Populations and Sustainability

what is carrying capacity

• the maximum stable population size of a species ecosystem

• brought about due to abiotic and biotic factors that prevent every individual in a population from reaching adulthood and reproducing

what is environmental resistance

the combined effects of limiting factors that prevent further increase of a population

abiotic factors affecting population size

• light availability

• water supply

• water mineral content

• temperature

• amount of available space

• soil pH

example of how temp affects population size

• if temp is lower/higher than optimum, more energy required to maintain optimum body temp via homeostasis

• each individual has less energy available for growth and reproduction→ fewer individuals successfully reproduce= population growth limited

biotic factors affecting population size

• interspecific competition

• intraspecific competition

• predation

interspecific competition’s affect on population sizes

• in some cases, population sizes of both populations are limited→ usually if the two species are similarly well-adapted to the habitat

• in other cases, it can lead to a decrease in population size of one species and an increase in the other→ usually if one species is able to out-compete the other for resources and has a greater chance of survival and reproduction

intraspecific competition’s affect on population size

• when resources are plentiful, population of species increases

• more individuals for the same amount of resources

• resources eventually become limiting and due to competition, population can no longer grow in size→ carrying capacity reached

effects of competition

• competitive exclusion

• resource partitioning

• character displacement

competitive exclusion

• one species may be slightly better adapted to compete than the other, so other species can starve or not find habitat

• second species would move to different niche→ can evolve over generations and adapt to new niche

resource partitioning

• a particular resource is divided up to satisfy the needs of different feeders e.g. fruit is eaten by one species, leaves eaten by other species

• two species not directly competing for fruit but coexisting on different parts of it

character displacement

• closely related species that occupy similar niches in the same geographical region differentiate to avoid comp. exclusion

• e.g. galapagos finches have different beak dimensions to eat different sized seeds

predators

consumers that kill and eat other animals

prey

animals eaten by predators

predator-prey relationships

• in stable community, numbers of predators and prey rise and fall in cycles:

  • more prey available= # predators increases

  • more predators= # prey decreases

  • less prey= #predators decreases

  • less predators= # prey increases

conservation

• maintaining biodiversity and sustainability

• allowing human activity alongside other species in a managed way

preservation

• maintaining habitats and populations exactly as they are

• making no allowance for usage by humans

reasons for conserving biological resources

• moral obligation

• supply of important natural resources e.g. wood

• employment

• supply of food

• economic benefits

ecological reasons for conservation

• more divers ecosystem is better able to survive and adapt to environmental changes/ threats

• communities have keystone species that, when lost, have several knock on effects e.g. habitat loss

environmental reasons for conservation

• humans need diverse ecosystems due to the environmental services they provide

• Plants absorb CO₂ from atmosphere and help reduce greenhouse effect and climate change

• microorganisms digest and break down masses of organic waste produced by larger organisms

• fungi and bacteria are major part of nutrient cycle for further plant growth

• plants are both direct and indirect energy sources for humans

economic reasons for conservation

• many of the medicines used today have originated from plants, fungi and bacteria

• ecotourism is a major source of income for many countries→ provides jobs and contributes to economy

• ecosystems have made major contributions to science and technology

aesthetic reasons for conservation

• humans find joy and pleasure in the beauty of nature

• inspires creatives e.g. photographers, poets, musicians etc.

ethical reasons for conservation

• many believe humans have moral obligation to prevent loss of biodiversity

• planet shared with millions of other species and have no right to cause extinction of other species

• as humans are most intelligent species, responsibility falls on our shoulders

social reasons for conservation

• people enjoy spending time in the natural environment

• activities people can do e.g. mountain climbing, birdwatching

what is sustainability

the ability of an ecosystem to maintain its biodiversity whilst providing humans with resources they need over a long period of time

what must managed ecosystems achieve

• resource must be allowed sufficient time to replenish before being harvested so it does not run out

• no harm should be done to the ecosystem, its surrounding areas or the species living in it

• long-term future of the ecosystem must be guaranteed

examples of managed ecosystems for sustainability

• commercial fishing

• timber production

commercial fishing

• establishing fish quotas

• agreeing areas of ocean where fishing is banned and areas where it is permitted

• regulating mesh size of nets

• limiting size of fishing fleet by issuing licenses

• inspecting catch as a fishing boat returns to port

• banning certain practices e.g. gill nets

sustainable management for fast growing trees

• creation of clearing, firebreaks, selective felling, strip felling and edge habitat creation in conifer monocultures attracts other species and boost biodiversity

• genomic research has identified subspecies of spruce that can grow faster and shorten breeding process

• reaction and public education projects

coppicing and pollarding

felling techniques used to sustainably manage slower growing trees

coppicing

• felling trees close to the ground and leaving the stump in the ground→ new shoots can grow and can be harvested after around 7 years

• woodlands coppiced on rotation so only small areas lack mature growth

• means light can reach ground= more diverse woodland

pollarding

• similar to coppicing but trees cut 2-3m above ground

• similar benefits to coppicing but stops herbivores from eating new shoots as they grow

effects of human activities influencing animal and plant populations

• climate change

• introduction of non native species

• hunting

• degradation and loss of habitats

burning fossil fuels

• increases CO₂ levels in the atmosphere= global warming:

  • changes in weather patterns

  • melting polar ice caps

  • rising sea levels

  • rising ocean temps and acidity

• change habitats of some species, putting survival at risk

introduction of species

• occurs due to travel, keeping animals as pets, growing attractive plants in gardens, biological pest control

• non-native species often have no competitors, predators or pathogens to limit pop. growth→ can negatively affect native species

hunting

• can result in overexploitation of natural resource→ can result in extinction

• harvesting animals for food must carried out in a sustainable way to ensure extinction does not occur

habitat loss

• humans cut down forests and drain wetlands to create land for farming

• habitat area reduced so species will:

  • search for other habitats

  • compete for remaining habitat

• range of habitat can become so small that species cannot survive and becomes extinct

controlling the effects of human activities

• prohibiting import and export of species

• putting restrictions in place to control impact of humans on animal and plant populations

• reducing sources of greenhouse gases

• increasing capacity of carbon sinks e.g. oceans, forests, soil

balancing human needs and conservation

• a conflict exists between human needs and conservation

• conservation and sustainable practices can limit human needs in the short term

• careful management of natural resources is required to ensure humans use them sustainably but in a way that fulfils their current needs

change in food demand

• requirement to produce more food to support pop. growth meant:

  • farms began the practice of monoculture

  • more cereals grown rather than veg

  • fields made bigger to accommodate large machinery by removing hedgerows

  • wetland drained and ponds filled to turn land to arable

  • use of pesticides and fertilisers increased

effects of modern farming on biodiversity

• major negative impact on level of biodiversity present in farming areas

• conservationists have made strong efforts to maintain or improve biodiversity around farmlands:

  • areas have been rewilded

  • organic farming is promoted

  • hedgerows and field margins established

sowing of cereal crops

• smaller gap between harvesting and ploughing since modern farming means there is a short period of time during the year when food is plentiful for birds

• switch from spring to autumn sewing reduces diversity of farmland birds in the future

organic farming

• free from chemicals e.g. pesticides and inorganic fertilisers

• reduction in use of chemicals is thought to boost biodiversity in farms

• less productive than intensive farming, but more sustainable

biodiversity vs profit

• high yield and profit make farming viable

• difficult to find balance between conservation and farming due to decrease in biodiversity

• EU has grant schemes to encourage farmers to use more environmentally friendly farming techniques