Multiple factors acting at various levels of organisation, from species to landscapes, will interact to determine resilience capacity. For example, a species’ sensitivity to environmental change, its rate of population increase, its genetic variability and its phenotypic plasticity (i.e. the ability of a species to adjust its characteristics in response to its environment) are properties that underpin resilience (these are described in more detail in SoE 2011). At the landscape level, the amount of intact habitat, connectivity, and variation (or heterogeneity) in the landscape are important properties affecting resilience (Oliver et al. 2015; see Box BIO22). Show Adaptive capacity, which is often used to refer to the set of preconditions that enable species and systems to respond to climate change, is a synonym for many characteristics of resilience. To be resilient, species, communities and systems must generally be able to buffer disturbance, reorganise and renew after disturbance, and learn and adapt. For some parts of Australia’s biodiversity, it is changes in habitat condition that most affect their resilience, whereas in other parts of their range it is changes in habitat extent. For example, in Australia during the past 5 years, we have continued to observe continental-scale decreases in migratory shorebirds. Shorebirds migrate to Australia from Siberia and northern Alaska by a migration corridor known as the East Asian–Australasian Flyway (EAAF), which is used by more than 5 million shorebirds of almost 40 species. In 2016, an analysis of decadal timeseries of surveys of these species around Australia (Clemens et al. 2016) showed that numerous species are decreasing, some at alarming rates. The analyses examined population trends at inland and coastal sites around Australia for 19 species from 1973 to 2014. Continental-scale population decreases were identified in 12 of the 19 species, and regional-scale decreases (southern Australia) in 17 of the 19 species since 2000. Although some habitat modification has happened in Australia, vast areas of feeding grounds in Asia continue to be reclaimed, significantly reducing the ability of these birds to successfully complete their migrations (Iwamura et al. 2013; Murray et al. 2014, 2015). Tasmania is the southernmost destination in the EAAF, with observed long-term decreases exceeding those observed on the Australian mainland (see Box BIO13). New research into climate adaptation services has identified the ecological mechanisms and traits that support the intrinsic resilience of ecosystems, and facilitate their capacity to adapt and transform in response to change (Lavorel et al. 2015). Using 4 contrasted Australian ecosystems, this research suggests that 4 main mechanisms—vegetation structural diversity, the role of keystone species or functional groups, response diversity, and landscape connectivity—underpin the maintenance of ecosystem services and the reassembly of ecological communities under increasing climate change and variability. For the grassy eucalypt woodlands of south-eastern Australia, the highest priority for anticipated future pressure is maintaining perennial vegetation to reduce the risk of future desertification. For the Littoral Rainforest and Coastal Vine Thickets of eastern Australia, the maintenance of intact, diverse, connected forest stands of good quality is considered the key management requirement to support ecosystem adaptation. For the Australian Alps and South Eastern Highlands of south-eastern Australia, a greater management focus on fire-sensitive ash-type eucalypt forests, including fire suppression, fuel reduction and reseeding, is recommended. However, novel approaches to management may need to be considered in the future, such as translocating seed from resprouting montane species rather than fire-sensitive ash species. The Murray–Darling Basin contains floodplain woodlands and forests, consisting of few flood-tolerant and drought-tolerant eucalyptus and acacia species, as well as riparian woodland corridors, and chenopod shrubland and grassland in more arid regions. The study suggests that floodplain ecosystems are likely to persist under climate change, although with reduced extent and altered vegetation structure, and limits on water diversions and the restoration of water into the river systems will provide the greatest ecosystem resilience. Australian scientists recently identified the 10 major terrestrial and marine ecosystems in Australia that they considered most vulnerable to tipping points (Laurance et al. 2011):
Key factors predisposing these ecosystems to tipping points include:
The researchers emphasised that most vulnerable ecosystems were influenced by multiple drivers, such as climate change and extreme events, changes in fire regimes, invasive species and land-use pressures.
Biogeography is an ecological field of interest that focuses on the distribution of organisms and the abiotic factors that affect them.
Explain the role of biogeography in the analysis of species distribution Key TakeawaysKey Points
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Biogeography is the study of the geographic distribution of living things and the abiotic (non-living) factors that affect their distribution. Abiotic factors can include temperature, moisture, nutrients, oxygen, and energy availability, as well as disturbances from events such as wind and fire. Differences in temperature and rainfall are primarily based on latitude and elevation. As these abiotic factors change, the composition of plant and animal communities also changes. For example, if you were to begin a journey at the equator and walk north, you would notice gradual changes in plant communities. At the beginning of your journey, you would see tropical wet forests with broad-leaved evergreen trees, which are characteristic of plant communities found near the equator. As you continued to travel north, you would see these broad-leaved evergreen plants eventually give rise to seasonally-dry forests with scattered trees. You would also begin to notice changes in temperature and moisture. At about 30 degrees north, these forests would give way to deserts, which are characterized by low precipitation. Moving farther north, you would see that deserts are replaced by grasslands or prairies. Eventually, grasslands are replaced by deciduous temperate forests. These deciduous forests give way to the boreal forests found in the subarctic, the area south of the Arctic Circle. Finally, you would reach the Arctic tundra, which is found at the most northern latitudes. This trek north reveals gradual changes in both climate and the types of organisms that have adapted to environmental factors associated with ecosystems found at different latitudes. However, different ecosystems exist at the same latitude due in part to abiotic factors such as jet streams, the Gulf Stream, and ocean currents. If you were to hike up a mountain, the changes you would see in the vegetation would parallel those as you move to higher latitudes. Ecologists who study biogeography examine patterns of species distribution. No species exists everywhere. For example, the Venus flytrap is endemic to a small area in North and South Carolina. An endemic species is one which is naturally found only in a specific geographic area that is usually restricted in size. Other species are generalists, living in a wide variety of geographic areas. The raccoon, for example, is native to most of North and Central America. Species distribution patterns are based on biotic and abiotic factors and the influences these factors have had during the very long periods of time required for species evolution. Therefore, early studies of biogeography were closely linked to the emergence of evolutionary thinking in the eighteenth century. Some of the most distinctive assemblages of plants and animals occur in regions that have been physically separated for millions of years by geographic barriers. Biologists estimate that Australia, for example, has between 600,000 and 700,000 species of plants and animals. Approximately 3/4 of living plant and mammal species are endemic species found solely in Australia.
 Endemic species of Australia: Australia is home to many endemic species. The (a) wallaby (Wallabia bicolor), a medium-sized member of the kangaroo family, is a pouched mammal, or marsupial. The (b) echidna (Tachyglossus aculeatus) is an egg-laying mammal. Sometimes ecologists discover unique patterns of species distribution by determining where species are not found. Hawaii, for example, has no native land species of reptiles or amphibians and has only one native terrestrial mammal, the hoary bat. Most of New Guinea, as another example, lacks placental mammals. Plants can be endemic or generalists. Endemic plants are found only in specific regions of the earth, while generalists are found in many regions. Isolated land masses, such as Australia, Hawaii, and Madagascar, often have large numbers of endemic plant species. Some of these plants are endangered due to human activity. The forest gardenia (Gardenia brighamii), for instance, is endemic to Hawaii; only an estimated 15–20 trees are thought to exist.
Endangered forest gardenia: Listed as federally endangered, the forest gardenia is a small tree with distinctive flowers. It is found only in five of the Hawaiian Islands in small populations consisting of a few individual specimens.
The availability of energy and nutrient sources affects species distribution and their adaptation to land or aquatic habitats.
Assess how energy availability affects species distribution within an ecosystem Key TakeawaysKey Points
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Energy from the sun is captured by green plants, algae, cyanobacteria, and photosynthetic protists. These organisms convert solar energy into the chemical energy needed by all living things. Light availability can be an important abiotic force directly affecting the evolution of adaptations in photosynthesizers. For instance, plants in the understory of a temperate forest are shaded when the trees above them in the canopy completely leaf out in the late spring. Not surprisingly, understory plants have adaptations to successfully capture available light. One such adaptation is the rapid growth of spring ephemeral plants, such as the spring beauty. These spring flowers achieve much of their growth and finish their life cycle (reproduce) early in the season before the trees in the canopy develop leaves.
Ephemeral plant: The spring beauty is an ephemeral spring plant that flowers early in the spring to avoid competing with larger forest trees for sunlight. In aquatic ecosystems, the availability of light may be limited because sunlight is absorbed by water, plants, suspended particles, and resident microorganisms. Toward the bottom of a lake, pond, or ocean, there is a zone that light cannot reach. Photosynthesis cannot take place there and, as a result, a number of adaptations have evolved that enable living things to survive without light. For instance, aquatic plants have photosynthetic tissue near the surface of the water. The broad, floating leaves of a water lily cannot survive without light. In environments such as hydrothermal vents, some bacteria extract energy from inorganic chemicals because there is no light for photosynthesis. Nutrient CyclingThe availability of nutrients in aquatic systems is also an important aspect of energy or photosynthesis. Many organisms sink to the bottom of the ocean when they die in the open water. When this occurs, the energy found in that organism is sequestered for some time unless ocean upwelling occurs. Ocean upwelling is the rising of deep ocean waters that occurs when prevailing winds blow along surface waters near a coastline. As the wind pushes ocean waters offshore, water from the bottom of the ocean moves up to replace this water. As a result, the nutrients once contained in dead organisms become available for reuse by other living organisms.
Upwelling: Ocean upwelling is an important process that recycles nutrients and energy in the ocean. As wind (green arrows) pushes offshore, it causes water from the ocean bottom (red arrows) to move to the surface, bringing up nutrients from the ocean depths. In freshwater systems, the recycling of nutrients occurs in response to air temperature changes. The nutrients at the bottom of lakes are recycled twice each year: in the spring and fall turnover, which recycles nutrients and oxygen from the bottom of a freshwater ecosystem to the top of a body of water. These turnovers are caused by the formation of a thermocline: a layer of water with a temperature that is significantly different from that of the surrounding layers. In wintertime, the surface of lakes found in many northern regions is frozen. However, the water under the ice is slightly warmer, while the water at the bottom of the lake is warmer yet at 4 °C to 5 °C (39.2 °F to 41 °F). Water is densest at 4 °C; therefore, the deepest water is also the densest. The deepest water is oxygen poor because the decomposition of organic material at the bottom of the lake uses up available oxygen that cannot be replaced by means of oxygen diffusion into the water due to the surface ice layer. In springtime, air temperatures increase and surface ice melts. When the temperature of the surface water begins to reach 4 °C, the water becomes heavier and sinks to the bottom. The water at the bottom of the lake, displaced by the heavier surface water, rises to the top. As it rises, the sediments and nutrients from the lake bottom are brought along with it. During the summer months, the lake water stratifies, or forms layers, with the warmest water at the lake surface. As air temperatures drop in the fall, the temperature of the lake water cools to 4 °C; this causes fall turnover as the heavy cold water sinks and displaces the water at the bottom. The oxygen-rich water at the surface of the lake then moves to the bottom of the lake, while the nutrients at the bottom of the lake rise to the surface (). During the winter, the oxygen at the bottom of the lake is used by decomposers and other organisms requiring oxygen, such as fish.
Nurient recycling in freshwater systems: The spring and fall turnovers are important processes in freshwater lakes that act to move the nutrients and oxygen at the bottom of deep lakes to the top. Turnover occurs because water has a maximum density at 4 °C. Surface water temperature changes as the seasons progress, causing denser water to sink.
Temperature and water are important abiotic factors that affect species distribution.
Describe species adaptations to temperature fluctuations and the availability of water Key TakeawaysKey Points
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Temperature affects the physiology of living things as well as the density and state of water. It exerts an important influence on living organisms because few can survive at temperatures below 0 °C (32 °F) due to metabolic constraints. It is also rare for them to survive at temperatures exceeding 45 °C (113 °F). This is a reflection of evolutionary response to typical temperatures. Enzymes are most efficient within a narrow and specific range of temperatures; enzyme degradation can occur at higher temperatures. Therefore, organisms must either maintain an internal temperature or inhabit an environment that will keep the body within a temperature range that supports metabolism. Some animals have adapted to enable their bodies to survive significant temperature fluctuations, as seen in hibernation or reptilian torpor. Similarly, some bacteria have adapted to survive in extremely-hot temperatures found in places such as geysers. Such bacteria are examples of extremophiles: organisms that thrive in extreme environments. Temperature can limit the distribution of living things. Animals faced with temperature fluctuations may respond with adaptations, such as migration, in order to survive. Migration, the movement from one place to another, is common in animals, including many that inhabit seasonally-cold climates. Migration solves problems related to temperature, locating food, and finding a mate. In migration, for instance, the arctic tern (Sterna paradisaea) makes a 40,000 km (24,000 mi) round trip flight each year between its feeding grounds in the southern hemisphere and its breeding grounds in the Arctic Ocean. Monarch butterflies (Danaus plexippus) live in the eastern United States in the warmer months, but migrate to Mexico and the southern United States in the wintertime. Some species of mammals also make migratory forays: reindeer (Rangifer tarandus) travel about 5,000 km (3,100 mi) each year to find food. Amphibians and reptiles are more limited in their distribution because they lack migratory ability. Not all animals that can migrate do so as migration carries risk and comes at a high energy cost.
Arctic tern: The arctic tern is an example of a species that must migrate yearly to deal with temperature fluctuations that exist in the regions where it is found. Some animals hibernate or estivate to survive hostile temperatures. Hibernation enables animals to survive cold conditions, while estivation allows animals to survive the hostile conditions of a hot, dry climate. Animals that hibernate or estivate enter a state known as torpor, a condition in which their metabolic rate is significantly lowered. This enables the animal to wait until its environment better supports its survival. Some amphibians, such as the wood frog (Rana sylvatica), have an antifreeze-like chemical in their cells, which retains the cells’ integrity and prevents them from bursting.
Wood frog: The wood frog, like all other amphibians and reptiles, cannot migrate; as a result, the species survives extreme temperature changes through the antifreeze-like chemical found in their cells. WaterWater is required by all living things because it is critical for cellular processes. Since terrestrial organisms lose water to the environment by simple diffusion, they have evolved many adaptations to retain water. Examples of adaptations used by terrestrial and aquatic species include the following:
Marine iguanas: Marine iguanas have a special, salt-secretion adaption that allows them to minimize bodily water loss.
Soil structure, oxygen availability, wind, and fire are abiotic factors that have influences on species distribution and quantity.
Identify further abiotic factors that affect species distribution and abundance Key TakeawaysKey Points
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Inorganic nutrients, soil structure, and aquatic oxygen availability are further abiotic factors that affect species distribution in an ecosystem. The same is true for terrestrial factors, such as wind and fire, which can impact the types of species that inhabit regions exposed to these types of disturbances. Inorganic Nutrients and SoilInorganic nutrients, such as nitrogen and phosphorus, are important in the distribution and the abundance of living things. Plants obtain these inorganic nutrients from the soil when water moves into the plant through the roots. Therefore, soil structure (the particle size of soil components), soil pH, and soil nutrient content play an important role in the distribution of plants. Animals obtain inorganic nutrients from the food they consume. Therefore, animal distributions are related to the distribution of what they eat. In some cases, animals will follow their food resource as it moves through the environment. Oxygen Availability
Jack pine cones: The mature cones of the jack pine (Pinus banksiana) open only when exposed to high temperatures, such as during a forest fire. A fire will probably kill most vegetation, so a seedling that germinates after a fire is more likely to receive ample sunlight than one that germinates under normal conditions.
Some abiotic factors, such as oxygen, are important in aquatic ecosystems as well as terrestrial environments. Terrestrial animals obtain oxygen from the air they breathe. Oxygen availability can be an issue for organisms living at very high elevations, where there are fewer molecules of oxygen in the air. In aquatic systems, the concentration of dissolved oxygen is related to water temperature and the speed at which the water moves. Cold water has more dissolved oxygen than warmer water. In addition, salinity, water current, and tide can be important abiotic factors in aquatic ecosystems. Other Terrestrial FactorsWind can be an important abiotic factor because it influences the rate of evaporation and transpiration. The physical force of wind is also important because it can move soil, water, or other abiotic factors, as well as an ecosystem’s organisms. Fire is another terrestrial factor that can be an important agent of disturbance in terrestrial ecosystems. Some organisms are adapted to fire and, thus, require the high heat associated with fire to complete a part of their life cycle. For example, the jack pine, a coniferous tree, requires heat from fire for its seed cones to open. Through the burning of pine needles, fire adds nitrogen to the soil and limits competition by destroying undergrowth. Abiotic Factors Influencing Plant GrowthThe two most important abiotic factors affecting plant primary productivity in an ecosystem are temperature and moisture.
Identify the abiotic factors that affect plant growth Key TakeawaysKey Points
Key Terms
Temperature and moisture are important influences on plant production (primary productivity) and the amount of organic matter available as food (net primary productivity). Primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of chemical compounds as its source of energy. Almost all life on earth is directly or indirectly reliant on primary production. The organisms responsible for primary production, known as primary producers or autotrophs, form the base of the food chain. In terrestrial eco-regions, these are mainly plants, while in aquatic eco-regions, they are mainly algae. Net primary productivity is an estimation of all of the organic matter available as food. It is calculated as the total amount of carbon fixed per year minus the amount that is oxidized during cellular respiration. In terrestrial environments, net primary productivity is estimated by measuring the aboveground biomass per unit area, which is the total mass of living plants, excluding roots. This means that a large percentage of plant biomass which exists underground is not included in this measurement. Net primary productivity is an important variable when considering differences in biomes. Very productive biomes have a high level of aboveground biomass. Annual biomass production is directly related to the abiotic components of the environment. Environments with the greatest amount of biomass have conditions in which photosynthesis, plant growth, and the resulting net primary productivity are optimized. The climate of these areas is warm and wet. Photosynthesis can proceed at a high rate, enzymes can work most efficiently, and stomata can remain open without the risk of excessive transpiration. Together, these factors lead to the maximal amount of carbon dioxide (CO2) moving into the plant, resulting in high biomass production. The aboveground biomass produces several important resources for other living things, including habitat and food. Conversely, dry and cold environments have lower photosynthetic rates and, therefore, less biomass. The animal communities living there will also be affected by the decrease in available food.
Primary productivity and biomass production: The magnitude and distribution of global primary production varies between biomes. However, warm and wet climates have the greatest amount of annual biomass production. |
Which of the following are the two most important factors in determining a habitat’s climate?
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