1 Introduction

The interaction between humans and the environment has undergone significant changes over the years due to urbanization. Developing nations, characterized by rapid population growth, have also experienced notable economic development strides. However, this rapid development and human amplification has also cause both socio-economic and environmental issues such as the increased effects of climate change, environmental quality degradation, land conversion, and deforestation, which were mainly found in urban centers in the world [1, 2]. The drastic changes in urban ecosystem fueled the need for multi-disciplinary approaches in studying the complex interactions between socio-economic and the environmental factors, as urban areas were also considered to be the frontlines of both environmental and sociological changes, making the research on understanding the mechanism of ecological processes in the cities significant [3,4,5].

In the founding years of urban ecology pioneered by Park et al. [6], the field was developed as part of human ecology, delving into the relationship of people and the urban environment. It was also considered as a broad body of knowledge encompassing urban changes in the perspective of human influences [7]. As the concept of contemporary urban ecology emerged [8], it became an approach that cuts across a wider perspective looking into social sciences, sociology, geography, social ecology, and urban planning, emphasizing on the interdependence of each component of the urban ecosystems. Throughout the years, each aspect of urban ecology has been further delineated to new and clearer approaches, composed of human behavior and organization in cities (human ecology-based approach), distribution of plants and animals (bio-ecology), ecosystem-wide perspective with natural and socioeconomic components (urban systems approach), and spatial heterogeneity and dynamics of urban ecosystems (urban landscape approach) [9,10,11,12,13,14,15]. As urban ecosystems are complex dynamic of biological-physical-social entities, ecological studies have emerged as an interdisciplinary field wherein researchers in multiple fields come together for the growing knowledge of the society ranging from the field of sociology, economics, and environmental sciences) [3, 16,17,18,19,20]. In light of the continuous growth of urban areas, the illumination of research studies in urban ecology is the gateway for the more profound understanding of urban ecosystems and science-based solutions for sustainable urban development, as urban ecology is not limited to the discovery of ecological patterns, but also supporting the ecosystem services for the benefit of urban residents and a path towards biodiversity-friendly in urban areas [21,22,23].

In Southeast Asian countries such as the Philippines, tourism, urbanization, and globalization are the main drivers of economic growth. However, biodiversity hotspots such as the country are more prone to the profound effects of the increase in urban areas, as alterations of natural disturbance regimes and processes can be detrimental to ecological communities, leading to reduction of floral and faunal density, which in turn have consequences to the ecosystem services for humans [24,25,26,27,28]. As economic development is mainly focused on the urban areas in the country, studies have shown that an increasing percentage of the Philippine population resides in the cities compared to rural areas, which is also projected to increase in the next few years [29]. Such urban migration of people from the rural areas of the country has led to the increasing urban sprawl in many regions of the Philippines [30, 31], alarming increase in urban heat islands [32], deterioration of air and water quality, pollution, conversion of land and water bodies, increase in human population, and increased risk for human health [20] and a decrease in biodiversity due to the loss of green spaces in many parts of the metro. Mitigating strategies have been implemented to prevent the continued detriments in Philippine urban cities through the development of urban ecology.

As an archipelago composed of more than 7000 islands with a surface area of approximately 300,000 square kilometers, and home of complex geologic positions and history, the Philippines is as country of rich biodiversity yet one of the most environmentally threatened in the world. In addition, the archipelago houses a wide variation of habitats such as coastal plains, mountain ranges, volcanic areas, a rainforest, making it a home for an estimate of 20 percent of the world’s known species of both flora and fauna [31,32,33]. Amidst the rich biodiversity and ecosystem services offered by the archipelago, the country faces anthropogenic threats such as deforestation, agricultural expansion, and increasing rate of urbanization which resulted to the drastic alteration of the land cover [34, 35]. Similar to other developing countries such as India, Thailand and Vietnam, the rapid urbanization in the Philippines is accompanied with major challenges when it comes to urban environment management and socioeconomic issues such as poverty, transport system, sewage and sanitation, supply of basic needs, and lack of prioritization in urban development [36]. Moreover, the urbanization in the country is mainly concentrated in the national capitals, which in turn creates both an environmental and socioeconomic imbalance instead of a gradation from rural to urban areas. Specifically, the rate of urbanization was centralized in Metropolitan Manila, Metropolitan Cebu, and Metropolitan Davao which house most of the countries’ population amidst the limitations on their surface area [37].

As the nation continues to experience the effects of rapid urbanization, the urgent need in assessing and synthesizing the existing studies can serve as critical foundation for an evidence-based decision-making and formulation of policies, fostering the coexistence of increased human population and the urban ecosystem. Since the emergence of urban ecology, the enhancing of knowledge on how ecological communities respond to urban pressures can address the questions that may arise in terms of urban biodiversity [38]. As the first comprehensive review of urban ecology in the Philippines, this paper aims assess the current scientific knowledge in the country in the field, identify the knowledge gap and potential target research efforts and facilitate the integration of ecological principles into urban development planning and strategies. By means of shedding light into the interplay of biodiversity, urban residents, and the urban environment in the Philippines, this review serves as a tool in advancing the knowledge in urban ecology in the country. Hence, to determine the status and progress of urban ecology research in the country, this study aims to review all published papers related to Philippine urban ecology. Specifically, this paper determined and analyzed the prevailing spatial and temporal patterns and trends in urban ecology in the Philippines. Consequently, the methodologies that were employed in studying urban ecology in a local context were enumerated. Through the synthesis of the current available studies, the knowledge gaps in the field were highlighted to serve as a guide for potential priority areas needed to be studied. This paper also discusses the major themes in Philippine urban ecology encompassing landscape ecology, environmental quality, biodiversity, socioecological studies, and sustainable development. With these, this comprehensive review can provide a concrete assessment of the current state of urban ecology studies in the Philippines, which in turn can help future researchers, stakeholders, and policymakers in decision-making processes based on science-based approaches and prospective fields to study further.

2 Materials and methods

To assess the current state of urban ecology research in the Philippines, and how the knowledge in Philippine cities emerged throughout time, revisiting previous research and findings must be conducted. In this paper, a systematic review is conducted to synthesize what has been known about the field and the future directives of urban ecology by means of identifying trends and research gaps. Since systematic reviews primarily aid in summarizing the results in a quantitative and qualitative approach through a comprehensive literature review, they can further deepen the understanding regarding the topic of interest [39, 40]. By principle, systematic reviews follow the necessary steps: research question formulation and identification of review scope, data collection and filtering, and summarization or synthesis of all the research studies gathered.

2.1 Data acquisition

Four primary databases were used to gather relevant papers for data analysis: Scopus and Web of Science, ScienceDirect, and Google Scholar. For article extraction, the keywords inputted were “Urban Ecology in the Philippines,” “Urban Ecology,” AND “Philippines.” The inclusion criteria were the following: (1) articles must be written in the English language, (2) studies must be conducted in the Philippines or included in the Philippines in the scope, (3) the research abstract must contain at least any of the keywords, and (4) must be a published research article in a non-predatory journal. A total of 2487 articles were retrieved from the databases. The articles acquired were from the years 1982 to 2023. All records were retrieved using the PRISMA methodological framework (Fig. 1).

Fig. 1
figure 1

The PRISMA framework

Full size image

2.2 Data screening and eligibility

In terms of the screening process, the extracted studies from the databases were scanned for duplicates. In total, 17 duplicates were found. Consequently, the research articles were screened according to the established inclusion and exclusion criteria. Out of 2487 articles, a total of 105 articles were included in the analysis, which were reviewed, categorized, and synthesized. The research studies included were by the criteria set. They were in line with the primary theme of the systematic review, which is studies focusing on different areas of urban ecology in the Philippines.

2.3 Data analysis

A descriptive and thematic analysis was conducted to analyze the acquired articles comprehensively. For a more detailed summary of the data acquired, descriptive analysis can be an efficient tool for detecting data characteristics in simple percentages shown in visual summaries, which may influence the study’s conclusions [41]. For the descriptive analysis, the most cited studies, the year of publication, the scope of study areas, and the methodology used were taken into consideration.

Thematic analysis is mainly utilized in analyzing qualitative data, wherein the determination of patterns and trends in the dataset can result in a more comprehensive understanding, contributing to the results’ robustness [42]. Thus, thematic analysis was used to deal with categorizing the included studies into the major themes or areas of interest in the concept of urban ecology. Through familiarization, generation of themes, and reporting formed themes, researchers can segregate based on the focal concepts of the studies. After familiarizing and managing the records in Excel sheets, a more intricate and critical literature review was conducted to summarize and sort the articles into specific themes. Results and recommendations were formulated according to the gaps and challenges identified based on the descriptive and thematic analysis [43].

3 Results and discussion

3.1 Descriptive analysis

Through monitoring the progression of studies in urban ecology, an understanding of the dynamic relationship between urbanization and the environment can be achieved [21, 44,45,46]. As Philippine cities are continuously growing and evolving, tracking how urban ecology research evolves throughout enables the adaptation of strategies for sustainable urban development, biodiversity conservation, and the well-being of urban inhabitants. In terms of the annual number of publications, detailed analysis of how studies have grown over the period has been exhibited through a linear graph (see Fig. 2). It has been exhibited that the annual number of publications on urban ecology in the Philippines has increased along with time. The first published study relating to the field was on urban dominance, ecology, and community well-being in a Philippine region [47], which observed trends in the effect of ecological differences on the socio-economic status of a peri-urban population in urban communities. Although there has been an evident decrease in the published studies in 2021, during the peak of the COVID-19 pandemic, the continuous increase in urban ecological studies in the countries implies a growing interest in the field throughout the years. It has also been observed that there is a significant decrease in the number of studies in the current year of review, 2023, as the year has yet to conclude. Although there has been a growing emergence of urban ecology studies in the country, the variations of methods and limitations of scope areas is still for improvement.

Fig. 2
figure 2

Number of annual research papers on urban ecology in the Philippines

Full size image

As the development of urban ecology research in the Philippines continuously emerges, looking into the topmost cited papers serves a significant role as the fundamental principles, methods, and findings of these studies serve as sources of the interplay of urbanization and ecological dynamics in the country. Based on the data obtained as of August 2023 (see Table 1), the most cited studies dealt with urban landscape ecology and the effects of urbanization on the landscape, which encompasses issues such as land use and land cover changes and the increasing temperatures in urban areas, otherwise known as the Urban Heat Island Effect (UHI Effect) [48,49,50,51,52,53]. In coherence with the results, studies have shown that studying urban ecosystems in a landscape scale as it provides framework in understanding urban ecosystems in consideration of whole cities in a regional context; in this manner the elements of sustainability science is perceived more comprehensively and effectively [54, 55]. The changes in the ecosystem services along with urbanization have also been highlighted by the study of Estoque & Murayama [56], which brought light to the relevance of building sustainable cities. Based on the most cited studies, the scales of studies are either in a regional sense, whether it be Southeast Asian countries or the whole Philippines as models. Few studies have focused on a city-specific scale and were conducted in the most known cities such as Metropolitan Manila, Baguio City, and Subic Bay. Although these cities vary in terms of geographic features, Manila being in the lowlands, Baguio City in the highlands, and Subic Bay as a representation of cities located along the coastline, giving more attention to not just mainland Luzon will be plausible for the representation of both geographical and sociological conditions of the islands in Visayas and Mindanao.

Table 1 Topmost cited articles from the selected Philippine urban ecology studies
Full size table

As cities or urban centers are considered complex ecosystems with varying characteristics that are altered spatiotemporal, the continuous expansion of knowledge and urban ecology comes with a comprehensive investigation of urban areas [21, 57].To be able to detect what type of studies and where urban ecology research were conducted, the distribution of urban ecology studies in the Philippines were subdivided into four major themes in accordance with the fundamentals of urban ecology studies, namely: urban landscape (landscape ecology), urban systems (environmental assessments), bio-ecological (biodiversity studies) and human ecology-based approach (socio-ecological dynamics). These themes are further described in the thematic analysis. Among the 149 cities in the Philippines, 21 cities were identified as urban ecology research study areas (Fig. 3a).

Fig. 3
figure 3

Distribution map of urban ecology studies in the (a) Philippines and (b) Metro Manila

Full size image

Twelve studies were conducted from a country-wide perspective, and most of the studies were conducted within Metropolitan Manila (Fig. 3b), mainly studying the socio-ecological dynamics of the cities. The top studied cities were Quezon City, Manila City, Baguio City, Cebu City, and Davao City. These areas are the socio-economic centers of the country, ranging from Northern and Central Luzon, Visayas, and Mindanao. The Laguna de Bay was also one of the top study sites in terms of urban ecology, with a total of 9 studies included, as the lake is the largest freshwater body and most economically significant lake in the country, which expands through multiple provinces namely Rizal, Laguna, Batangas, Cavite, and Metro Manila [58]. Although the lake has been a significant water source for industries such as agriculture, aquaculture, transportation, recreation, and domestic use, its water quality has continuously deteriorated due to land conversion and anthropogenic activities, highlighting its significance for further research [59]. As observed, urban ecological studies were primarily done in the mainland Luzon, making the available information for grasp the country’s condition regarding urban ecosystem conditions inadequate, highlighting further assessments such as producing baseline information on the cities found in other islands of the archipelago. An insufficiency of available studies was exhibited in the islands of Visayas and Mindanao, wherein urban areas were also established, as each island has a city or urbanized capital. Although assessments of urban forests and parks are essential, giving light to informal green spaces is often neglected and must be addressed, as it also contribute to the overall environmental condition of urban ecosystems [60]. Thus, employing further studying cities in various spatial scales enables researchers to grasp the principles of how landscape size, configuration, and composition can indicate the need to employ urban ecological models in a multi-scalar perspective [55].

Scientific methods have been the primary guiding principle in the growth of research as they primarily prescribe activities that will yield the validity of studies and give a unifying concept of the approaches in the investigation of any field of natural sciences [61]. Urban ecology is a heterogeneous and multidisciplinary science encompassing environmental, biological, and sociological sciences with variable research approaches [21]. As urban ecosystems are primarily human-dominated, the history of the development of cities, the influencing factors, and the potential effects must be considered, which is vital for a deeper understanding of the nature of urban ecosystems [62].

Regarding the methodologies employed (Fig. 4), using survey questions and conducting interviews with stakeholders, management, and the general public were the most used methods (21.4%), as urban ecology mainly involves human activities and perceptions. Taxonomic surveys (18.3%), the profiling of species identity by means of looking at their biological and ecological characteristics, is related to studying ecology in describing ecological patterns, community structure, and the vital interactions and functions between organisms. Moreover, molecular approaches were also applied in studying urban ecology. As observed in the studies obtained, only a few significant studies have employed molecular techniques such as DNA fingerprinting, genomic surveillance, and isolation of microorganisms (4.6%). As taxonomic surveys provide essential data on the state of biodiversity of urban ecosystems, further exploring different taxonomic groups. With further taxonomic assessments, wider and more extensive data can be obtained. On the other hand, human surveys can go together with biological surveys as it helps assessing the socio-ecological dynamics in different cities as both environmental factors and socioeconomic factors are found to be influencing the species richness within urban communities [63,64,65,66,67].

Fig. 4
figure 4

Distribution map of the number of urban ecology studies in the (a) Philippines and (b) Metro Manila

Full size image

As urban ecology requires multifaceted approaches to understand both the biotic and abiotic dynamics in the environment, looking into a landscape perspective enables a more comprehensive understanding of the ecosystem. An emerging technology utilizing GIS and remote sensing is a breakthrough in urban landscape ecology (16.8%). The science of acquiring information through non-contact, geospatial technology enables researchers to obtain spatial information encompassing large spatial and temporal extents, which is instrumental in analyzing how landscapes are modified through time. However, the remote sensing applications that were primarily utilized focused on indices such as Land Use Land Cover Change detection and the changes in Land Surface Temperatures in urban areas. In fact more landscape characteristics can be assessed with the use of remote sensing in urban areas such as assessing the vegetation and greenspaces available [68,69,70], monitoring the air quality and pollution rate [71,72,73], planning transportation and infrastructure systems [74, 75], socioeconomic studies [76, 77], disaster management and resilience planning [78, 79] and even urban ecological modeling. As abiotic factors also play an essential role in urban ecology as they directly affect the environmental tolerances of organisms and the health of the residents, environmental monitoring in the form of chemical assessments of aquatic and terrestrial ecosystems has also been conducted (7.6%). However, environmental monitoring requires continuous temporal assessments as urban ecosystems may have drastic changes depending on the intensity of anthropogenic effects towards cities. An efficient method on employing continuous environmental monitoring is through employing an inclusive and solution-orientated community-based monitoring, as community members can also play a role in collaboration with the researchers for the communities’ deeper understanding of human–environment interaction [80].

Qualitative field observations (5.3%) were also done to monitor the state of urban areas focusing on primary issues addressed in urban areas, such as looking into the vulnerability and resilience of cities froRegardinghange effects, socio-economic state of agricultural and aquacultural industries, and the urban management frameworks and practices to maintain the overall environmental well-being of cities all over the country [81,82,83,84]. Lastly, Literature reviews (6.9%) have also included the country to assess the current state of Philippine cities mainly conducted in Metro Manila and Baguio City, both located in mainland Luzon, regarding socio-ecological dynamics, sustainable development, and significant health concerns concerning what is occurring in neighboring countries encountering similar challenges [85,86,87,88]. As qualitative methods were observed to have the least attention among all the methodologies employed, integration of more qualitative urban traits can expand the understanding on socio-ecological dynamics, which includes looking into the landscape and the sociological history of more cities in the country, for researchers to fully compare the state of the Philippine cities with neighboring countries.

3.2 Thematic analysis

Categorizing the studies gathered under different themes enables a generalized yet more comprehensive view of the country’s critical factors and aspects of urban ecology studies. Each of the papers was scrutinized, evaluated, and classified into four themes: urban landscape, urban systems, bio-ecological and human ecology-based approach.

3.2.1 Philippine urban landscape ecology

In the science of landscape ecology, a more interdisciplinary and holistic approach has emerged, integrating the theories of ecology and geography into the history, planning, conservation, and management of landscapes, along with human interactions that primarily use the landscape as living spaces. Moreover, this field of ecology generally investigates the interactions between spatial patterns and the ecological process from a broader perspective, primarily conducted regionally. It also delves into the concept of landscape heterogeneity, which focuses on defining landscape characteristics, which can be beneficial knowledge for landscape planning and urban sustainable development. For urban landscapes, studying how spatial heterogeneity changes or develops through time, along with the continuous alterations in both biotic and abiotic factors, is a vital field, especially if studies were made as a collaborative work between landscape ecology and urban planners. Compared to other fields, such as socio-ecological dynamics, landscape ecology treats human activities as part of the system rather than as a separate factor to the issues addressed.

Significant repercussions of urbanization were also highlighted in some landscape pattern studies highlighting issues such as urban sprawl, pollution, public transportation, increase in carbon emissions, and increasing temperature in urban centers due to the UHI effect mainly in the megacities in the country [48, 52, 53, 89]. In the urban landscape studies in the Philippines, researchers have highlighted the changes in land use and land cover of developing areas all around the country and related these landscape changes to the implications of current environmental management, ecosystem services, and habitat availability for the remaining biodiversity within the area, which are conducted in various areas such as coastal and highland cities such as Manila and Baguio City, consecutively [49, 56, 89,90,91,92]. With the integration of mathematical modeling and machine learning to GIS and remote sensing, researchers have also predicted future urban expansion and landscape changes based on the existing as a form of foreseeing for sustainable development planning to avoid the detrimental effects detected previously [59, 93, 94]. As the cited studies were only centralized in the urbanization effects in the megacities, additional analyses can also be done in the developing peri-urban cities as drastic changes may also occur throughout time. To make landscape ecology studies in urban ecosystems, landscape fragmentation can also be assessed to examine how urbanization can affect the connectivity of corridors, green spaces, and distribution of the suitable habitats to determine the flow of ecological processes in the landscape. The involvement of the residents through conducting social surveys and participatory mapping may also be integrated in landscape ecology studies for researchers and decision-makers can supplement social perceptions on future landscape planning and monitoring. Additionally, the use of GIS and remote sensing can also be applied in the identification of how environmental stressors are distributed in urban areas to identify priority areas in conservation and management.

3.2.2 Urban systems approach in studying Philippine cities

As the development rate of urban areas is continuously rising, its effect on socio-economic sustainability and environmental issues has been significantly evident, such as increasing demands for energy and natural resources [95, 96] increase in impervious [97, 98] surfaces further causing the UHI, degradation of soil, water, and air due to pollution and loss of vegetation [99,100,101,102] and lastly, the drastic decline of biodiversity due to reduction of natural habitats [103]. Thus, incorporating assessments to examine environmental quality can be utilized to be able to understand the interactions between various factors that can either negatively or positively affect the environment.

Water pollution is a significant concern for highly urbanized areas and any community as it is utilized in the household, industries, and as a source of livelihood such as fisheries. As water is the most crucial environmental component, as if it is a source of life and irreplaceable, sources such as lakes and rivers must be protected from pollutants and conserved to avoid future generations’ scarcity [104, 105]. However, the amount of waste disposed in water bodies results in contamination composed of various pollutants such as nutrients, pathogens, chemical and plastic products, and even industrial wastes, bringing the water supply and quality down [106]. In the Philippines, the detection of heavy metals and microplastics in water bodies nearby cities has been a significant concern raised from recent studies as it can affect the biodiversity of both freshwater and marine species and can also affect the health of the consumers [107,108,109,110,111]. It has been observed that most contaminations were specifically located near cities, most specifically from the untreated wastes from waterways connected to the lakes [110]. Aside from nutrient, physicochemical, and microbial analyses, the integration of molecular methods such as environmental DNA (eDNA) can also detect the presence of aquatic diversity. Hydrological modeling and remote sensing can also be conducted in understanding water dynamics, including how pollutants and water quality change in the gradient from the pollutant sources. Moreover, as some urban communities in the country are along water bodies, integrating citizen science in water quality monitoring can improve both the data acquisition and the awareness and involvement of urban residents in aiding the deterioration of water quality.

Aside from water quality deterioration, soil pollution can also significantly affect the urban ecosystem, which is due to the accumulation of solid and liquid wastes, industrial activities, and bioaccumulation of toxic chemicals, which poses a severe risk to biodiversity and human health, specifically acquisition of pathogens, carcinogens, and mutagens [112]. Quantification of metal concentrations in soil and plant samples were also done in Philippines cities to elucidate relationships between the property of soil substrates and the concentration of heavy metals in various land use classifications, which indicated that anthropogenic activities and disturbance brought about by rapid urbanization have caused increase toxic amounts in terrestrial environments [113]. To mitigate or eradicate these ecological risks, further studies and environmental assessments, in the form of either EIAs (Environmental Impact Assessments) or Strategic Environmental Assessments (SEA), can be useful for a higher level of decision-making and incorporating the data for sustainable development plans [114].

3.2.3 Philippines in a bio-ecological perspective

The biodiversity in a human-dominated system such as highly urbanized areas is considered a unique case as the introduction of exotic species was normalized due to the environmental tolerances of native species. Thus, species composition in artificial or modified ecosystems such as these can differ from those in rural areas. In addition, drastic environmental changes can significantly affect the species composition as anthropogenic activities and climatic conditions play a significant role in the distribution of various groups of organisms [115]. Nevertheless, a significant challenge in conducting biological assessments in urban environments emphasizes the requirement for additional data regarding urban habitats and the gathering of information on the presence of various species [116].

Recording and assessing the biodiversity in urban areas has long been conducted in the Philippines. These surveys encompass groups of organisms ranging from fungi, plants, insects, birds, mammals, and aquatic macroinvertebrates, investigating their food sources, spatial patterns, diversity, and how abiotic factors influence their occurrences in regions such as cities in Northern and Southern Luzon, Western Visayas, Metropolitan Manila, Metropolitan Cebu, Metropolitan [34, 117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134].In addition to mere taxonomic surveys, some of the studies, as mentioned earlier, utilized biodiversity indices as using biodiversity metrics such as species richness and evenness, which can be utilized to compare communities or populations either spatially or temporally, which highlights the importance of specific areas for environmental monitoring and conservation. However, continuous, and more comprehensive monitoring of the changes in species composition in relation to the increasing effects of urbanization still needs prioritization. In this manner, researchers and concerned organizations can implement improved strategies in conserving and protecting the natural flow of urban ecosystems. Employing formulation of a mechanistic framework in identifying the urban ecological processes, to shed light on the effects of urbanization to ecological interactions in the city centers of the country [135].

In coherence with taxonomic surveys, the use of DNA barcoding was also utilized in identifying ant species in urban areas [134]. In addition, the use of DNA fingerprinting and microbial isolations were also utilized to be able to assess the conditions of both aquatic and terrestrial environments through looking into both biotic and abiotic components [136, 137]. As health is also a significant concern in highly urbanized areas such as in Metro Manila, the use of molecular methods was also applied in pathogen monitoring such as dengue virus and pollen allergens [138,139,140]. Although ample biodiversity studies have been conducted, it has only been recorded in a few major cities in the country, mostly centralized in the metropolitan areas such as Metro Manila, Metro Cebu, Metro Davao and Baguio City as the most urbanized in Northern Luzon. It has yet to be conducted regularly to detect composition changes throughout time. Thus, more well-rounded assessments must be conducted for researchers and urban planners to understand further the natural and human-controlled processes that alter urban biodiversity, not just in the metropolitan cities, but also the emerging urban areas in island capitals.

3.3 The current state of human ecology-based research in the Philippines

Urban environments are considered heterogeneous landscapes, composed of socio-economic and ecological features, making a human-to-nature dynamic. This is where the concept of socio-ecological systems came into context, as it is an integrated system wherein human aspects such as their political, cultural, institutional, technological, and socio-economic characteristics play a significant role in the interaction with natural ecosystems, or simply the interaction between social systems with biogeophysical unit off the environment [141, 142]. As complex environmental problems also need complex forms of solution, studying the socio-ecological dynamics has been increasingly important in both scientific and policy communities, as researchers need to deal with a more integrative and interdisciplinary approach in studying both social and ecological systems [143].

Studying human perception and understanding were primarily utilized to perceive the communities’ standpoint on the current implementation, governance, and challenges in managing urban ecosystems [144, 145]. As urban centers also encounter socio-economic problems such as waste management, food supply, health concerns, overpopulation, and flooding, understanding the challenges faced by residents is also vital in studying the socio-ecological dynamics [146,147,148]. In acquiring direct information regarding the socio-economic status of the residents in the urban areas, primary aspects of socio-ecological systems can be detected such as their resilience, adaptability, vulnerability to environmental and economic changes, and lastly, the type of governance among communities, which are interrelated concepts in an ecological and sociological perspective [149]. Moreover, surveys were also conducted for socio-cultural and ecosystem valuation to be able to determine the significance of ecosystems in terms of their benefits in regulating, supporting, provisioning, and cultural services, which can be an instrument for strengthening conservation strategies in these areas [150,151,152]. Thus, to improve the understanding towards the flow of ecological communities in cities, the demographic, culture, and economic activities must be considered, looking into the approach of urban ecology in a sociological approach, as human behavior and social organization of cities play a significant role in urban ecosystems as a whole.

3.4 The potential and future directives of Philippine urban ecology towards sustainable development

As previous studies have addressed significant issues regarding the current state of urban ecosystems and how urban ecology research progresses, each of the studies has envisioned growth and further improvement in the field and the practices that must be implemented for more sustainable development of Philippine cities. In this systematic review, recommendations from all the studies gathered were synthesized targeting different aspects of urban ecology, specifically restoration, conservation, and protection of environmental quality; improvement of the human health system in urban areas; prioritization of urban biodiversity conservation; and solutions and practices towards sustainable development. Given the fundamentals of urban ecology, encompassing various disciplines such as bio-ecological, sociological, landscape, and ecosystems approaches, the Philippine urban ecology has a potential for widening its horizon, making a holistic understanding of the discipline.

As urbanization was observed to significantly impact the environment's quality, improving or sustaining these ecosystems is vital as it affects the quality of life [153]. If urban ecosystems are not sustained, it can cause serious concerns affecting all life forms. Thus, further exploration of approaches in urban systems can result into deeper understanding on the relation of natural and socioeconomic aspects. Continuously monitoring environmental quality through evaluating risks can be a scientific basis for policymaking and implementing improvement and rehabilitation programs [111, 136]. Addressing water quality and quantity concerns and determining the effects of climate change and pollution in water bodies will also serve as the fundamental basis for a decision support system, which can be done in major water bodies in urban areas not only in Laguna De Bay and other aquatic systems in the Metropolitan Manila, but in other urban aquatic systems across the country [110, 154]. To address this, restoration and protection of waterways, such as improving wastewater treatment facilities and rehabilitation programs, can improve the water quality in urban areas [113]. As water pollution in urban areas are greatly affected by human activities, the use of hydrological modeling and geospatial analysis can also be utilized to map and trace the flow of water within urban areas and for identification of contamination hotspots and priority areas to restore. Microbiological assessments can also be conducted aside from biological assessments of macroinvertebrates, as testing the presence of water contaminants such as bacteria and viruses can greatly affect both the residents and other organisms along and within water bodies. In terms of water quality remediation, techniques such as assessing how construction of bioretention systems, and permeable pavements can aid in treatment of water pollutants.

In a human-dominated environment, one of the major concerns in terms of the urban ecosystems approach are correlated with the protection of human health and disease control. Through further studying the abiotic factors that can affect disease transmission, such as the spread of allergens, pathogens, and the ecology of vector-borne diseases, the concerned institutions can anticipate and prepare for potential outbreaks, avoiding detrimental health problems in the future [139, 155]. Pertinent control programs will also be applicable for diseases such as dengue, leptospirosis, and rabies to increase public awareness regarding the transmission and prevention of these diseases [156]. Thus, further research into urban ecosystems is crucial for thorough knowledge regarding how the environmental conditions of cities can impact public health, which in turn allowing for evidence-based policy implementation and potential urban planning looking both into the environmental quality and the safety of residents against urban-related diseases. To further improve urban environmental and health research, increasing interdisciplinary collaborations such as including medical professionals, sociologists, and decision-makers, conducting more comprehensive and long-term data collection for monitoring enables the community to address environmental justice problems ensuring that there will be equitable health for the residents of Philippine cities.

Another factor contributing to making cities beneficial for human health and well-being is the biological diversity in urban areas, giving importance to conservation measures. Merging bio-ecological and ecosystems approach can serve as an efficient method in assessing how urban biodiversity generate and support ecosystem services that benefit residents and other living organisms. However, if not conserved, it may cause destabilization of ecological communities, resulting in more detrimental effects on urban ecosystems. Maintaining vegetation is beneficial to conserving species and mitigating climate change effects such as climate amelioration, erosion control, watershed protection, and controlling the rate of carbon emissions and pollutants in the air [157]. Thus, studies have suggested strengthening the maintenance and conservation of quality habitats, developing more forest patches in the form of urban green spaces and forest parks, and further intensifying the protection of the remaining forests and their biodiversity in urban areas [34, 117, 129, 132, 158]. Biological invasion is also a prevalent concern causing further imbalances in the dynamics of species. Thus, ecological replacement can be done in order to manage invasive populations, such as replacing invasive plants with native species that can thrive in urban environments [109].

Although bio-ecological assessments have been conducted in the megacities such as the Metropolitan Manila, Cebu, Davao, further monitoring of biodiversity and the ecological factors affecting species distribution was highly recommended. Future initiatives may be composed of looking into factors such as habitat complexity, noise pollution level, spatiotemporal patterns, and determination of habitat associations, which can be done employing site observation, direct surveys, and mixed-method approaches [122, 129, 150]. Employing and strategizing novel methods for efficient and continuous monitoring and assessment of species can also help to develop an understanding of urban environment [134]. Looking into the spatial heterogeneity and patch dynamics of Philippine cities can provide insights for urban landscape approach. This includes understanding the impact of land use and land cover changes, heat indices, and landscape connectivity in relation to biodiversity can be helpful in assessing habitats that are altered by human activities [125].

In addressing the sustainable growth of cities, the involvement, knowledge, and awareness of the general public account for the majority of the progress. Thus, the human ecology based approach integrating of the population concerns, environmental education, citizen participation towards sustaining green infrastructures and spaces, and investigating management strategies have the capacity in strengthening the current knowledge on how human behaviors and organization in cities affect the urban environment [86, 151, 159, 160].

As social organizations and management plays a significant factor in sustaining urban ecosystems, delving into anthropogenic studies can supplement the gaps in binding human–environment relations. Strategic urban planning and design must be implemented by the local government units, including establishment and conservation of green spaces, ecological planning of urban and agricultural land areas, and taking into account the reduction of density of urban impervious spaces [79, 89, 123]. Increasing the adaptive capacity and resilience of urban areas, such as the production of hazardscapes and the integration of an effective solid waste management system, can also reduce the detrimental effects of climate change and natural disasters [82, 161]. Lastly, studies have also highlighted further improvement of studying the governance system in urban areas, looking into both the socio-economic and ecological well-being of cities. Such practices include strengthening the collaboration between public and private sectors, access to livelihoods opportunities and social services for the marginalized sector, enhancement of connectivity plan, residual management in industries, the establishment of monitoring offices for sustainable development, and implementation of solid policy on conservation serving as legal protection to ensure the long-term sustainable flow ecosystem services [86, 126, 150, 162].

The future of urban ecology research in the Philippines has ample potential for a better understanding of how urbanization can transform cities and all the inhabitants of these ecosystems. Through further analysis and monitoring of the interplay between social, economic, and ecological aspects, future studies will address not just the current state of Philippine cities but also what could be done to sustain a quality life in a human-dominated environment, bringing sustainable development, adaptability, and resilience into context.

4 Conclusion

In developing urban ecology in the Philippines, this paper has addressed the status and progress in the field through a systematic review of the published papers in major repositories and databases. The prevailing patterns and trends in the studies were determined and analyzed according to the publication date, themes, scope of study areas. The methodologies employed in each study were also highlighted to give attention to the current techniques used in studying urban ecosystem dynamics. Regarding the methodologies employed, looking into the varying levels of biodiversity within cities is yet to be explored, as it can serve a pivotal role in protecting urban ecosystems. Studies such as the assessment of intra-urban and urban–rural gradients, can address how species vary in terms of habitat gradients as patch areas and corridors are found to have the strongest positive impact on the biodiversity [163]. Multi-species and multi-trophic interactions in a spatiotemporal analysis can also be explored through integration of more phylogenetic, trait-based, and even remote sensing analyses to look at urban biodiversity in different perspective aside from the traditional field assessments conducted. Similar to the gaps acknowledged by Rega-Brodsky et al. [38], further studies must be conducted for a wider variety of taxonomic groups and urban ecosystems, most especially in biodiversity hotspots such as the Philippines, which can enable future researchers to go towards a multidisciplinary approach in addressing urban biodiversity.

In terms of the geographic distribution of urban ecological studies, as research studies that have been conducted were mainly conducted in metropolitan or larger cities, urban ecological knowledge regarding the smaller cities in other islands such as in Northern Luzon, Visayas, and Mindanao must also be explored. As the effects of urbanization have altered species composition and ecosystem processes, this phenomenon regarding urban ecosystems may also apply to the less populated but developing peri-urban regions in developing countries [23, 164, 165]. In progressing toward a more efficient conservation of urban ecosystems, the unfamiliarity regarding urban landscapes must first be addressed, which can be done through identifying and incorporating the distinctive elements of the urban areas to be explored [166]. Distinctive elements such as size, the overall area of green spaces, and the socioeconomic context of the region are vital considerations to fully understand and plan the conservation of ecosystem assemblages at a city-scale, which deserves more research attention as humans are considered as primary drivers of urban biodiversity [38, 167]. This can be done by looking into finer spatial extents and temporal dynamics in urban areas and comparing urban and rural composition as a multi-scale approach in landscape ecological models [55].

As urban sprawl is fueled by anthropogenic drivers, acquiring more knowledge on the root cause of ecosystem changes must also be given more research attention, as urban ecology depends on both human ecology and urban sociology. Through further studies on the social and spatial differences of cities, and the socio-economic and cultural backgrounds of the urban communities, we can look at urban systems holistically, envisioning as a single ecosystem looking into multifaceted principles in ecology and sociology [15, 60, 168]. Employing a more integrated science by means of integrating additional disciplines and quantification of targets for development, researchers can inform decision-makers and stakeholders for a better understanding of the interplay among the ecological, socio-economic, and infrastructure systems, which can advance the evolution of urban ecology research that can support the aim of the community towards more sustainable cities, conservation of urban biodiversity, and improving the residents’ quality of life [21, 28, 168]. As this systematic review have highlighted the need for further research and evidence-based action towards coping with the fast-paced urbanization in Philippine cities, giving importance to ecosystem management, sustainable planning for the mitigation of future environmental challenges, and ensuring that the coexistence of urban population and the environmental remain harmonious for future years to come is the pathway towards livable cities.