Biology subjects

Johnson, T. F.

Publications and source records attributed to Johnson, T. F..

8 recordsLinked to original sources

bioRxiv2026

Vertebrates do not display consistent declines in abundance or stability with contemporary range or realized climate niche centrality

The abundant-centre (ACH) and stable-centre hypotheses (SCH) predict population abundance and stability decline with increasing distances from a species' range and multivariate climate niche centres. ACH and SCH are widely held assumptions underpinning many ecological and conservation applications, with range and climate centrality often assumed to reflect suitability. However, empirical support that abundance (distance-abundance) and stability (distance-variability) decline away from range and climate centres is mixed and hampered by radically different climate centrality assumptions. Here, we test distance-abundance relationships in >5000 vertebrate species and distance-variability relationships in >1000 vertebrate species across their realized geographic and climate niche spaces. We found no vertebrate taxa display consistent declines in abundance or stability with increasing distances from range centres or realized climate (niche) centres modelled from species' breeding ranges, native ranges or contemporary occurrences. Distance-abundance and distance-variability relationships were weak and inconsistent across taxa irrespective of centrality metric, modelling approach, climate variables, abundance metric or dataset. Contemporary vertebrate abundance patterns, therefore, are often decoupled from position in contemporary range and realized climate space, challenging a central assumption of core-periphery models. Broadly, our study indicates that frequently used range and climate centrality metrics may be weak predictors of vertebrate abundance patterns in contemporary landscapes and biological forecasting or climate change applications should be cautious of their unvalidated use.

ecology↗

bioRxiv2025

Reintroductions backfire by destabilising food webs and triggering further extinction cascades

Conservation interventions like reintroduction are considered vital to bending the curve of biodiversity loss1, with the potential for multiplicative benefits that not only reduce extinction pressure on the reintroduced species, but also restore wider community dynamics and ecosystem functions2,3. Its growing popularity reflects these perceived benefits4. Reintroduction success is usually judged only by the survival of the released species4, but there is no guarantee that the wider community will recover. Using simulated food webs, we show that reintroductions can frequently have unintended negative consequences: triggering extinction cascades, reducing biomass, and destabilising communities. These perverse impacts are unlikely to be detected as reintroduction success is often measured solely by the ability for reintroduced species to survive - which our models suggest is likely - introducing a risk that conservation action superficially appears successful but is actually further depleting our ecosystems.

ecology↗

bioRxiv2025

Halting predicted vertebrate declines requires tackling multiple drivers of biodiversity loss

Anthropogenic threats are reshaping Earths biodiversity at an unprecedented rate and scale1-3. Conservation policies often prioritise threats like habitat loss and exploitation based on their global prevalence. However, these assessments rarely quantify the impacts of individual or interacting threats, potential masking the true effects of the Anthropocene4-6. Here, we quantitatively analyse the trends of 3,129 vertebrate populations worldwide with documented exposure to specific and multiple threats. Populations impacted solely by habitat loss or exploitation, the most prevalent threats, do not show the fastest declines. Rather, populations exposed to disease, invasive species, pollution, and climate change decline more rapidly. However, habitat loss and exploitation - along with climate change - do act as additive interactive threats, amplifying population declines. Notably, these interactive threats contribute to population declines, more than temporal or spatial sources of variation. Finally, counterfactual scenarios show that to achieve global non-negative vertebrate population trends, we need to mitigate the effects of multiple threats. These findings underscore the urgency of addressing the compounding effects of multiple threats to halt biodiversity loss and suggest that the local-scale impacts of climate change may be more severe than previously recognized.

ecology↗

bioRxiv2024

Response diversity is a major driver of temporal stability in complex food webs

Global change constitutes a major threat to biodiversity and ecosystem functioning which can materialise in the temporal stability of ecological communities. However, the majority of research on stability has focused on single trophic level communities and has not yet integrated classic theory about species richness and food web structure with more recent theory centred on response diversity and stochasticity. Using a stochastic, bioenergenetic food web model, we integrate these multiple bodies of theory to reveal that response diversity is a major driver of community stability. Moreover, our integrated theory reveals that positive stability-richness relationships emerge only in the presence of response diversity. In contrast to previous work, food web structure is only a secondary driver of community stability, but interacts with response diversity to determine the sign of the stability-richness relationship. Our study reveals identifiable pathways by which food web structure and response diversity drive community stability, and raises concerns about how the loss of response diversity (biotic homogenisation) may lead to a breakdown of community stability.

ecology↗

bioRxiv2022

Overconfidence undermines global wildlife abundance trends

In the face of rapid global change and an uncertain fate for biodiversity, it is vital to quantify trends in wild populations. These trends are typically estimated from abundance time series for suites of species across large geographic and temporal scales. Such data implicitly contain phylogenetic, spatial, and temporal structure which, if not properly accounted for, may obscure the true magnitude and direction of biodiversity change. Here, using a novel statistical framework to simultaneously account for all three of these structures, we show that the majority of current abundance trends estimates among 10 high-profile datasets, representing millions of abundance observations, are likely unreliable or incorrect. Our new approach suggests that previous models are too simplistic, incorrectly estimating global abundance trends and often dramatically underestimating uncertainty, an aspect that is critical when translating global assessments into policy outcomes. Further, our approach also results in substantial improvements in abundance forecasting accuracy. Whilst our results do not improve the outlook for biodiversity, our framework does allow us to make more robust estimates of global wildlife abundance trends, which is critical for developing policy to protect our biosphere.

ecology↗

bioRxiv2022

CaPTrends: A global database of Carnivoran Population Trends

MotivationPopulation trend information is an Essential Biodiversity Variable for monitoring change in biodiversity over time. Here, we present a global dataset of 1122 population trends describing changes in abundance over time in large mammals from the Order Carnivora - some of the worlds most charismatic and functionally important fauna. Main types of variables includedKey data fields for each record: species, coordinates, trend timeframe, methods of data collection and analysis, and population timeseries or summarised trend value. Population trend values are reported using quantitative metrics in 75% of records that collectively represent more than 6500 population estimates. The remaining records qualitatively describe population change (e.g. increase). Spatial location and grainRecords represent locations across the globe (latitude: -51.0 to 80.0; longitude: -166.0 to 166.0) with more trends found within the northern temperate zone. Time period and grainRecords span from 1726 to 2017, with 92% of trends starting after 1950. Major taxa and level of measurementWe conducted a semi-systematic search for population trend data in 87 species from four families in the order Carnivora: Canidae, Felidae, Hyaenidae and Ursidae. We compiled data for 50 of the 87 species. Software format.csv

ecology↗

bioRxiv2021

Socioeconomics drive population change in the world's largest carnivores

Land-use1,2 and climate change3-5 have been linked to wildlife population declines, but the role of socioeconomic factors in driving declines, and promoting population recoveries, remains relatively unexplored despite its likely importance. Here, we evaluate a comprehensive array of potential drivers of population changes observed in some of the worlds most charismatic species - large mammalian carnivores. Our results reveal a strong role of human socioeconomic development, which we find has a greater impact on population change than habitat loss and climate change. Increases in socioeconomic development are linked to sharp population declines but, importantly, once development is high, carnivore populations have the potential to recover. These links between human development and wildlife population health highlight the challenges ahead to achieve the different UN Sustainable development goals.

ecology↗

bioRxiv2021

Density of Pied Crows Corvus albus in two of South Africa's protected areas

In recent decades, the pied crow Corvus albus population has grown in southern Africa, and this may have had impacts on other species. Conservationists and land managers may question the degree of threat posed by pied crows to other species, but a scarcity of ecological information on pied crows limits evidence-based decision-making. Using a distance density function we provide initial pied crow density estimates of 0.24 crows km-2 (0.12-0.5; 95% CI) and 0.18 crows km-2 (0.07-0.45; 95% CI) in two protected areas in the Northern Cape Province of South Africa. We infer that pied crow density is negatively associated with the normalised difference vegetation index (NVDI).

ecology↗