Invertebrates and Climate Change – Implications for Biodiversity

Entomologist, Don Sands, gave a presentation on the effects of climate change on invertebrates at the June 2007 biannual Brunswick Valley Nature Festival. This is an edited transcript of his presentation *

 

Invertebrates are the smallest animals but they’re the largest group. In 1999 a publication titled The Other 99% (Conservation and Biodiversity of Invertebrates, Trans. Roy. Zool. Soc. NSW) was published to summarise conservation issues regarding the animal kingdom, particularly the invertebrates. With insects we are still talking about more than 75% of the animal kingdom. How many of us really think that way?

I’m going to talk about climate change as it is affecting insects today. Although you are probably more aware than most people of change in rainfall across the eastern coast of Australia, at the same time, you can’t do anything about the change in temperature – as the ocean temperature goes up, so do the air temperatures. Temperature rises have an enormous effect on the invertebrates, perhaps more rapidly than on plants and, as well, on most vertebrates. 

Climate change, which impacts on all Australian ecosystems, like coastal wetlands and mangroves, woodlands, grasslands, rainforests, hilltops and water courses, may stimulate different reactions. You can’t put a broad-brush definition of impacts across how these ecosystems will be affected by climate change but I believe that if you forget the impacts on insects, you risk losing the lot. You can be interested in the conservation of Koalas and the coxen’s fig parrot and many other wonderful creatures, but if you do not think about the invertebrates sharing their habitats, you may miss out on all the many connections which are very important. 

If an invertebrate responds to climate change, it will be rapid. Most insects are adapted to seasonal cycles, particularly in temperatures for their development, as well as to rainfall, humidity and light. These climatic variables also directly and indirectly interact with all other flora (especially phenotypic variation) and fauna. Most occupy specific ecosystems and need particular plant species for survival, food and reproduction. Those insects survive in a broad range of habitats and can move more easily from one habitat to another, but a lot of habitat remnants are little areas and are therefore at a greater risk, especially if the species is not very mobile. We don’t hear a lot about the effects on biodiversity from an increase in carbon dioxide, but it is likely to lower the nutrient uptakes in plants, and directly affect herbivorous insect species feeding on them, and perhaps larger creatures like koalas. Diseases which are becoming more prominent in koalas, for example, may be due to stresses from changes in nutrients in their host trees – a sound hypothesis!

It is sad that invertebrates are not already being used as environmental indicators. We should pressure the authorities to do this, and to start now, before it is too late. Insects react very quickly to climate and it is known worldwide that their presence, or absence, can indicate environmental change. They have quick reproductive cycles and their rates of increase are generally high when compared with animals. The appearance and disappearances of ‘apparent’ species are easily monitored, particularly species which are adapted to specialist ecosystems or altitudes. If an insect and a plant exist at very high altitudes, and the temperature increases, they may have nowhere to go when temperatures increase if they cannot adapt to change. The disappearance of those temperature-sensitive insect species and plants will be the best indicators for predicting extinctions.  We have an eastern coastal band of wet and dry pockets driving the distribution and variation in flora, and many species of the invertebrates. The macropods and larger vertebrates are often much more mobile, can escape threats, and move to new habitats. Abrupt changes in distribution of these organisms and plants are not so great inland due to extremes of temperature and rainfall; they exist over larger areas because the climate variations are not so abrupt. You live in a pocket of rainfall in eastern Australia, ranging roughly from Iluka, NSW, to Maryborough, Queensland, with the ‘hot hole’ rain-shadow of Brisbane (Beenleigh to Bribie Island) in the middle.

All groups (about 29 orders) of insects will be affected by climate change. We have to think about the different roles of these insects to understand how their loss or change in species will affect the survival of other plants and animals. 

There is a range of pollinators, like native bees, flies, beetles, wasps and fig wasps, which are important pollinators for different groups of plants. There are small flies that pollinate the genus Cryptocaria for example. Eucalypts have range of different insect pollinators as well as vertebrate pollinators. 

Herbivores feed on different parts of plants – foliage and sap feeders, timber and grass for termites, crickets, grass hoppers, beetles, sawflies, moths, butterflies for leaves and stems, thrips, phasmatids and bugs are extremely important for their impacts on natural plant growth and architecture. Stem borers like beetles, termites and moths are important food for the black cockatoos. 

Seed dispersers like bees, ants and others and detritivores (see Detritivores, right) and nutrient recyclers like moths (e.g the oecophorids), beetles, flies, ants, springtails (see Springtails, right), cockroaches, termites, web spinners, booklice, diplura and silver fish, all have impacts on other organisms easily overlooked unless they are pests! Predators and parasitoids (e.g. wasps), flies, moths and butterflies, bugs, beetles, cockroaches, mantids, crickets, lice, dragonflies, mayflies, earwigs, dobsonflies, lacewings, scorpion flies, fleas and damsel flies, all contribute to stability of our invertebrate populations.  

Because most invertebrates have massive reproductive capabilities, the only thing that stabilises their populations is their own suite of natural enemies and without these many become pests. Predators and parasites often only attack one species of host, a relationship that evolved for up to 45 million or more years ago – essential interactions stabilising our environmental health. 

When farmers justifiably shout long and hard about the recent drought,  environmentalists should be aware of what’s going on where they are trying to grow crops. If I look at the distribution, or zones, of most insects on the east coast we find that they fit into the wet and dry belts up and down the east coast, more so than the inland or southern species. This makes our subtropical environment for invertebrates very special but also vulnerable to climate change. We have a huge biodiversity of insects, not just overlapping in the distribution of tropical and temperate species, but the biodiversity is unique to the subtropics.

Increasing temperatures will affect distributions of insect species and many will depend on relocation, through intact, to find suitable habitats; habitats will not be able to move because the change in temperature of a couple of degrees may cause their related species to disappear. Relocation will depend upon, food, shelter, suitable temperature ranges, habitats – and compatible natural enemies. Sustained breeding will require necessary genetic variability in the founders and new natural enemy complexes must be able to co-exist in the new habitats. Host shifts or changes are likely, for example cycads and butterflies. Some benign insects will become pests and some pests might decline locally or be replaced by others. 

Subtropical vine forests are very important for insect biodiversity and many insects of conservation interest are reliant on vines. I would like to ask the rainforest regenerators, “how many vinesthey plant in their rehabilitation plots?” Vines are a essential part of the subtropical rainforests and desiccate readily. Some may not be easily propagated but many vines are major food plants for butterflies and moths, more so than trees. Rainforests without vines are not rainforests, yet vines are not popular with bush regenerators. Some rainforest vines are becoming rare; others are poorly represented in protected areas and previously common vines are disappearing.  Vines are likely to be the most affected plants by climate change, with many weedy species ready to move in on weakened native species.

We should begin mappingdistributions and corridors for our fauna and flora. I am very worried that in none of the states are we mapping invertebrate distribution so that we can identify species at risk of disappearing when they cannot move from one climatic zone to another. We can’t plan for this if we don’t know where they are. Then we need to predict to where species might move and re-colonise, under pressures of climate change, or because of disturbance. 

We must manage fire more effectively, reduce its impacts and areas consumed, provide better protection and refuges for sensitive species as well as re-examine the advantages of traditional fuel reduction practices.

Some native pest species will become more important, for example, the fruit-piercing moth (Eudocima fullonia) whichhas a modified proboscis like a drill bit, which can fly 2,000 km every year from the tropics of north Queensland south to create havoc in this area. People who grow lychees have a lot of trouble with them. The problem with this moth is that it is a tropical species but it breeds very quickly and migrates south. It normally dies out in cold winters but what will happen if the temperatures increase by 2 degrees Centigrade in winter? We have developed models to predict that this moth could then overwinter in southern areas and create havoc in early-season commercial. Parasites, predators and diseases are essential for regulating all known pest numbers. An example is Euplectrus melanocephalus, a parasitic wasp, a larval parasitoid of Eudoclma spp.. Without these wasps some native species like fruit-piecing moths are likely to become more serious pests through loss of natural enemies. Climate change could devastate a whole system.

One threatened species of moth, perhaps the best known in this area, is the pink underwing moth (Phyllodes imperialis). It is as big as the richmond birdwing nutterfly and it has extraordinary caterpillars that survive only in shaded, moist, old growth rainforest, where they evolved millions of years ago, possibly to escape UV light. The caterpillar is very large, and strangely shaped; we believe it resembles a lizard! It only feeds on one subtropical vine, Carronia multisepalea. Climate change could easily drive this rare moth to extinction by drying out the rainforest habitats by reducing shade, or influencing the leaf quality that is known to have effects on survival of the caterpillars.

Prolonged drought has the most serious impact on a group of invertebrates that survive through cold winters in diapause. Diapause is related to hibernation, and species that enter diapause will be seriously affected by climate change. These may naturally be ‘switched on’ by increases in temperatures in spring, and when days get longer and temperatures higher. A third trigger that may turn off breaks in diapause in invertebrates will be extended gaps between rain events. What happens if you have drought and those in diapause become active, but they begin hatching over a longer period? Half of them may not find mates in time to reproduce; inbreeding depression may follow sibling mating and massive declines in numbers follow because they become sterile.

There are other special issues for insects with humidity changes. Leaf litter arthropods and other detritivores are affected by declines in the moisture of leaves, soils and timber, and cloudless days and lowered humidity can affect the dispersal and re-colonisation of disturbed habitats. Low densities of adults spread out over time are threatening many species, with inbreeding depression occurring in creatures like the richmond birdwing butterfly. Coastal populations of the richmond birdwing have two adult generations in one year, with all over-wintering only as pupae in diapause. Winter and spring droughts cause this diapause to protract and low densities of adults emerge from pupae between October and December instead of December. This is a serious issue which does not just affect the richmond birdwing but a whole other range of insects. I see inbreeding depression and genetic debilitation as two of the major conservation issues, not just of insects, but of plants as well.

In north QLD there is a small oecophorid moth, Trisyntopa scatophaga, which lives in the termite mound nests of the golden shouldered parrot. The larvae feed on the parrot’s faeces andthe legs of the birds clean. The moths diapause as larvae whose cycle is synchronised with the nesting season of the threatened parrot by day length, temperature and rainfall. Climate change on Cape York could disrupt the moths’ emergence. This moth has no other host and no other life history. The hooded parrot which lives in termite mounds south of Darwin is similar and has its own species of moth.  Could this be why the paradise parrot became extinct? The paradise parrot was in this area once; did it have a moth whichthe birds clean too?weremany termite mounds here at the time, before they wereup and used in footpaths and tennis courts, or their habitats cleared. One of the threats to the paradise parrothave beenremoval of the mounds but another threat may well have been the removal of its moth.

A butterfly on the verge of extinction is the australian fritillary butterfly, Argyreus hyperbius inconstans, and it last seen in Qld in 2004. It needs abundant clumps of the wild(Viola betonicifolia) found in coastal, open sedge wetlands, which are very prone to drought and invasion of exotic weeds, especially grasses like seteria and green panic grass. This butterfly is on the skids in a big way. Low plant densities can explain some fritillary extinction but larval diapause and drought arethe main reason for its irregular ‘boom and bust’ abundance.

Herbivorous insects are important modifiers of plant architecture and recyclers of nutrients. Important herbivores feed on eucalypts and Acacias; they greatly modify tree growth. The rare rainforest beetle spiloyra breeds on moist, young grevilleas. They are humidity dependent and will not breed when it is dry.

When weeds invade:

  • Higher temperatures stimulate competitive growth. Exotic grasses out compete native grasses and sedges, reduce seedling survival and threaten terrestrial ecosystems.
  • During drought weed survival rates are higher than those of natives.

Grassy weeds are denser, taller and are more flammable than native species:

  • Exotic vines smother food-plant vines, native vines, shrubs and trees. They prevent seedling survival and young growth.

Weeds have few or no insect herbivores to attack them. Many weeds reduce the effectiveness of insects’ natural enemies by repelling them. Weeds are often poisonous to insects, trap them or detrimentally influence their behaviour, like the poisonous dutchman’s pipe vine that the richmond birdwing larvae will feed on.

A lot of the insects that graze the introduced grasses or weeds, or break them down to recycle nutrients into the soil, have not been introduced with the weed.

Fire is a touchy subject with fire managers but it will have increased impacts on the environment with climate change. Immature and immobile life stages are vulnerable to winter burning and cannot escape from these fires. Increased fire regimes will kill insects when most of them are dormant. Colonies are often wiped out when habitats are burnt. When moths lose habitat through fire, survival then depends on them sheltering in suitable refuges, or migrating from unburnt locations. Vertebrates can be lost when moths, in their various life stages, become a scarce food source.  Increased fire will cause more fragmentation of habitats – increased genetic isolation in insects and their food plants, and loss of genetic variability, and inbreeding. We tend to burn off during winter when insects are less mobile and soil moisture is lowest but we will have to rethink our fire regime techniques if we want to reduce impacts on our small animal biodiversity. Practices have been given to us from farming and forestry and then grafted onto the urban environment but they took no account of climate change. We are told that this is “how the traditional occupants did it”, but this is not necessarily so; they were very careful by doing small burns and managing their bush to preserve their scarce food resources. Fire is becoming the biggest threat to invertebrates in dry eucalypt forest of all their threatening processes.

We have to teach our managers to understand that if they do broad scale burning at the frequency that they are doing in the mountain ranges, in the woodlands and in the grasslands, we are going to have massive effects on our invertebrates. These oecophorid moths not only break down nutrients but also reduce the fire load; their loss could create larger fuel loads and even more fires. Climate change and increased fire threatens all Australian ecosystems and is already converting flammable vegetation into more fire-prone and biologically-poor remnants. Nutrients, especially nitrogen and potassium, are progressively lost after increases in fire frequencies when plants cannot keep up with absorbing them. Each ecosystem is being threatened by a loss of a complex of oechophorid moth species, especially in flammable eucalypt plant communities. Frequent fuel-reduction burning promotes fire-adapted plant survival and in the longer term increases the fuel loads. Fire regime practices must change.

 

Climate change prompts us to review the threats to our environment. Healthy insects equal a health environment. We need to:

  • reduce human disturbance and develop threat abatement strategies for all terrestrial, aquatic and riparian systems
  • protect, expand and manage ‘secure’ animal and plant refuges (national parks, etc)
  • rehabilitate disturbed habitats to restore specialised species needs – including soil quality, water tables and moisture, symbiotic relationships and review natural nutrient recycling

explore alternative methods for weed management, including controlling invasive environmental weeds with bio-controls. We need to think more carefully than just pulling out weeds. Herbicide and removal does not work in the long term on camphor laurel, privet, chinese elm or exotic pines. Biocontrol has to be done for environmental weeds as it is done for the ‘economic’ plants. The only reason that camphor laurel and privet are weeds is that all their seeds are viable. If we can get insects to break down the seeds then we can break the reproductive cycle. There are a range of biological control insects in China and Japan which decimate the camphor laurel seeds. Weedy and flammable grasses, like gamba grass, molasses, green panic, buffalo and lovegrass need to be considered as targets for biological control. The umbrella tree, privets, camphor laurel and chinese elm have become weeds in this area, all excellent candidates for biological control of their seeds.

We can learn to live with climate change if we plan for it, know what the problems are, and start to put into place mitigation methods to address those issues.

 

 

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