Changes in abundances of forest understorey birds on Africa's highest mountain suggest subtle effects of climate change

Impacts of anthropogenic climate change on tropical montane forests: an appraisal of the evidence

In spite of their small global area and restricted distributions, tropical montane forests (TMFs) are biodiversity hotspots and important ecosystem services providers, but are also highly vulnerable to climate change. To protect and preserve these ecosystems better, it is crucial to inform the design and implementation of conservation policies with the best available scientific evidence, and to identify knowledge gaps and future research needs. We conducted a systematic review and an appraisal of evidence quality to assess the impacts of climate change on TMFs. We identified several skews and shortcomings. Experimental study designs with controls and long-term (≥10 years) data sets provide the most reliable evidence, but were rare and gave an incomplete understanding of climate change impacts on TMFs. Most studies were based on predictive modelling approaches, short-term (<10 years) and cross-sectional study designs. Although these methods provide moderate to circumstantial evidence, they can advance our understanding on climate change effects. Current evidence suggests that increasing temperatures and rising cloud levels have caused distributional shifts (mainly upslope) of montane biota, leading to alterations in biodiversity and ecological functions. Neotropical TMFs were the best studied, thus the knowledge derived there can serve as a proxy for climate change responses in under-studied regions elsewhere. Most studies focused on vascular plants, birds, amphibians and insects, with other taxonomic groups poorly represented. Most ecological studies were conducted at species or community levels, with a marked paucity of genetic studies, limiting understanding of the adaptive capacity of TMF biota. We thus highlight the long-term need to widen the methodological, thematic and geographical scope of studies on TMFs under climate change to address these uncertainties. In the short term, however, in-depth research in well-studied regions and advances in computer modelling approaches offer the most reliable sources of information for expeditious conservation action for these threatened forests.

Physiologically vulnerable or resilient? Tropical birds, global warming, and redistributions

Tropical species are considered to be more threatened by climate change than those of other world regions. This increased sensitivity to warming is thought to stem from the assumptions of low physiological capacity to withstand temperature fluctuations and already living near their limits of heat tolerance under current climatic conditions. For birds, despite thorough documentation of community-level rearrangements, such as biotic attrition and elevational shifts, there is no consistent evidence of direct physiological sensitivity to warming. In this review, we provide an integrative outlook into the physiological response of tropical birds to thermal variation and their capacity to cope with warming. In short, evidence from the literature suggests that the assumed physiological sensitivity to warming attributed to tropical biotas does not seem to be a fundamental characteristic of tropical birds. Tropical birds do possess the physiological capacities to deal with fluctuating temperatures, including high-elevation species, and are prepared to withstand elevated levels of heat, even those living in hot and arid environments. However, there are still many unaddressed points that hinder a more complete understanding of the response of tropical birds to warming, such as cooling capacities when exposed to combined gradients of heat and humidity, the response of montane species to heat, and thermoregulation under increased levels of microclimatic stress in disturbed ecosystems. Further research into how populations and species from different ecological contexts handle warming will increase our understanding of current and future community rearrangements in tropical birds.

Diversity and relative abundance of bird species in the two habitat types of Dokima forest Awi zone, Ethiopia

Birds are the most widespread vertebrate group, as they can be found in practically every type of habitat. However, lack of knowledge on bird ecology in Afrotropical highlands and bird habitat degradation are the main problems that is why this research was studied. The study was conducted in Awi zone, Amhara National Regional State with the objective of the diversity and relative abundance of bird species in the two habitat types of Dokima forest in Awi zone, Ethiopia. Between November 2018 and December 2020, the transect method was conducted in both dry and wet seasons. Using one-way ANOVA, the effect of seasons and habitats on species richness and abundance was investigated and compared. In both the dry and wet seasons, a total of 2233 individuals, 47 species belonging to 35 families, and 14 orders were recorded. The abundance of bird species was not statistically differed between habitat types in the dry season, but it was statistically significantly in the wet season. The mean abundance of bird species differed significantly between the dry and wet seasons. In the dry season, the forest habitat type had the highest species diversity index (H' = 3.18) and the highest evenness (J = 0.94), while in the wet season, the forest habitat type had the highest evenness (J = 0.94). These habitats must be conserved in order to protect the birds that live in the area.

Diversity and relative abundance of bird species in the two habitat types of Dokima forest Awi zone, Ethiopia

Birds are the most widespread vertebrate group, as they can be found in practically every type of habitat. However, lack of knowledge on bird ecology in Afrotropical highlands and bird habitat degradation are the main problems that is why this research was studied. The study was conducted in Awi zone, Amhara National Regional State with the objective of the diversity and relative abundance of bird species in the two habitat types of Dokima forest in Awi zone, Ethiopia. Between November 2018 and December 2020, the transect method was conducted in both dry and wet seasons. Using one-way ANOVA, the effect of seasons and habitats on species richness and abundance was investigated and compared. In both the dry and wet seasons, a total of 2233 individuals, 47 species belonging to 35 families, and 14 orders were recorded. The abundance of bird species was not statistically differed between habitat types in the dry season, but it was statistically significantly in the wet season. The mean abundance of bird species differed significantly between the dry and wet seasons. In the dry season, the forest habitat type had the highest species diversity index (H’ = 3.18) and the highest evenness (J = 0.94), while in the wet season, the forest habitat type had the highest evenness (J = 0.94). These habitats must be conserved in order to protect the birds that live in the area.

Seasonal Changes in an Afromontane Forest Bird Community in Tanzania

Seasonal variation in the composition of avian communities is poorly documented in African montane forests. Using field observations, mist-netting data (63,424 NMH), recording of mixed-species flocks (160 flocks noted), and of the feeding ecology of greenbuls (757 observations), we document marked seasonal changes in a bird community in an East African montane forest (1,340–2,130 m) in the Udzungwa Mountains in south-central Tanzania. This mountain range contains the largest remaining forests in the Eastern Arc Mountains in Tanzania, part of a key global biodiversity hotspot. Our analysis is based on data in the dry and wet season from about 12 months of fieldwork. Field observation data combined with mist-net data demonstrate noticeable seasonal changes in certain species’ abundances, indicating (i) seasonal movements out of the montane forest during the dry season and (ii) movements of part of the populations for other species. Our mist-net results show a significant difference in species abundances between the two seasons driven by 16 species. We also document significant changes in diet for two species of greenbuls, which shift feeding behavior from arthropods in the wet season to include a larger proportion of fruit in their dry season diet. Our results further show that birds are more active in mixed-species flocks in the dry season, with a significantly higher average number of species and of individuals in the dry season, i.e., 11.3 (±0.52 SE) species, 32.3 (±1.76 SE) individuals] compared to the wet season 9.7 (±0.78 SE) species, 20.8 (±1.85 SE) individuals]. One of two very distinctive types of mixed-species flocks – confined to the understory – exists only in the dry season. We discuss these changes to seasonal variability in climate, i.e., temperature and precipitation.

Improvements in reports of species redistribution under climate change are required

Studies have documented climate change-induced shifts in species distributions but uncertainties associated with data and methods are typically unexplored. We reviewed 240 reports of climate-related species-range shifts and classified them based on three criteria. We ask whether observed distributional shifts are compared against random expectations, whether multicausal factors are examined on equal footing, and whether studies provide sufficient documentation to enable replication. We found that only ~12.1% of studies compare distributional shifts across multiple directions, ~1.6% distinguish observed patterns from random expectations, and ~19.66% examine multicausal factors. Last, ~75.5% of studies report sufficient data and results to allow replication. We show that despite gradual improvements over time, there is scope for raising standards in data and methods within reports of climate-change induced shifts in species distribution. Accurate reporting is important because policy responses depend on them. Flawed assessments can fuel criticism and divert scarce resources for biodiversity to competing priorities.

Afrotropical montane birds experience upslope shifts and range contractions along a fragmented elevational gradient in response to global warming

Global warming is predicted to result in upslope shifts in the elevational ranges of bird species in montane habitats. Yet few studies have examined changes over time in the elevational distribution of species along fragmented gradients in response to global warming. Here, we report on a resurvey of an understory bird community in the Usambara Mountains in Tanzania, along a forested elevational gradient that has been fragmented over the last 200 years. In 2019, we resurveyed seven sites, ranging in elevation from 360 m to 2110 m, that were originally surveyed between 1979 and 1981. We calculated differences in mean elevation and lower and upper range limits for 29 species between the two time periods and corrected for possible differences in elevation due to chance. Over four decades, we documented a significant mean upslope shift across species of 93 m. This shift was smaller than the 125 m expected shift due to local climate warming. Of the 29 focal species, 19 shifted upslope, eight downslope, and two remained unchanged. Mean upslope shifts in species were driven largely by contracting lower range limits which moved significantly upslope on average across species by 183 m, while upper range limits shifted non-significantly upslope by 72 m, leading to a mean range contraction of 114 m across species. Community composition of understory bird species also shifted over time, with current communities resembling communities found historically at lower elevations. Past forest fragmentation in combination with the limited gap-crossing ability of many tropical understory bird species are very likely important contributory factors to the observed asymmetrical shifts in lower and upper elevational range limits. Re-establishing forested linkages among the largest and closest forest fragments in the Eastern Arc Mountains are critical to permitting species to shift upslope and to reduce further elevational range contractions over time.

Climate Change in the Tropics: Ecological and Evolutionary Responses at Low Latitudes

Climate change is affecting every ecosystem on Earth. Though climate change is global in scope, literature reviews on the biotic impacts of climate change have focused on temperate and polar regions. Tropical species have distinct life histories and physiologies, and ecological communities are assembled differently across latitude. Thus, tropical species and communities may exhibit different responses to climate change compared with those in temperate and polar regions. What are the fingerprints of climate change in the tropics? This review summarizes the current state of knowledge on impacts of climate change in tropical regions and discusses research priorities to better understand the ways in which species and ecological communities are responding to climate change in the most biodiverse places on Earth.

Cross-taxa generalities in the relationship between population abundance and ambient temperatures

Identifying patterns in the effects of temperature on species' population abundances could help develop a general framework for predicting the consequences of climate change across different communities and realms. We used long-term population time series data from terrestrial, freshwater, and marine species communities within central Europe to compare the effects of temperature on abundance across a broad range of taxonomic groups. We asked whether there was an average relationship between temperatures in different seasons and annual abundances of species in a community, and whether species attributes (temperature range of distribution, range size, habitat breadth, dispersal ability, body size, and lifespan) explained interspecific variation in the relationship between temperature and abundance. We found that, on average, warmer winter temperatures were associated with greater abundances in terrestrial communities (ground beetles, spiders, and birds) but not always in aquatic communities (freshwater and marine invertebrates and fish). The abundances of species with large geographical ranges, larger body sizes, and longer lifespans tended to be less related to temperature. Our results suggest that climate change may have, in general, positive effects on species' abundances within many terrestrial communities in central Europe while the effects are less predictable in aquatic communities.

Factors governing the prevalence and richness of avian haemosporidian communities within and between temperate mountains

Mountains are well-suited systems to disentangle the factors driving distribution of parasites due to their heterogeneity of climatic and habitat conditions. However, the information about the relative importance of environmental factors governing the distribution of avian haemosporidians on temperate mountains is very limited. The main goal of the present study is to identify the factors determining prevalence and richness in avian haemosporidians (Plasmodium, Haemoproteus and Leucocytozoon) at the community level along elevational gradients on two mountain ranges located around the northern and southern limits of the Iberian Peninsula (Spain). We used samples from 68 avian species and 1,460 breeding individuals caught over widespread woodland and open habitats. Our findings confirmed the importance of climatic variables explaining prevalence and richness on Iberian mountains. However, landscape variables and other factors named host richness and migration behaviour explained more variation than climatic ones. Plasmodium genus preferred open and warm habitats. Water sources were also important for the southern but not for the northern mountain. Haemoproteus and Leucocytozoon showed affinities for woodland areas. Climatic conditions for Haemoproteus and Leucocytozoon were dependent on the mountain range suggesting some adaptation of avian haemosporidian and their invertebrate vectors to the climatic particularities of both mountain massifs. In contrast to Plasmodium and Haemoproteus genera, Leucocytozoon prevalence and richness values were significantly higher in the southern mountain range. Overall, our findings at the community level has enriched the relative weight and effect direction of environmental factors governing the distribution and prevalence of the avian haemosporidian community. Also, our results provide a caution message about the precision of predictive models on parasite distributions based on climatic variables, since such predictions could overestimate the effect of climate change scenarios on the transmission of the haemosporidians.