The Paardeberg stands out as a mountainous island in an agricultural landscape between Paarl/Wellington and Malmesbury in the Swartland region of the Western Cape. Very little bird ringing has taken place here, so Les Underhill and I had a ringing session on Bowwood Farm on Wednesday.
The top species was Cape White-eye (n=22), followed by Southern Masked Weavers (n=8), where 2 of the latter were males in partial breeding plumage. The ring of one bird has been recovered in the Paardeberg area, a Cape Weaver ringed with ring 231054 in Tygerberg.
Thanks to Julian and Bridget Johnsen for hosting us!
In this week’s digest of research that caught our attention, we look at socio-economic and development issues associated with background climate oscillations and anthropogenic-driven climate change. We also look at climate change mitigation and biodiversity conservation, artificial selection pressures on a large carnivore, and methods of estimating population density in an elusive carnivore species.
Bet the farm – rolling the climate dice
Food security around the world is closely linked to climate variability, but in a recent article in Nature Communications we learn just how extensive the problem is. Crop productivity on two-thirds of the world’s cropland is significantly affected by three climate oscillations: El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the North Atlantic Oscillation (NAO). The areas affected by the three oscillations are inhabited by approximately 4 billion people and contribute two-thirds of global food crop calorie production.
Ed: Against this background, the implications of adding variability and unpredictability of anthropogenic-driven climate change would suggest that risk in crop farming and food security will only increase for half the world’s population.
The carbon sins of the rich shall be visited upon the poor
The world’s population is becoming increasingly urban, and recent rapid urbanisation has resulted in a proliferation of informal urban settlements or slums, which are home to > 800 million people. Some of this urban migration may be due to food security risk associated with climate variability (such as described in the article above). A compelling article in Ecological Indicators provides an important example of the social science required for assessing climate change vulnerability in these at-risk urban communities. In the particular slum community studied, overall vulnerability to climate change was high, there was a high information barrier (and hence low awareness of climate change impacts). As might be expected, for coping strategies, financial and food support were deemed important, followed by information support.
Ed: Interestingly, technological support was deemed least important for coping with climate change in slum communities, yet much attention is focused on technological interventions and relatively little attention is given to practical information and resource distribution.
Picking winners and losers – conserving carbon or biodiversity
Although the net impact of climate change is likely to be negative for biodiversity, there will be some taxonomic groups that benefit from climate change. Carbon conservation – specifically, conserving above-ground carbon stocks in tropical forests – is seen as one of the ways to combat climate change. Contrary to the putative net effects of climate change, it is tacitly assumed that this form of carbon conservation will promote biodiversity. A thought-provoking article in Science Advances suggests that the relationship between above-ground carbon stocks and biodiversity differs for different taxonomic groups, and may also differ in re-growth forests compared to old growth forests (within a taxonomic group). Thus, among the taxonomic groups studied, the relationship between carbon stocks and biodiversity could vary from positive to negative and could appear linear or non-linear. Choosing a single climate change mitigation strategy, such as conserving tropical forests to maximise carbon stocks, will inherently include trade-offs in biodiversity in certain taxonomic groups. A similar article in Science Advances from 2017 about using fire suppression in savannas to maximise carbon sequestration came to similar conclusions. Thus, more nuanced, integrated approaches that consider both carbon conservation and biodiversity conservation (across multiple taxonomic groups) may be required as we try to mitigate anthropogenic-driven climate change.
Ed: This is going to be a tricky concept to grapple with. Climate change in general is leading to population declines, geographic range shifts (and expansions or contractions). When biodiversity is already a climate change concern, how will we weigh the biodiversity benefits of mitigating climate change against the potential biodiversity costs (in some taxa) of maximising carbon conservation? As a species, we will need to become much better at assessing risks, attributing value, and optimising trade-offs.
Survival of the … slowest?
Typically, in harvested populations, the selection pressure of hunting or harvest should select for accelerated life history traits. However, research on a hunted population of brown bears in Sweden, published this week in Nature Communications, shows that when hunting regulations prevent the harvest of mothers with cubs, selection pressure may favour slower life history traits. Mothers that exhibit longer maternal care receive a survival benefit. Interestingly, this survival benefit cancels out the loss of reproductive opportunities associated with the slower breeding strategy, such that net fitness for the slower breeding females is similar to that of females following a “normal” maternal care strategy. Over the last 30 years, the proportion of litters in the population raised over 2.5 years has increased measurably relative to the proportion of litters raised over 1.5 years.
Ed: A great demonstration of artificial selection at work … and over a relatively short time-frame for a long-lived large mammal.
Leopards are contagious too,
Be careful tiny tots,
They don’t give you a temperature
But lots and lots of spots
Spotty spotting of the spotted
A major issue in biodiversity research revolves around how to count animals in a population or estimate their population density reliably. This is particularly problematic for “cryptic” species that have low detection probabilities. Solitary felids often fit into this category, including leopards (Panthera pardus), which are largely nocturnal and have coat patterns that provide good camouflage. In a great study reported in the African Journal of Ecology, leopard density was estimated across a broad geographic region in South Africa (the Eastern Cape Province and Western Cape Province). The authors used movement data of collared animals and “captures” from remotely-triggered cameras to estimate density using two different techniques – which provided surprisingly similar final density estimates. These density estimates of approximately 1 leopard per 100 sq km are low compared to published estimates for populations elsewhere in the leopard’s geographic range (published, for example, here). Even within this region, density estimates varied greatly among sites (from 0.24 to 1.89 leopards per 100 sq km).
Ed: This study produced great congruence between two different methods of estimating leopard density, suggesting that the reported densities for the region are quite reliable. The study also opens up interesting questions about what drives variability in leopard population density (both within this geographic region, and across the leopard’s geographic range).
I can’t believe it’s not butter!
This week’s conservation art profile:
Malachite Kingfisher (oil painting … not a photo!) by Tanya Scott.
Tanya has recently completed an MSc at the University of Cape Town using the data from the bird atlas project in South Africa (Birds along a transect across KwaZulu-Natal: altitudinal preference and altitudinal migration). She represented South Africa in the half-marathon at the 29th Summer Universiade in Taipei City in 2017. Her last formal art education was at Westerford High School in Cape Town where the art teacher was Mr Anthony Cain.
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