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Skip to 0 minutes and 4 seconds Populations are groups of organisms of the same species living in the same area at the same time. Population biology uses concepts from ecology, evolution, genetics and a bit of maths to investigate the reproduction, development, distribution and survival of an organism. It’s intrinsically interesting to understand why I might see ospreys in Scotland and red kites in Yorkshire, or to understand why salmon lay hundreds of eggs, yet a blue tit in your garden only lays a dozen? As biologists we look to understand species biology for its value in this sense alone.

Skip to 0 minutes and 35 seconds At the moment though, with the human population having doubled in the space of 50 years, and the UN estimating that 1 million species are at risk of extinction, we can use our knowledge of population biology to have a real positive impact on the world around us. We can understand how populations are changing over time and scientific research can influence policy decisions, be used to develop management and conservation strategies, or to limit the spread of invasive species. Populations can be described by their size, density and growth. With unlimited resources populations can grow exponentially, but as resources become limited this growth rate slows and eventually stops at the population’s carrying capacity.

Skip to 1 minute and 14 seconds The size that a population reaches depend on a number of factors such as competition for food, nesting sites, or the presence of disease or predators. The individuals in a population can compete with other individuals of the same species in intraspecific competition, or with other species via interspecific competition. One example of interspecific competition that we see in the UK is between red squirrels and grey squirrels. Red squirrels are native to the UK, whilst grey squirrels were introduced by the Victorians. Originally red squirrels populated much of the UK but over time grey squirrels populations have expanded. Rather than coexisting we have seen the grey squirrels replace red squirrels as they are larger, and better able to compete for food and habitats.

Skip to 1 minute and 57 seconds Grey squirrels also carry squirrelpox. This disease is usually fatal to red squirrels but isn’t harmful to the grey squirrels. The combination of habitat loss, disease, and the presence of the grey squirrel means that the red squirrel is now only found in pockets across the UK, such as the Lake District, Anglesey and sites in Scotland. There are around 140,000 red squirrels left in the UK, versus the 2.5 million grey squirrels. Given the low numbers of red squirrels, scientists are using this understanding of the two species to introduce management plans aimed at protecting the remaining populations of red squirrels.

Skip to 2 minutes and 32 seconds This example demonstrates the complexity of the interactions that often occur between species, but also the beneficial impact that working as an ecologist can have.


Understanding how organisms interact with members of the same species and others is key to implementing effective conservation strategies.

In this video we consider why biologists want to study populations, the things we can learn about them and how we can apply our knowledge of species biology to the implementation of management strategies and conservation efforts that can protect vulnerable species. Our case study in this video focuses on red squirrels, the threat that grey squirrels pose to them, and how we can use our understanding of species interactions and competition to protect red squirrels.

Here are some questions to consider while you’re watching the video. We’d be happy to hear your views after you’ve watched the video.

  • What do you think biologists mean by the term life history traits? Which types of factors do biologists want to investigate to understand the role of an organism in an ecosystem, how it interacts with other organisms and the threats that it faces?

  • The blue tit (Cyanistes caeruleus) is a common bird found in gardens and woods across the UK and across other parts of the globe. Which organisms might this bird compete with and what might this competition be for?

  • Imagine you are one of the scientists developing a management plan to help conserve the UK’s red squirrel population. What would you suggest doing and why?

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The Biology of Bugs, Brains, and Beasts

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