Fauna Diversity in Tropical Rainforest: Threats from Land-Use Change Fauna Diversity in Tropical Rainforest: Threats from Land-Use Change

Tropical rainforests are the cradle of life (perfect conditions for life) on Earth, i.e., rich in plant species composition (>250 plant species/hectare) and fauna diversity (>50% of animal species in the world). Rainforests occur near the Earth's equator and cover 6% of the Earth's surface across the tropical regions and are characterized by wet climate, i.e., heavy rainfall (125 — 660 cm), relative humidity (77 — 88%) and temperature (20 — 34°C). They are dominated by a wide range of broad-leaved trees that form dense canopy and the most complex ecosystem. Currently, the tropical rainforest ecosystem is changing faster than ever in human history due to anthropogenic activities, such as habitat loss and degradation due to deforestation for timber and conversion into agri- culture fields (oil palm plantation), mining, fire, climate change, etc. The habitat loss and degradation had adversely influenced the distribution and richness of the fauna species. The current information on the fauna diversity of tropical rainforest is not sufficient and in the future, more research is required to document the various community parameters of the fauna species in order to conserve and protect them. For better future, conservation, and management, we must identify the major drivers of changes and how these factors alter the tropical rainforest.


Introduction
Tropical rainforest usually occurs 10°north and south of the equator, where climate conditions are unique such as humid, warm, and wet. The monthly mean temperature is 18°C and the annual rainfall is not less than 168 cm. Tropical rainforest occurs in four main regions; Central and South America, Central and West Africa, Indo-Malaya and Australia [1]. They are storehouses of a range of food resources for a wide variety of fauna species as well as for human beings, raw material for buildings, and medicines [2,3] and affect the climate [4,5].

Ecological importance of tropical rainforest
Tropical rainforests are the most diverse in the vegetation structure and composition (Figure 1) that supported a diversity of fauna species such as birds, reptiles, mammals, amphibians, and invertebrates, which directly or indirectly depend on them for their survival and existence. They are rich in habitat diversity and provide a variety of resources for the avian species, such as food, habitat, and shelter [6]. Tropical rainforest is vital ecosystem, i.e., it provide crucial ecosystem services such as raw materials, reservoirs of biodiversity, soil protection, sources of timber, medicinal plants, carbon sequestration, and watershed protection [7][8][9].

Threats to tropical rainforest
Tropical rainforest covers less than 10% of the land area of the Earth, representing the largest biological diversity reservoir, i.e., >50% of known plant species grow in tropical rainforest. Despite being rich in fauna diversity, every year, huge areas of tropical rainforests are being lost and degraded due to human interference [10][11][12][13][14][15]. It has been stated that 25-50% of the world's tropical rainforest has been lost and degraded due to the land-use change such as deforestation for palm oil plantations, agriculture expansion, cattle ranches, mining, and development of housing societies [16][17][18][19], while the rest of the rainforest areas is under a major shift in the dynamic structure and productivity.
It has been reported that Southeast Asia had the highest rate of land-use change (such as deforestation of tropical rainforest for conversion into oil palm plantation, commercial logging for timber and development of human settlement) as compared to other regions [12,[20][21][22]. Deforestation and fragmentation due to agriculture expansion, human settlement, logging, and fire had altered the plant species composition, richness, and diversity [23][24][25][26]. Deforestation and fragmentation, over-exploitation, invasive species, and climate change are the major factors due to which the biodiversity of tropical forest had declined at an alarming rate. For example, some of the fauna species became extinct, while others became threatened and vulnerable due to habitat loss, fragmentation, and degradation.
Changes in the vegetation structure and composition due to deforestation and fragmentation may alter the habitat suitability and food productivity. Habitat suitability, i.e., vegetation structure, species composition, species richness, canopy layers, and food productivity are key drivers, which predominantly influence fauna community parameters such as species composition, relative abundance, species richness, species diversity, and the density of tropical rainforest. Furthermore, it has been stated that the deforestation in humid tropic may be in the range of 4.9-5.7 million ha/year. Likewise, each year, 2.3 million ha of humid forests had been degraded due to logging and fire activities. Similarly, around 2.2 million ha/year tropical moist deciduous and 0.7 million ha/year tropical dry forest has been deforested due to anthropogenic activities [27].
Deforestation may cause habitat loss and fragmentation that adversely affect the population and the community parameters such as species composition, relative abundance, species richness, species diversity, and density of different wildlife species [28][29][30]. However, the effect of habitat loss and fragmentation on the wildlife species may vary depending on remaining vegetation and the surrounded landscape [31,32].
Land-use change such as deforestation, i.e., depletion of tree crown cover due to conversion of forested areas in agricultural fields, human settlements, excessive logging, and road constructions are major factors of habitat loss and degradation [10,33,34]. The habitat loss and degradation are responsible for biodiversity loss [35], low production of food, and habitat fragmentation [27,36,37] that ultimately affects different fauna species. Due to deforestation, large areas become isolated, i.e., temporal refuge, which serves as corridors for different wildlife species, especially bird species [38][39][40].

Floral composition
Tropical rainforests are the most rich tree species forest on the Earth and encompasses of broad-leaved trees with large buttress, and covered with climbers, epiphytes, and hemi-epiphytes. They have multi-layered canopy, i.e., upper, middle, and dense understory vegetation composition and are rich in diversity of flora and fauna, especially birds, mammals, reptiles, amphibians, and invertebrates [41][42][43][44]. Tropical rainforest is blessed with an enormous variety of flora species. The vegetation species composition of rainforests encompasses of four distinct layers of trees, namely; emergent, upper canopy, understory, and forest floor.

Emergent vegetation layer
Emergent or sunlit layer is dominated by broad-leaved, hardwood and evergreen. The trees may attain the height from 30.48 to 76.2 m and a trunk size up to 4.48 m around. The winds and sunlight are major environmental factors, which play a significant role (such as pollination and seed dispersal) in the tropical rainforest management ecosystem. The emergent layer is rich in the fauna species, such as birds (hummingbirds, macaw, harpy eagle, etc.), mammals (i.e., monkeys, bats, etc.), snakes, and insects such as butterflies, moths, etc. The birds and insects play a crucial role in the pollination of tropical rainforest plant species. The microclimate of this layer often fluctuates from time to time depending upon temperature and wind speed.

Canopy layer
The canopy is the main layer of tropical rainforest ecosystems, which is thick and dense like an umbrella. This layer is composed of a variety of vegetation structures and tree species composition such as philodendron, strychnos toxifera, rattan palms, etc. The trees may grow up to 18.29-27.42 m above the forest floor. Epiphytes such as orchids, mosses, ferns, and lichens are a common feature of this layer, which grow on tree trunks and branches. The canopy layer is rich in food diversity and an ideal habitat for a wide range of fauna species such as birds, mammals, reptiles, amphibians, and diversity of insect species. The members of fauna species are often observed flying, jumping, gliding, and hoping for canopy gaps.

Understory layer
The understory layer encompasses usually small trees, shrubs, ferns, and native bananas, which may attain 3.66 m height. Mosses, fungi, and algae often grow on the trees. This layer is rich in insects, such as bees, stick insects, ants, beetles, and butterflies, which serve as sources of food for a wide array of birds and reptiles. The fauna species encompass bats, monkeys, snakes, lizards, jaguars, frogs, and invertebrates.

Forest floor
This is the bottom layer of tropical rainforest. This layer is dark due to dense ground vegetation and only 2% of sunlight reaches the floor. Due to less availability of sunlight, only few plant species can grow. This layer is rich in organic matter such as fallen leaves, seeds, fruits, and branches. Furthermore, this layer is rich in fungi and mosses. The fauna species of the forest floor include elephants, tigers, pumas, leopards, jaguars, ocelots, mongoose, tapirs, cassowaries, okapis, armadillos, pigs, and gorillas.

Environmental services provided by fauna in tropical rainforest
Faunas are the important component of the tropical rainforest ecosystem and provide a wide array of environmental services such as; they keep tropical rainforest systems in balance through pollinating a variety of plant species, dispersing seeds, controlling pest population and reducing the damage caused by different pest species, scavenging carcasses, and recycling nutrients back into the soil.

Fauna composition
Fauna species are not only confined to specific habitats but also utilize various habitats in search of food, shelter, and reproduction. Tropical rainforest is rich in fauna species such as birds, reptiles, mammals, amphibians, and invertebrates.

Bird species composition of tropical rainforest
Birds are highly motile animals, i.e., they may fly to different areas in search of food, shelter, and for breeding purposes. They are ecologically diverse and had occupied a wide array of habitats. Bird species depend on the vegetation structure and composition (such as trees, shrubs, and herbs) and food resources for their survival and reproduction [45,46]. They are the functional group of tropical rainforest ecosystems as seed dispersers, pollinators, top predators, pest control, and scavengers [47][48][49][50].
Birds are conspicuous and an important component of tropical rainforest ecosystems, often exhibit distinction associated with vegetation structure and composition (Figures 2-4; Table 1). They are sensitive to habitat alteration and landscape modification [51][52][53][54]. This might be because the vegetation structure and composition may influence habitat selection and foraging efficiency of all birds. For example, large trees and ground dense herbaceous vegetation layers often harbor a higher avian abundance and diversity. This might be because old growth stands provide suitable nesting and breeding sites, plenty of food resources, and also provide  protection from predators and harsh weather [55,56]. Likewise, ground vegetation also offers ideal habitat and safe breeding sites and shelter for different fauna species residing in dense ground cover vegetation, such as birds, mammals, reptiles, and amphibians. It has been illustrated that height and density of the tree [57], dense understory vegetation [58,59], and logs and snags [60] are key elements, which affect avian distribution, richness, and diversity in tropical rainforest.
Habitat alteration due to land change use may alter the avian community parameters such as relative abundance, species richness, species diversity, and density [65]. This might be that bird community structure strongly associated with canopy openness and understory vegetation  Gerygone magnirostris

Copsychus saularis
Oriental Magpie Robin [6,63] Family Scientific name cover. Forest logging [66][67][68], habitat degradation and fragmentation [69], slash-and-burn agriculture [61], and fires are major factors, which had adversely affected the population of the avian species in different forest ecosystems [51]. These factors altered the vegetation structure and composition, which affects the avian richness and diversity by affecting the food resources, increased nest predation and brood parasitism. The diversity and richness of food resources are closely associated with the vegetation structure and composition, such as foliage, flowers, fruits, and barks. Furthermore, large-scale logging for valuable timber harvesting,

Golden Bat
Tropical Rainforest (Mexico) [73] Fauna Diversity in damage to forest, and replacement of native vegetation by exotic species [70] are the main problems, which affect the fauna species. Loss of forested areas is responsible for the loss of biodiversity.

Mammal species composition of tropical rainforest
Tropical rainforest had harbored rich mammal diversity and density due to richness of plant communities and higher productivity (Figures 5 and 6; Table 2). Mammals are a versatile group of animals and a major component of the tropical rainforest ecosystem, i.e., they serve a wide range of ecosystem functions; such as pollination, seed dispersal, pest control, herb control, food source for other animals and nutrient cycling. In addition to ecological  functions, the mammals also provide a wide array of benefits to human beings, such as food, recreation, and source of income, i.e., various byproducts such as bush meat, skin, oil, musk, fur, etc. [71,72].
Unfortunately, these rich mammal communities are facing severe threats from human activities such as over exploitation (intensive hunting), land-use change (habitat loss and degradation), and climate change [76][77][78]. These populations of different mammal species had declined abruptly due to change in land use, i.e., habitat fragmentation and degradation due to logging, and deforestation and habitat loss due to agriculture expansion and excessive hunting [79][80][81][82][83].
It has been reported that around one-fifth of mammal species in the wild are at risk of extinction due to human activities such as deforestation for agriculture expansion, logging for timber, and excessive hunting [84]. It has been stated that changes in vegetation cover may affect the richness of food resources and habitat preferences of the mammalian species [85,86]. This could be due to fact that home range preferences of the mammal species and their population are strongly associated with the vegetation structure and composition [87].
The primates residing in a rainforest are habitat specific, some occupy large continuous forested areas such as Diademed Sifakas-Propithecus diadema-while others prefer fragmented forested areas such as Black Howler Monkey-Alouatta pigra-for their survival and reproduction [25,[88][89][90]. Monkeys are diet specific, they consume a variety of food resources such as fruits, seeds, flowers, leaves, arthropods, etc. [91,92], and their diet is strongly influenced by the plant species composition and richness of the particular dwelling habitat [93].

Reptile species composition of tropical rainforest
Reptiles are carnivorous in nature and play a significant role in controlling various pests present in the forest, such as beetles, arthropods, caterpillars, termites, bugs, rats, mice, etc.,  Hylarana glandulosa

Rough-backed Forest Frog
Tropical Rainforest (Philippine) [94] Family Scientific Name Common Name
List of amphibian species that occur in tropical rainforest.
which may cause severe loss, such as defoliation, seed, and wood damage. Even though they are crucially important for tropical forest ecosystems (Table 3), they are facing critical threats from human induced factors such as land-use change (i.e., deforestation, fragmentation and degradation) that have altered the natural habitat of the reptile species that directly or indirectly depend upon tropical rainforests for their survival and reproduction.
Reptiles are highly sensitive species compared to other fauna species, i.e., they become more vulnerable due to land use change, i.e., habitat alteration [95]. This might be because they have a small home range, which is adversely affected by habitat loss and degradation [96,97]. For example, deforestation may cause severe habitat loss, fragmentation, and degradation which adversely affect the population, community parameters of reptiles inhabiting in a tropical rainforest ecosystem [98][99][100].
Anthropogenic activities had altered the reptilian intact habitat through land-use change, their habitats becomes degraded and lost thus ultimately becoming unsuitable for them. This is because forested reptile prefers dense and moist habitat, which provides them shelter and rich food resources for their survival, protection, and reproduction. Deforestation may disturb their breeding sites, reduce home range, and increase visibility for predators. Likewise, fragmentation reduced their home range, while degradation reduced their food resources and breeding behavior. Furthermore, land-use changes such as deforestation, fragmentation, and degradation may alter microclimatic conditions of particular dwelling habitats such as temperature, relative humidity, rainfall, and sunlight that ultimately modify the vegetation structure and composition.

Amphibian species composition of tropical rainforest
Amphibians are cold-blooded vertebrates and are carnivorous in nature. They play a key role to control the various pests, thus balancing the nature [101]. Amphibians are a significant component of the tropical rainforest ecosystem (Figure 7; Table 4) and play an important role in pest control. Habitat loss due highest deforestation is responsible for one-third population decline of the amphibians [10,[102][103][104]. One-fifth amphibians of Southeast Asia are reported as threatened species [105]. This is because they have small home ranges, i.e., specific aquatic habitat, higher vulnerability to habitat change, and visibility to predators. In addition, over-harvesting from natural habitat for food supply (human consumption), medicine (traditional use), and pet trade also had exerted great pressure on the population of amphibians [104].

Invertebrate species composition of tropical rainforest
In tropical rainforests, logging creates gaps and alters the habitat structure and microclimatic conditions, e.g., temperature, relative humidity, and light [107,108], which influence on the invertebrate diversity and distribution. After logging, new habitat with a different microclimate may develop which tend to be unsuitable for a wide array of invertebrates [109,110]. This indicates that land-use changes influence invertebrate diversity, richness, and distribution. It has been stated that disturbing the habitat affects invertebrate colonization and distribution [111,112]. Basset [113] reported that the canopy of tropical rain forest is rich in Coleoptera, Hymenoptera, Lepidoptera, and Araneae taxa. However, their home range and foraging habitats may vary from species to species depending upon the types of vegetation, forest types, and bio-geographical regions.

Conclusion and future perspective
Even though, faunas are a crucial component of tropical rainforest ecosystems, detailed information on different aspects of fauna community parameters such as species composition, distribution, diversity, richness and population trend, impact of anthropogenic activities, associated with microclimate and habitat variables is still lacking. The current review highlighted that tropical rainforest is an ideal productive habitat for a wide array of fauna species, i.e., birds, mammals, reptiles, amphibians, and invertebrates. These fauna are a major component of the food web of the rainforest ecosystem and functions. Furthermore, it was revealed that the diversity of rainforest fauna is facing many threats that directly or indirectly affected the population; community parameters of various fauna species inhabited the tropical rainforest.
There is an urgent need to study various fauna species of tropical rainforest in order to reduce the impact of human activities and for future conservation and management. We hope that the findings of this chapter will provide the ways and means to conserve the fauna in and around the tropical rainforest.