Discuss the role of carrying capacity in determining population size in humans and other species [9 marks]

Indicative Content	Guidance
Carrying capacity: Defines the maximum sustainable population size Affects both humans and other species → but (often) in different ways Human populations: May be less influenced by limiting or density-dependent factors → in comparison to other species Exceeding carrying capacity (overshoot) can lead to decreased fertility / increased mortality / migration / famines / water shortages / environmental degradation Other species typically fluctuate around carrying capacity → rarely exceed carrying capacity Population growth patterns: Growth of human populations (often) follows a J-curve → most other species follow an S-curve Determining human carrying capacity is complex Humans can switch resources when they become limiting Technological advancements: Technology enhances resource efficiency for humans → human adaptability now outpaces evolutionary adaptations Population control: Humans can consciously control population growth Other species rely on natural processes Environmental variability: Carrying capacity for most species varies with weather / food availability → humans can adapt with technology / imports / resource switching Carrying capacity limitations vary geographically Consequences of overshoot (exceeding carrying capacity): Some species crash after population growth follows a J-curve → human populations may face a similar scenario	You will always have to answer two 9-mark questions from Section B in your IB ESS SL Paper 2 exam This is a 'level of response' answer. The examiner will award you a combined mark out of 9 for knowledge, application, analysis, and evaluation ‘Discuss’ (for 9 marks) requires: Knowledge of concepts, principles and models Application to the context using relevant and focused examples Analysis showing logical and coherent chains of reasoning of a range of issues Evaluation showing critical thinking linked to the context Depth is more important than breadth It is sensible to discuss two or three main points but to apply, analyse and evaluate them fully For top-level evaluation, informed judgement is required This can be demonstrated in a conclusion that synthesises and weighs up the arguments to form a supported answer to the question
Model Answer
The concept of carrying capacity, representing the maximum population size an environment can sustain over an extended period of time, plays an important role in determining population size for humans and other species [K]. As populations approach their carrying capacity, they experience density-dependent factors or limited resources, such as the availability of food and water [Ap]. Human populations may be less influenced by these factors compared to other species [An]. When human populations exceed their carrying capacity, various responses can occur, including increased mortality or increased migration. Events like famines, pandemics, or extended pollution may indicate that humans have exceeded their carrying capacity [Ap]. Other species rarely exceed their carrying capacity for extended periods. Unlike most species, human population growth does not typically follow an S-curve and then fluctuates around the carrying capacity. Instead, it often resembles a J-curve, where growth is not limited, as a lack of negative feedback leads to exponential growth [Ap]. Determining the carrying capacity of human populations is difficult due to their use of a wide variety of resources. Humans have the ability to quickly switch resources or import replacement resources when they become limiting, which sets them apart from many species that have a more limited range of available resources [An]. Technological developments enable greater efficiency in resource use by human populations, while most species rely on slow evolutionary processes to evolve to utilise resources more effectively [K]. Human mental and social skills allow rapid adaptation to changing conditions, in contrast to most other species. Humans can also take conscious actions, such as government policies, to control population growth [An]. There can be serious and unfortunate consequences for human populations that overshoot their carrying capacity. For some species such as r-strategists, following a J-curve may eventually lead to a population crash, and this is also a possibility for humans [An]. In some less economically developed countries, opportunities for resource switching or importing resources may be limited, making carrying capacity more limiting. Understanding these dynamics is crucial for sustainable population management of human societies, both on a national and global scale [E].
Commentary
This answer is an example - yours may be different The answer gives a balanced comparison of the influence of carrying capacity on human and non-human populations and finishes by considering the potential consequences of this for human societies The response is annotated to show where the skills of knowledge (K), application (Ap), analysis (An) and evaluation (E) have been demonstrated

Species & Populations (SL IB Environmental Systems & Societies (ESS))

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