Are There More Plant or Animal Species? - Plant Care Guide

When comparing known species, there are significantly more identified animal species than plant species on Earth. While the exact numbers are constantly changing as new discoveries are made, current scientific estimates suggest that animals, particularly insects, far outnumber plants in terms of described species. This disparity highlights the vast and often unseen biodiversity of the animal kingdom.

What Do We Mean by "Species" in Biology?

To accurately answer the question of whether there are more plant or animal species, it's crucial to first understand what "species" means in a biological context. The concept of a species is fundamental to biology and is used to classify and organize the immense diversity of life on Earth.

Defining "species":

• Biological Species Concept (BSC): The most widely accepted definition, particularly for animals, is the Biological Species Concept. This concept defines a species as a group of individuals that can interbreed in nature and produce fertile offspring. For example, a lion and a tiger can interbreed to produce a liger, but ligers are typically sterile, so lions and tigers are considered different species.
• Other Species Concepts: The BSC isn't perfect for all organisms:
  • Asexual organisms: It doesn't apply to organisms that reproduce asexually (like many bacteria, fungi, and some plants).
  • Fossil species: It's impossible to test interbreeding in extinct species.
  • Hybridization: Some distinct species can occasionally interbreed and produce fertile offspring (e.g., some plant species).
• Morphological Species Concept: Often used for plants, fossils, or organisms where interbreeding is hard to observe. It defines species based on shared physical characteristics.
• Phylogenetic Species Concept: Defines a species as the smallest group of organisms that shares a common ancestor and can be distinguished from other such groups.

Despite these complexities, when scientists count species, they are generally referring to distinct groups identified by one of these concepts. This classification allows us to track biodiversity and understand evolutionary relationships.

How Many Plant Species Have Been Identified?

The number of identified plant species is a continually evolving figure, as new discoveries are made, and classifications are refined. However, scientific efforts have documented a substantial and impressive diversity within the plant kingdom.

Current estimates for identified plant species:

• Around 390,000 to 435,000 vascular plant species: This is a commonly cited range, which includes flowering plants, conifers, ferns, and their allies. Vascular plants are those with specialized tissues for transporting water and nutrients.
• Flowering Plants (Angiosperms): Make up the vast majority, with estimates often exceeding 350,000 species. They are the most diverse group of plants.
• Non-vascular plants: (Bryophytes like mosses, liverworts, and hornworts) add tens of thousands more species, often bringing the total closer to half a million or slightly more.
• Ongoing Discovery: Botanists are still discovering new plant species, particularly in tropical rainforests and remote regions. On average, thousands of new plant species are described each year.

The total number of plant species is relatively well-cataloged compared to some other kingdoms, partly because plants are generally larger, stationary, and easier to collect and observe than many microscopic or elusive animal species. Despite this, significant undocumented plant diversity likely remains.

How Many Animal Species Have Been Identified?

The number of identified animal species dwarfs that of plants, primarily due to the immense diversity within certain animal groups. This figure is also in constant flux, but the overall trend shows a far greater number of animal forms.

Current estimates for identified animal species:

• Approximately 1.5 to 2 million identified animal species: This is a widely accepted range, though some estimates go higher.
• Insects Dominate: The vast majority of identified animal species are insects. They account for over a million described species, and many more are believed to exist undiscovered, especially in tropical regions. Beetles alone (Order Coleoptera) represent over 350,000 known species.
• Vertebrates: (Mammals, birds, reptiles, amphibians, fish) make up a comparatively small fraction, with around 66,000 identified species. We are still discovering new vertebrates, but at a much slower rate than invertebrates.
• Other Invertebrates: Groups like mollusks, crustaceans, arachnids (spiders, mites), nematodes (roundworms), and annelids (segmented worms) contribute hundreds of thousands of identified species.
• Vast Unknowns: Scientists believe that the identified species represent only a fraction of the total animal species on Earth. Estimates for the total number of animal species (identified and unidentified) range widely, from 5 million to over 30 million, with some even pushing towards 100 million, primarily due to the estimated number of undescribed insects, nematodes, and marine invertebrates.

The sheer volume of animal species, particularly invertebrates, makes them the more numerous group in terms of documented biodiversity.

What Factors Influence the Discovery and Identification of New Species?

The process of discovering and identifying new species is a complex and ongoing endeavor influenced by a multitude of factors. These factors can either accelerate or hinder our understanding of Earth's total biodiversity, contributing to the perceived differences in the numbers of known plant and animal species.

Key factors influencing species discovery:

• Size of the organism: Larger, more conspicuous organisms (like mammals, birds, and large trees) are generally easier to find and have been largely documented. Tiny organisms (insects, nematodes, microbes) are far more challenging to spot and categorize.
• Mobility: Stationary organisms (plants, fungi) are easier to locate, collect, and study in a given area than mobile ones (animals), which might require more specialized tracking methods.
• Habitat accessibility: Remote, deep-sea, underground, or canopy habitats are difficult and expensive to explore, meaning much biodiversity in these areas remains unknown.
• Research effort and funding: The number of taxonomists (scientists who classify species), the resources available for expeditions, and technological advancements (e.g., DNA sequencing) directly impact the rate of discovery.
• Ease of distinction: Some groups have clear morphological differences, making new species easier to identify. Other groups (like many insects or fungi) have cryptic species that look identical but are genetically distinct, requiring more detailed analysis.
• Economic importance: Species with direct economic value (e.g., agricultural pests, medicinal plants, commercially fished species) often receive more research attention.
• "Charisma" factor: Large, charismatic animals (tigers, whales) often attract more public and funding interest for conservation and research than less "appealing" species like slugs or beetles, despite the latter's immense ecological importance.
• Geographic focus: Historically, temperate regions have been better sampled than tropical regions, where biodiversity is much higher.

These factors explain why, even though we have identified millions of animal species, scientists still believe a vast number remain undiscovered, particularly among the smaller and less charismatic invertebrates in biodiverse hotspots.

Which Groups Within Plants and Animals Are the Most Diverse?

When comparing the diversity within the plant and animal kingdoms, certain groups stand out for their sheer number of species. Understanding these highly diverse groups helps illustrate why animals currently hold the lead in terms of known species counts.

Most diverse groups within the Plant Kingdom:

• Flowering Plants (Angiosperms): This is by far the most diverse plant group, accounting for over 90% of all known plant species. Their evolutionary success is due to innovations like flowers (for efficient reproduction) and fruits (for seed dispersal). Examples include roses, oaks, grasses, orchids, and vegetables.
• Ferns and Lycophytes: While significantly less diverse than angiosperms, this group still comprises thousands of species, primarily found in moist, tropical environments.
• Mosses and Liverworts (Bryophytes): These non-vascular plants also contribute a substantial number of species, typically found in damp, shady habitats.

Most diverse groups within the Animal Kingdom:

• Insects (Class Insecta): Unquestionably the most diverse group on Earth, insects account for more than half of all described species. Within insects:
  • Beetles (Order Coleoptera): The most diverse order, with over 350,000 described species.
  • Moths and Butterflies (Order Lepidoptera): Another highly diverse group.
  • Ants, Bees, and Wasps (Order Hymenoptera): Crucial pollinators and social insects with many species.
• Arachnids (Class Arachnida): Spiders, mites, scorpions, and ticks contribute tens of thousands of species. Mites, in particular, are extremely diverse and often overlooked.
• Mollusks (Phylum Mollusca): Snails, slugs, clams, oysters, octopuses – a very diverse group found in marine, freshwater, and terrestrial environments.
• Crustaceans (Subphylum Crustacea): Crabs, lobsters, shrimp, barnacles, and copepods are incredibly diverse, especially in aquatic environments.
• Nematodes (Phylum Nematoda): These tiny roundworms are ubiquitous in almost every environment on Earth. While many are known, scientists suspect millions more remain undiscovered, especially in soil.

The extraordinary diversity of invertebrates, particularly insects, is the primary driver behind the higher number of identified animal species compared to plants.

What is Undescribed Biodiversity, and How Does It Affect Our Understanding?

Undescribed biodiversity refers to the vast number of species that exist on Earth but have not yet been formally discovered, identified, and cataloged by science. This "hidden" diversity significantly affects our understanding of the total number of plant and animal species, suggesting that the current known counts are just the tip of the iceberg.

Impact of undescribed biodiversity:

• Underestimation of Total Species: Scientists widely agree that the total number of species on Earth is much higher than the number currently identified. Estimates for total species range from a conservative 5-10 million to upwards of 30-100 million.
• Greater Unknowns in Certain Groups: The majority of undescribed species are believed to be small, cryptic, or inhabit hard-to-reach environments. This includes:
  • Insects: Especially in tropical rainforests. Many insects are highly specialized and localized.
  • Nematodes: Ubiquitous and often morphologically similar, making identification challenging.
  • Fungi: A vast, largely unexplored kingdom.
  • Marine invertebrates: Deep-sea environments are particularly under-sampled.
  • Microbes: Bacteria, archaea, and viruses represent an immense and largely unquantified biodiversity.
• Implications for Conservation: If we don't know a species exists, we can't protect it. Undescribed biodiversity means that many species may go extinct due to habitat loss and climate change before we even know they were there, leading to a silent erosion of life on Earth.
• Ecological Gaps: A lack of knowledge about species means we have an incomplete picture of ecosystems, food webs, and the critical roles organisms play.

The existence of undescribed biodiversity highlights the ongoing challenge and importance of taxonomic research. It suggests that while animals currently lead in known species, the true disparity might be even greater, or perhaps, the sheer scale of the unknown makes precise comparison difficult.

How Does Habitat Destruction Impact Species Numbers?

Habitat destruction is the leading driver of species loss globally, profoundly impacting the numbers of both plant and animal species. As natural habitats are converted, degraded, or fragmented by human activities, countless species lose their homes and the resources they need to survive, accelerating extinction rates.

Ways habitat destruction impacts species numbers:

• Loss of living space: Direct removal of forests, wetlands, grasslands, and coral reefs eliminates the physical environment where species live, feed, and reproduce.
• Resource depletion: Habitats provide food, water, and shelter. Destruction means these essential resources disappear, making survival impossible.
• Fragmentation: Breaking up large habitats into smaller, isolated patches makes it harder for species to migrate, find mates, or access diverse resources. Small populations in fragments are more vulnerable to genetic bottlenecks and local extinctions.
• Edge effects: The boundaries between natural habitats and human-modified landscapes (edges) often experience different conditions (more light, wind, predators, invasive species) that can negatively impact species adapted to interior habitats.
• Altered ecosystem processes: Habitat destruction can disrupt crucial ecological processes like nutrient cycling, water filtration, and pollination, which affect a wide range of species.
• Increased vulnerability to other threats: Species in degraded habitats are more susceptible to the impacts of climate change, pollution, and invasive species.

Impact on Plant Species: Plants, being sessile, are particularly vulnerable. When their habitat is destroyed, they cannot simply move to a new location. This leads to direct extirpation and loss of unique genetic lineages.

Impact on Animal Species: Animals, while some can move, often depend on specific habitat features for survival. Destruction means loss of food sources, breeding grounds, and cover, leading to population declines and eventual extinction.

The ongoing loss of habitats, particularly in biodiverse regions like rainforests and coral reefs, means that not only are we losing known species, but we are likely losing countless undescribed plant and animal species before we even have a chance to discover them.

Are There Any Major Taxonomic Revisions That Could Change the Numbers Significantly?

Yes, major taxonomic revisions are constantly occurring and can significantly change the official counts of both plant and animal species. Taxonomy, the science of classifying organisms, is a dynamic field, and advances in technology and scientific understanding frequently lead to reevaluations of existing species.

Factors driving taxonomic revisions:

• DNA Sequencing (Molecular Phylogenetics): This is perhaps the most impactful tool. Genetic analysis often reveals that:
  • Cryptic Species: What was once thought to be a single species is actually multiple distinct species that look very similar (e.g., many insects, fungi, some plants). This "splitting" of species tends to increase the total count.
  • Synonymy: What was thought to be several different species are actually variations of the same species. This "lumping" of species tends to decrease the total count, though it's less common for large, well-studied groups.
• New Morphological Data: Closer examination of physical characteristics with advanced microscopy can reveal previously overlooked diagnostic features.
• Ecological and Behavioral Studies: Differences in habitat use, diet, mating calls, or reproductive strategies can indicate distinct species, even if they look similar.
• Geographic Range and Isolation: Populations that have been geographically isolated for long periods often diverge genetically, leading to new species.
• Rediscovery of "Lost" Species: Sometimes species thought to be extinct are rediscovered, adding to the count.

Impact on species numbers:

• Overall Trend: Increase: While some "lumping" occurs, the general trend from modern taxonomic work, especially with molecular data, is the discovery of more cryptic species. This means that revisions tend to increase the estimated total number of species, particularly for highly diverse but morphologically complex groups like insects, fungi, and microbes.
• Refinement of Understanding: These revisions provide a more accurate picture of evolutionary relationships and the true extent of biodiversity.

Therefore, the numbers we cite for identified plant and animal species are not static. They are living figures, continually updated by the dedicated work of taxonomists and molecular biologists around the world, and these revisions almost always point towards an even greater, often hidden, biodiversity.

Why is Knowing the Number of Species Important?

Knowing the number of species, and understanding biodiversity, is critically important for a multitude of reasons, extending far beyond mere academic curiosity. It underpins our understanding of life on Earth, informs conservation efforts, and has profound implications for human well-being.

Key reasons why species counts matter:

• Conservation Prioritization: Knowing how many species exist, where they live, and which are threatened is fundamental to effective conservation. It allows us to identify biodiversity hotspots, prioritize protection efforts, and monitor the health of ecosystems. If we don't know a species exists, we can't protect it.
• Ecosystem Health and Stability: Each species plays a role in its ecosystem, from pollinators and decomposers to predators and prey. A greater diversity of species generally leads to more resilient and productive ecosystems that are better able to withstand disturbances (e.g., disease outbreaks, climate change). Losing species can unravel these complex webs.
• Resource Provision (Ecosystem Services): Biodiversity provides invaluable "ecosystem services" that directly benefit humans:
  • Food: All our food sources (crops, livestock, fish) depend on biodiversity.
  • Medicine: Many vital medicines are derived from plants, animals, or fungi (e.g., penicillin from fungi, aspirin from willow bark). The vast majority of species have not been screened for medicinal properties.
  • Clean Air and Water: Plants filter air, and healthy ecosystems filter water.
  • Pollination: Bees, butterflies, and other animals pollinate crops, essential for food security.
  • Soil Fertility: Microbes, fungi, and invertebrates contribute to healthy soil.
• Scientific Research and Understanding: Each species represents a unique evolutionary experiment. Studying different organisms provides insights into biology, genetics, ecology, and the history of life on Earth, leading to scientific breakthroughs.
• Intrinsic Value and Aesthetics: Many people find intrinsic value and aesthetic pleasure in the natural world's diversity. The loss of species diminishes the richness and beauty of our planet.

Ultimately, the number of plant and animal species is a proxy for the health and vitality of our planet. A decline in these numbers signals environmental degradation and poses a direct threat to human societies.

What is the Overall Trend in Species Discovery vs. Extinction?

The overall trend concerning species discovery versus extinction is a concerning one: while new species are continually being discovered, the rate of species extinction is dramatically accelerating, far outpacing discovery. This imbalance is often referred to as a biodiversity crisis.

Trends in Species Discovery:

• Steady pace: Taxonomists are still describing thousands of new species each year, particularly among insects, fungi, and marine invertebrates. Advances in genetic sequencing continue to reveal "cryptic species" that were previously thought to be one.
• Unexplored areas: Many parts of the world (e.g., deep oceans, tropical rainforest canopies, underground systems) remain largely unexplored, promising many more discoveries.

Trends in Species Extinction:

• Accelerated rates: Current extinction rates are estimated to be 100 to 1,000 times the "background" or natural rate of extinction observed in the fossil record. Some scientists argue it could be even higher.
• Main drivers: The primary causes of this accelerated extinction rate are:
  • Habitat loss and degradation: As discussed, this is the leading factor.
  • Climate change: Altering ecosystems faster than species can adapt.
  • Pollution: Contaminating air, water, and soil.
  • Overexploitation: Unsustainable hunting, fishing, and harvesting.
  • Invasive species: Outcompeting or preying on native species.
• Undiscovered extinctions: Many species, especially small invertebrates, are likely going extinct before we even have a chance to discover and describe them, a phenomenon often called "co-extinction" or "dark extinction."

The imbalance: Despite ongoing efforts in species discovery, the sheer volume of species being lost, largely due to human activity, represents a net decline in global biodiversity. This has profound implications for ecosystem stability, human well-being, and the future of life on Earth.