Tropical Forests Are An Ideal Habitat for Wide Array of Wildlife Species Tropical Forests Are An Ideal Habitat for Wide Array of Wildlife Species

Tropical forests are one of the most diverse (1 ha may contain more than 1000 plant species) and highly productive ecosystems on the earth. They cover 15.0% of the earth ’ s surface and harbored 80% terrestrial biodiversity. Tropical forests are home to thousands of endemic, rare, endangered, and threatened wildlife species, which play a significant role in ecosystem functions, such as pest control, pollinators, and seed dispersal. Wildlife species are bioindicators of the tropical forest ecosystems, that is, their presence or absence may provide the information about the habitat dynamics, such as vegetation structure, food resources, productivity, and anthropogenic disturbances. Despite being rich in wildlife resources, tropical forests have been extensively lost and degraded by human inter- vention, and their destruction is still continuous in a variety of ways. The current information on the tropical forests as an ideal habitat for a wide array of wildlife species is inadequate. It is highly essential to examine with solid grasp the suitability of the tropical forest as attractive habitat for diversity of wildlife species to understand their functional role fragile forest ecosystem and to formulate the better conservation and management strategies in future.


General background
Tropical forests are located at tropics of Cancer 23 N and Capricorn at 23.5 S to equator ( Figure 1) [1]. Around 60% of the tropical forest occurs in Latin America, 25% in Asia-Pacific regions, and rest 15% in Africa [2]. These forests covered <5.0% of earth's surface and comprised of 17,000 million ha, which is equal to 44.0% of the world's forest cover and exhibits a higher richness and diversity of flora and fauna species. Tropical forests are rich in vegetation composition and structure (Figure 2), which has formulated heterogeneity of habitats to attract the wide array of wildlife species to inhabit and utilize the food resources in order to perform various activities and to increase the numbers of their individuals [3]. The richness and diversity of vegetation could be due to the heterogeneity of topography, site quality, rainfall pattern, and temperature [4][5][6][7][8][9].
Tropical forests are intact habitats, which are rich in vegetation diversity and food resources that have attracted higher diversity of endemic, rare, threatened, and endangered wildlife species (i.e., such as mammals, birds, reptiles, and amphibians). The wildlife species directly or indirectly depends on tropical forests to perform various activities, such as inhabit, forage, loaf, perch, and breed for their survival and existence. Determining the wildlife population community parameters in the tropical forest habitats is vital important to understand the dynamics of the tropical habitat, ecological processes, and habitat disturbance vital for the occurrence, survival, and conservation of wildlife species.

Types of tropical forests
Tropical forests encompass 60% tropical rainforest, while remaining 40% are comprised of seasonally dry tropical forest, mangroves, tropical freshwater swamp forest, dry forest, open eucalyptus forests, tropical coniferous forest, savannah woodlands, and montane forests [10][11][12]. The tropical forests have been classified as (i) tropical moist broadleaf forests, (ii) tropical dry broadleaf forest, and (iii) tropical coniferous forest. The detail of each forest type has been given below:

Tropical moist broadleaf forests
These forests are the huge area located at equatorial belts between the tropics of Cancer and Capricorn dominated with semi-evergreen and evergreen deciduous tree species. They receive >200 cm rainfall annually [13]. The tree canopy is multilayered, that is, upper story (emergent crown), medium layer, lower canopy, shrub layer, and understory. These forests are home for more than 50% of world wildlife species. The occurrence of higher number of wildlife species is due to diversity of vegetation (i.e., >1000 plant species/km 2 ) and multilayered vegetation structure. For example, upper story is suitable habitats for apes, monkeys, flying squirrels, and birds (i.e., flycatchers), the understory layer harbored diversity of mammals (big cats) and avian species, (i.e., babblers, bulbuls, and pittas, etc.), while undergrowth vegetation is ideal habitat for gorillas, deer, amphibians, snakes, and lizards.

Tropical dry broadleaf forests
Tropical dry broadleaved forest is characterized with warm temperature and seasonal rainfalls that enable flora to withstand in rainy season as well as dry season to conserve water and shedding their leaves. These forests are located at tropical and subtropical latitudes, such as southern Mexico, Africa, the Lesser Sunda Islands, Central India, Indochina, Madagascar, New Caledonia, Eastern Bolivia and Central Brazil, Caribbean, North Andes, Ecuador, and Peru. They cover about 6 million km 2 or 4% of the Earth's surface [14] and are dominated by teak, ebony, bamboo, and fig trees [15]. The soil is highly productive, and tree canopy may attain 10-30 m tall. Tropical dry broadleaved forest is suitable habitat for mammals (white-fronted capuchin monkeys, mantled howler monkeys, shrews, bats, coyotes, foxes, ringtails, raccoons,

Ecological importance of tropical forests
Tropical forests provide diverse ecosystem services, such as play major role in water cycle, that is, they return around 90.0% precipitation into the atmosphere in the form of water vapors, increase the life span of dams through reducing the sediments into rivers, mitigate the disasters through reducing soil erosion and land sliding, and reduce the intensity and severity of floods [17]. Tropical forests are vital important for human well-being, that is, they contribute major proportion in food security (i.e., around global crops and one-third food supply depend on wild pollinators), regulate weather condition, reduce the negative effects of climate change by acting pollution filters, and serve as storage biodiversity. It has been stated that tropical forest may harbor >50.0% of world's terrestrial animal species [18]. Tropical forests play a crucial role in climate change, that is, the vegetation of tropical forest stored a huge amount of carbon taking from the atmosphere and stored in their various parts of the body (i.e., in leaves, stems, and roots, etc.) and serves as mega carbon storehouse or sinks (e.g., 25% store of world's carbon). It has been known that tropical forest can store huge amount of carbon compared to those they release back into atmosphere, slow down the rate of carbon dioxide accumulation in the atmosphere, and reduce the effect of climate change. Hence, this indicated that tropical forests play a significant role to reduce the effects of climate change and reduce 12% emission of greenhouse gases into the atmosphere. Wildlife species are the essential component of the tropical forest ecosystem, that is, they play a major role, that is, pest control, pollination, and seed dispersal in tropical forest ecosystem [19]. At habitat level, the occurrence and richness of wildlife species represent a powerful tool to examine the current status of particular ecosystem. This could be that wildlife species are ecologically specialized in habitat use, diet, and highly sensitive to habitat and microclimate alteration [20][21][22].

Threats to tropical forests
Currently, tropical forests are facing severe potential threats due to human interventions, such as extensive habitat loss and degradation, isolation, and fragmentation due to heavy exploitation and conversions into agricultural fields and residential areas [29][30][31], which create a complex spatial disturbance [32][33][34]. More than 50% of the tropical forest areas have been lost during the past two decades through extensive deforestation for timber, fuelwood, agricultural expansion, and human-induced fire [35][36][37].
It has been stated that habitat loss and fragmentation of tropical forest is a major threat for wildlife species composition, relative abundance, species richness, and density, that is, it increases higher predation risk, reduced food occurrence and diversity, and genetic variability of birds, mammals, amphibians, and reptiles [38][39][40][41][42][43]. This may alter habitat thus makes it less productive and attractive thus caused the shift of wildlife species into human-dominated landscape that might be unsuitable and less productive for them [44][45][46][47][48]. However, the consequence of habitat loss and degradation may vary from species to species depending upon the nature and extent of habitat alteration, availability of food resources, and the rate of predation and parasitism [49,50].
In addition, climate change is an important factor, which has effects on wildlife species phenology, geographic distribution, physiology, vegetation composition, and food resources [51,52]. Thus, it ultimately exerts negative effects on the population community parameters of the species, i.e., some becomes endangered, vulnerable, and threatened [53][54][55]. This might be that the climate change may cause the rising of temperature and declining of the precipitation, which make the tropical forest dry and highly susceptible to fire and prone them into shrub lands, grassland, and savannah. The alteration in microclimate may alter the vegetation species composition, richness, and diversity [56,57].

Birds of tropical forests
Tropical forests are more diverse in vegetation structure and composition, which offer higher habitat complexity, that is, provide a diversity of nesting sites, greater protection from predators and harsh weather, and also plenty of food resources [58]. The vegetation climax and diversity had attracted a wide array of avian species, which are habitat and diet specialist in nature. For example, Black-naped Monarch-Hypothymis azurea-often prefers canopy and foraged on flying insects, Blue-headed Pitta-Pitta baudii-prefers to utilized the ground vegetation of evergreen broadleaved forest and prey on caterpillars of insects occurs in grasses, and Scarlet-rumped Trogon-Harpactes duvaucelli-is middle story bird often associated with evergreen broadleaved vegetation ( . They prefer to utilize old mature trees (large diameter and height) for foraging and nesting [59,60]. Avian species often play a crucial role in forest ecosystem functions, that is, they pollinate the flowers and disperse the seeds from one   part of the forest to another [61][62][63] and control the pest such as rodents, insects, and squirrels, which may cause damage to the forest foliage.
Tropical forest birds are vulnerable to habitat loss, fragmentation, and changes in land use patterns [64][65][66][67]. This could be that habitat loss and fragmentation may alter the vegetation structure and composition, reduce the food resources, increase predation and brood parasitism risk, and enhance the competition for food and space [68][69][70][71]. It has been illustrated that in Southeast Asia, tropical forests are facing highest rate of habitat destruction [72][73][74][75][76], which exerts immense pressure on the habitat use, foraging behavior, and breeding success of avian species (Table 1).

Family
Scientific name Common name Reference

Mammals of tropical forests
Mammals are crucial element of tropical forest ecosystems [78,79]. They exhibit a wide range of niches, exploit diverse tropical forest resources, and play a crucial role in vegetation composition and ecosystem functions, i.e., they forage on the grasses, control weed, pollinate flowers especially bats, and disperse seed from one area to another area after consuming in the form of pallets [63,[80][81][82][83].
Mammals are considered the third most threatened and endangered animals, for example, Mantled Hawler Monkey-Alouatta palliata-and Amazonian Tapir-Tapirus terrestris- (Figures 6 and 7) due to habitat loss and destruction, illegal hunting, and trapping [84][85][86]. It has been stated that >30% mammal species are threatened and their population is still declining day by day through a variety of ways [87] ( Table 2).   Bovidae

Amphibians of tropical forests
Amphibians are most abundant vertebrate in tropical forests, that is, they vary in color, behavior, habitat selection, size, and population density. Tropical amphibians are widely distributed and habitat specialist animals, that is, they often prefer the riparian areas of tropical forests ( Figure 8). Amphibians depend on multiple environmental gradients and are closely Family Scientific name Common name Reference
The loss of amphibians seriously disturbed ecological function of tropical food chain and food web. This could be that they are important component in tropical food web, that is, have occupied diverse niches from planktivore to carnivore and often serves as major sources of food for wildlife species in tropical forest. From the ecological point of view, they are best indicators of habitat fragments, ecosystem stress, and aquatic pollution, etc. In addition, amphibians have been used in ecological, embryological, physiological, and genetic research purposes.
One-third populations of amphibian species had been listed as threatened and endangered due to human intervention [91,92]. Habitat characteristics [93], habitat fragments due to forest logging [94][95][96][97][98], habitat loss and degradation [99][100][101], environment variables [102], invasive predator species [103], diseases [104], and leaf litter [105] are major driven factors which effect on amphibian assemblages and population parameters. However, the effect of these driven factors may vary depending on the nature of the habitat disturbance, change in microclimate, and alteration in food resource. This could be that the leaf litter, canopy cover, tree size, stream size, availability of river, and refuge areas are highly essential for their survival and reproduction (Table 3) [106,107].

Reptiles of tropical forests
Tropical forest is diverse and complex ecosystem which harbors most abundant and diverse reptile species [112]. Reptiles are primary consumers, that is, they prey on many animal species, such as birds, mammals, and amphibians ( Figure 9). They provide ecological services into tropical forest ecosystem, such as control the population of pest (i.e., insects, rodents, Figure 8. Silver long-fingered frog-Cardioglossa leucomystax.
Reptiles are facing severe threats due to human activities, that is, habitat loss, and indiscriminate trapping and hunting for their skin and food thus become threatened and endangered [116][117][118]. The population decline of various reptile species in tropical forest may cause ecological imbalance that effected on the ecological functions (Table 4) [119,120].

Varanus bengalensis
Clouded monitor lizard [121] 6. Conclusion In conclusion, this review has attempted to highlight that the tropical forests are ideal habitat for a variety of wildlife species, especially birds, mammals, reptiles, and amphibians. This might be due to the occurrence of heterogeneity of vegetation structure and composition, richness and diversity of food resources, safe breeding and nesting sites, and shelter from predators and harsh weather. These forests should be kept intact, preserved, and managed scientifically on a sustainable basis to reduce the human interference and for future generation.

Recommendation for future research and conservation
Furthermore, in future, a detailed research on the wildlife ecology should be carried out by investigating the effects of independent environmental variables with respect to the habitat selection and association, vegetation structure and composition, home range and distribution, population parameters, occurrence of food resources and distribution, influence of human interventions on wildlife population, habitat disturbance, etc. This will help to identify the threats facing different wildlife species and their habitats, indicate the current status of wildlife population within the landscape, and determine the productivity of the particular area.