmentation. We found 12 traits or trait groups that have been suggested as predictors of species sensitivity: population size; population fluctuation and storage effect; dispersal power; reproductive potential; annual survival; sociality; body size; trophic position; ecological specialisation, microhabitat and matrix use; disturbance and competition sensitive traits; rarity; and biogeographic position. For each trait we discuss the theoretical justification for its sensitivity to fragmentation and empirical evidence for and against the suitability of the trait as a predictor of fragmentation sensitivity. Where relevant, we also discuss experimental design problems for testing the underlying hypotheses. There is good empirical support for 6 of the 12 traits as sensitivity predictors: population size; population fluctuation and storage effects; traits associated with competitive ability and disturbance sensitivity in plants; microhabitat specialisation and matrix use; rarity in the form of low abundance within a habitat; and relative biogeographic position. Few clear patterns emerge for the remaining traits from empirical studies if examined in isolation. Consequently, interactions of species traits and environmental conditions must be considered if we want to be able to predict species sensitivity to fragmentation. We develop a classification of fragmentation sensitivity based on specific trait combinations and discuss the implications of the results for ecological theory.
His main research interest is conservation biology in human-modified tropical rain forests. He has published ca
  • Victor Arroyo-Rodriguez Received The
  • B Sc Ecologia
  • A C Mexico
Victor Arroyo-Rodriguez received the B.Sc. (biology) degree from Universidad Autonoma de Madrid, Spain, in 2002, and both the M.Sc. and Ph.D. degrees from Instituto de Ecologia A.C., Mexico, in 2005 and 2007, respectively. Nowadays he is a postdoctoral fellow at the Centro de Investigaciones en Ecosistemas (Universidad Nacional Autonoma de Mexico). His main research interest is conservation biology in human-modified tropical rain forests. He has published ca. 20 papers in wildlife ecology, forest ecology and biodiversity conservation in fragmented landscapes, and has scientific presentations in numerous national and international congresses and symposia.
This paper introduces a conceptual framework for understanding the effects of landscape modification on species and communities, discusses how species and communities are affected by landscape modification, and provides management recommendations for biodiversity conservation
  • J Fischer
  • D B Lindenmayer
Fischer J., Lindenmayer D.B. (2007). Landscape modification and habitat fragmentation: a synthesis. Global Ecology and Biogeography 16, 265-280. [This paper introduces a conceptual framework for understanding the effects of landscape modification on species and communities, discusses how species and communities are affected by landscape modification, and provides management recommendations for biodiversity conservation].
finding from the Biological Dynamics of Forest Fragments Project, the world's largest and longest-running experimental study of habitat fragmentation
  • W F Laurance
  • T E Lovejoy
  • H L Vasconcelos
  • E M Bruna
  • R K Didham
  • P C Stouffer
  • C Gascon
  • R O Bierregaard
  • S G Laurance
  • E Sampaio
Laurance W.F., Lovejoy T.E., Vasconcelos H.L., Bruna E.M., Didham R.K., Stouffer P.C., Gascon C., Bierregaard R.O., Laurance S.G., Sampaio E. (2002). Ecosystem decay of Amazonian forest fragments: a 22-year investigation. Conservation Biology 16, 605-618. [This paper synthesizes key finding from the Biological Dynamics of Forest Fragments Project, the world's largest and longest-running experimental study of habitat fragmentation, which has been carried out in Brazil].