It’s early June, and the time of year when the natural world is in full swing. Flowering plants are in bloom, and a profusion of insects, birds, and mammals have hatched, woken from their winter hibernations, or migrated back from shores afar.
Scientific understanding of these natural rhythms has changed greatly over the course of human history. The sixteenth century textbook, History and Nature of the Northern Peoples by Swedish Archbishop Olaus Magnus, reported that swallows hibernate at the bottom of lakes over winter.
Today things have improved somewhat, and we have an excellent understanding of how many species seasonally migrate between countries, continents, rivers and oceans – although many mysteries remain. For example, where great white sharks raise their young or how successive generations of monarch butterflies navigate between North America in summer and Mexico in winter remains elusive to science.
Over time our increasing knowledge of the natural world has given us an ever-increasing wealth of data to understand how species populations fluctuate. Unfortunately, much of this data makes for quite depressing reading. For example, the UK butterfly population data starts in 1976, and demonstrates an overall 50% decline since then. A recent, much publicised, study in Germany demonstrated a 73% decline in insect biomass between 1989-2016.
However, it is fair to say that these datasets and studies don’t stretch back far enough to understand the full impact of human activities on species distribution and abundance. The population of species in pre-industrial times will forever be a mystery, although we can piece together information from a variety of sources, for example:
“Insects of all kinds literally swarmed. Butterflies were in profusion. The silver washed fritillary was in hoards… they were so common that the sun touched their overnight resting places, they dropped out the trees like an autumnal showering of leaves.” – Frederick William Froehawk (1880)
The silver washed fritillary is now a relatively rare butterfly in the UK and numbers in this magnitude have not been experienced in living memory. Another more recent example can be seen by looking at sport fishing catches in Florida since the 1950s:
This presents us with a problem. To accurately assess the health of a particular population you need to understand what a healthy population looks like. However, by and large, the majority of the datasets we have, and habitats we have studied, are already degraded.
The line in the sand that we use as a reference point for understanding what impacts we have is called the baseline. Clearly, in the case of the silver washed fritillary, and sea fish population in Florida, baseline populations have changed significantly. Any study which was to use 2020 as a baseline would be very different to one which referenced 1880 or 1950 (if that was possible).
This concept is called a shifting baseline and raises the question that we are likely to be vastly underestimating what “normal” looks like and how many species have declined.
Shifting baselines is a key concept in conservation and highlights the need for all of us to make decisions which halt biodiversity decline, and do what we can to help nature recover.
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