The threat to rainforests in tropical Latin America (Achard

The complex
ecosystems found within tropical rainforests provide habitats for two thirds of
all plant and animal species found on Earth (Bierregaard et al., 1992; Gardner et al.,
2009). As a result, rainforests contain an unprecedented richness in
biodiversity (Heywood, 1995; Laurance, 2007). Rainforests harbour valuable
economic resources and supply a wide variety of ecosystem services including
carbon storage, air quality improvement and hydrological services (Chomitz and
Kumari, 1998; Parrotta et al., 2012).

Consequently, these impacts benefit humans on a local, regional and global
scale (Costanza et al., 1997; Kremen et al., 2000).

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Deforestation is
an ever-increasing threat to rainforests in tropical Latin America (Achard et al., 2002; Höbinger et al., 2012). As a result of human
influence, rainforests are being exploited due to an increased demand for its
natural resources (Cuaron, 2000). Other destructive human activities include
clearing forests for agricultural purposes and timber production, resulting in habitat
loss, fragmentation and a reduction in biodiversity (Steffan-Dewenter et al., 2007; Shaver et al., 2015). The way a species
responds to the effects of habitat disturbance can vary significantly across
taxonomic groups, geological regions, and ecological metrics (Cuaron, 2000; Gibson
et al., 2011). For instance, it has
been discovered that areas at risk of deforestation inhabit globally threatened
bird species that are restricted to old-growth primary rainforests (Balmford
and Long, 1994; Turner and Corlett, 1996), and will not cross large open
clearings (Stork et al., 2009).

 

Despite the
increased rate of deforestation, some studies have documented forest recovery
as a result of secondary regrowth (Wright 2005; Aide et al., 2013). This occurs when converted land is exhausted,
abandoned and allowed to regrow (Dunn, 2004). Secondary forests are important
due to their potential to recover degraded land, support a wide variety of species,
and act as biological corridors (Brown and Lugo, 1990; Algeet-Abarquero et al.,
2015). However, relatively little is known about how successful secondary
forests are in providing refuge for specialist species that are dependent on
old-growth primary rainforests (Stokstad, 2008; Chazdon et al., 2009).

 

Costa Rica is located
in Central America and is considered to be one of the most biologically diverse
regions in the world due to it geographical position and geological history (González-Maya et
al., 2016). It is
estimated that approximately 500,000 species (5% of all living species)
inhabits this small Mesoamerican country, despite only covering 0.01% of the
Earth’s landmass (Sanchez-Azofeifa et al.,
2002). The Osa Peninsula has been estimated to inhabit 4000-5000 vascular
plant, 8000 insect, 124 mammal, 71 reptile, 46 amphibian and 375 bird species,
of which 18 are endemic to the region (Sanchez-Azofeifa et al., 2002). Thus, making it an important area to study the
effects of habitat loss and fragmentation.

 

During the last
three decades, several authors have conducted research to document regional
deforestation and habitat fragmentation across Costa Rica (Sader and Joyce,
1988; Sanchez-Azofeifa et al., 2001).

Habitat fragmentation is a prominent issue across the Osa Peninsula, resulting
in forest reserves becoming increasingly more isolated and reducing the number
of biological corridors available for species (Broadbent et al., 2012). For instance, a previous study conducted by
Sanchez-Azofeifa (2002) found that the proportion of forest cover in the Osa
Peninsula declined from 97% in 1979 to 89% by 1997, with the total forest area
declining from 977 km2 in 1979 to 896 km2 by 1997. These
findings suggest that the conservation management strategies implemented in
this area are not adequate for preventing habitat destruction. Furthermore,
there is an clear lack of biodiversity research that address some of the
primary challenges facing conservation (Balmford et al., 2005), such as understanding optimal reserve design and
location, species persistence in converted or modified forest habitats, and the
future sustainability of rainforest conservation practices (Gardener et al., 2008). The majority of studies
focus on the conservation value of reserves, whilst the conservation value of
areas outside of reserves is poorly understood (Lindenmayer and Franklin,
2002).

 

Estimating forest
cover, fragmentation, and measuring biodiversity is vital in understanding how
anthropogenic influences affect ecological processes, in turn providing a basis
for effective conservation planning (Brooks and Helgen, 2010; Sanchez-Azofeifa et al., 2001). Furthermore, it is
important to measure how the abundance and distribution of a species varies in
the edges compared to the interiors of rainforest habitats to understand how
fragmentation affects populations. The loss a single species or population can
lead to major irreversible effects on ecosystem functioning and services
(Ceballos and Ehrlich, 2002).

 

The degree of
rainforest degradation can be divided into three categories; primary,
secondary, and degraded (Gibson et al.,
2011). Primary rainforests are largely comprised of old-growth forests, characterised
by pristine continuous vegetation, with little or no sign of human disturbance (Gibson
et al., 2011). Secondary forests develop
when exhausted land is abandoned and allowed to regrow (Nepstad et al., 1991). Consequently, the trees
that make up secondary forests are less developed and therefore smaller, with a
less complex canopy structure than that of primary rainforest (Brown and Lugo,
1990). Degraded habitats are those that have been subject to large-scale
anthropogenic disturbance and have undergone extensive modification to other
forest types, such as selectively logged forests and agricultural land (Gibson et al., 2011). Using primary, secondary,
and degraded rainforest to represent the gradual decline in rainforest quality,
it can be determined how biodiversity is affected by human disturbance and
habitat loss, with amphibians, birds and reptiles used as focal taxa. The
results will enable effective conservation management strategies to be
implemented, therefore ensuring the survival of tropical rainforest species. Thus,
serving as a model for other countries.

 

This study aims
to determine if anthropogenic disturbance in rainforest habitats affects the
biodiversity of amphibians, birds and reptiles, compared between primary,
secondary and degraded rainforest types. The study hypothesized that the biodiversity
of amphibians, birds and reptiles would be lower in the more disturbed
habitats, with degraded rainforest being the lowest, followed by secondary
rainforest, and then primary rainforest.

 

 

 

 

 

 

The transformation and degradation of tropical rainforests
are the leading cause of reduction in biodiversity worldwide (Sanchez-Azofeifa et al., 2001). This results in
significant habitat loss, which is considered to be the primary driving force
behind modern day extinctions (Dent and Wright, 2009). Rainforests inhabit the
majority of all described species, and an even larger proportion of undescribed
species (Raven, 1988; Dirzo and Raven, 2003). Therefore, the continuous
degradation and loss of tropical rainforests could lead to a globally mass
extinction (Dent and Wright, 2009).

 

Disturbed and secondary forests will be critical if these
countries are to conserve their biodiversity. The luxury of concentrating
conservation efforts solely on old-growth forests is no longer a viable
conservation strategy in many tropical countries, and it is essential that we
have a better understanding of the potential of secondary and degraded forests
to help conserve tropical forest species (Dent
and Wright, 2009).