Overview

This study by J.M. Reed and colleagues, published in Urban Ecosystems, explores how urban development influences the presence and abundance of two amphibian species: the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica). Both species rely on temporary woodland pools, known as vernal pools, for breeding. Because amphibians are highly sensitive to environmental changes, they serve as indicators of ecosystem health. The researchers aimed to determine how surrounding land cover, such as forest area, impervious surfaces, and road proximity, affects amphibian occurrence and breeding success in human-altered landscapes.

Methods

Reed and his team surveyed 41 vernal pools in central Massachusetts that represented a range of surrounding land uses, from heavily forested to highly urbanized areas. They measured egg mass counts to estimate breeding abundance and recorded environmental factors including forest cover within 100–300 meters, hydroperiod, road density, and impervious surface area. To evaluate which factors most influenced amphibian presence, the researchers used logistic regression and stepwise model selection.

A key strength of the study was its use of GIS data to quantify the surrounding landscape, offering more precision than visual observation alone. However, one limitation was that data collection occurred during a single breeding season. The authors noted that year-to-year differences in rainfall and hydroperiod could influence amphibian breeding success, meaning a longer-term study might reveal additional trends or variability.

Results

The study found a clear negative relationship between urbanization and amphibian presence. Spotted salamanders were observed in 69 percent of pools with over 75 percent surrounding forest, but in fewer than 20 percent of pools where forest cover was below 25 percent. Wood frogs showed a similar pattern, though they appeared somewhat more tolerant of moderate development.

Road density within 100 meters of pools was one of the most consistent predictors of absence. Roads not only fragment habitats but also increase adult mortality as salamanders and frogs migrate to breeding sites. In addition, the amount of impervious surface near pools was strongly linked to lower abundance, likely due to disrupted hydrology and reduced water quality. The authors pointed out that even small increases in pavement or built infrastructure can lead to disproportionate ecological effects, illustrating how sensitive amphibians are to habitat loss and fragmentation.

Reflection / Critique

This study presents convincing evidence that urbanization substantially reduces amphibian populations, but there are several aspects that could have been expanded upon. While the authors recommend maintaining at least 30 to 50 meters of forest buffer around vernal pools, they do not provide practical guidance on how these recommendations might be implemented through zoning or conservation policy. Including examples of towns or municipalities that have successfully integrated amphibian habitat protection into land-use planning would have made the research more applied and actionable.

Another limitation is the lack of direct water quality data. The authors mention that pollution from runoff could influence amphibian populations, but they did not measure chemical variables such as nitrogen, phosphorus, or heavy metals. Without this information, it remains uncertain whether declines were driven primarily by habitat fragmentation or by contamination of breeding pools. Future studies combining both land-use and water chemistry analyses could paint a fuller picture of how urbanization impacts amphibians.

Even with these limitations, the study makes a valuable contribution to urban ecology. The finding that spotted salamanders virtually disappear when impervious cover exceeds 25 to 30 percent provides an important threshold for conservation planning. The authors also highlight how both landscape connectivity and small-scale features like forest buffers can make a major difference in sustaining amphibian populations.

Overall, this research offers a strong reminder that sustainable development must consider the needs of species that rely on small, seasonal, and easily overlooked habitats. Amphibians like the wood frog and spotted salamander are not just victims of habitat loss but also indicators of how human choices shape the health of entire ecosystems.

Reference:
Reed, J. M., et al. (2005). Urbanization Effects on Spotted Salamander and Wood Frog Presence and Abundance. Urban Ecosystems

Overview

This study, published in Urban Forestry & Urban Greening (2023), looks at how non-native plants and “illegitimate” pollination behaviors affect hummingbird activity in urban environments. Urbanization often replaces native plants with non-native ones, which can change pollinator behavior and plant-animal interactions. The researchers wanted to figure out whether these non-native species still help sustain hummingbirds in cities, even when the birds aren’t directly pollinating the flowers.

Methods

The researchers surveyed urban landscapes to record the diversity of flowering plants and the frequency of hummingbird visits. They differentiated between legitimate interactions, where pollination could occur, and illegitimate ones, where hummingbirds accessed nectar without pollinating. Sites with varying proportions of native and non-native species were compared to determine how plant origin influenced hummingbird foraging behavior. The study also monitored flowering duration to evaluate how non-native plants extended nectar availability throughout the year.

Results

The findings revealed that non-native plants played a substantial role in sustaining urban hummingbird populations. These species often bloomed outside the flowering periods of native plants, effectively bridging resource gaps. Interestingly, even illegitimate visits still contributed to maintaining hummingbird presence, indicating that access to nectar, regardless of pollination success, supports pollinator persistence in cities. The study emphasized that plant diversity, rather than strict nativity, can strengthen urban ecological networks.

Reflection / Critique

I thought this was a really interesting study because it challenges the assumption that only native plants are valuable for supporting wildlife. The authors made a strong case for recognizing the role of non-native plants in maintaining biodiversity in cities, especially for specialized pollinators like hummingbirds. However, I wish they had gone into more detail about how these non-native plants might affect other pollinators or long-term ecosystem stability. It also would’ve been helpful if they compared data from different cities or regions to make their conclusions more generalizable. Overall, the paper was well done and brought up a thought-provoking point, that even “imperfect” ecological interactions can still have real value in human-dominated environments.

Urban Forestry & Urban Greening (2023). Non-native plants and illegitimate interactions are highly relevant for supporting hummingbird pollinators in the urban environment. https://www.sciencedirect.com/science/article/abs/pii/S1618866723001966

Overview

The article that I am reviewing is “Bat Activity in an Urban Landscape: Patterns at the Landscape and Microhabitat Scale” by Gehrt and Chelsvig (2003). This study addresses an important and often overlooked question in urban ecology: how do bats respond to increasing urbanization, and to what extent do both large-scale (landscape-level) and fine-scale (microhabitat) features influence their activity? Bats play a crucial ecological role as insect predators, yet research on their persistence in urban and suburban environments has historically lagged behind studies of more visible species.

The authors sought to answer two primary questions. First, they inquired about how landscape-scale variables, such as the proportion of forest cover or urban development, influence overall bat activity. Second, they examined whether microhabitat characteristics, including canopy cover, presence of water, and local vegetation structure, explain additional variation in bat activity beyond what can be predicted by landscape context alone. Together, these questions aimed to shed light on how bats navigate increasingly fragmented urban environments and what habitat elements are most critical for their persistence.

Methods

To investigate these questions, the researchers conducted acoustic surveys across multiple sites representing a gradient of urbanization. Ultrasonic bat detectors were used to record echolocation calls, which served as an index of bat activity. The study design incorporated two spatial scales of analysis. At the landscape scale, the researchers quantified features such as forest cover, urban development, and impervious surface area surrounding each site. At the microhabitat scale, they measured local site variables including canopy density, vegetation structure, and proximity to water.

Data collection took place during the summer months to coincide with peak bat activity. The researchers then analyzed bat “passes” (recorded calls) to determine how strongly activity correlated with both landscape and microhabitat variables, allowing them to separate broad-scale effects from those operating at the site level.

Results

The results revealed a clear pattern: bat activity declined as the amount of urban cover increased and was positively associated with forest cover. This suggests that bats are sensitive to habitat loss and fragmentation at the landscape level. However, the study also found that microhabitat features significantly influenced bat activity even within similarly urbanized areas. Sites with dense tree canopy, well-developed vegetation structure, and water sources exhibited higher activity than sites lacking these features.

These findings demonstrate that landscape context and local habitat quality interact to shape bat distributions. Two sites with comparable levels of urbanization could display markedly different levels of bat activity depending on their microhabitat composition. This means that conserving or restoring key habitat elements at the local scale can have a meaningful impact on maintaining bat populations even within urban settings.

Critiques and Reflection

This study is commendable for highlighting that both large-scale and fine-scale habitat features must be considered when developing urban wildlife management strategies. Its reliance on acoustic monitoring was also useful, as it provided a non-invasive yet comprehensive method for assessing bat presence and activity across numerous sites. Furthermore, the study’s findings carry clear implications for urban planning, suggesting that preserving forest patches, maintaining tree canopy, and protecting water bodies can promote bat activity in otherwise developed landscapes.

Nevertheless, there are areas in which the study could be strengthened. The analysis aggregates overall bat activity rather than distinguishing among species or foraging guilds, which may obscure species-specific responses to urbanization. Some species may be more tolerant of urban settings than others, and identifying these differences would help refine conservation priorities. Additionally, the study’s temporal scope is limited; sampling across multiple seasons or under varied environmental conditions could reveal whether the observed patterns are consistent year-round. Finally, the article could have offered explicit management recommendations, such as quantifiable targets for canopy cover or patch size, that would be useful for city planners and conservation practitioners.

Despite these limitations, the study contributes meaningfully to urban ecology by illustrating that microhabitat improvements can mitigate some of the negative effects of urbanization on bats. It challenges the notion that urban areas are inherently unsuitable for wildlife and underscores the importance of intentional habitat design in cities.

Reference

Gehrt, S.D. and Chelsvig, J.E. (2003), BAT ACTIVITY IN AN URBAN LANDSCAPE: PATTERNS AT THE LANDSCAPE AND MICROHABITAT SCALE. Ecological Applications, 13: 939-950. https://doi.org/10.1890/02-5188